JAPANESE MINKA XXVII - ROOF FRAMING 4: SASU FRAMING 3

A simple yet stable tripod structure can be created by tying three poles together at their heads and spreading their feet apart in two dimensions, making this structure able to resist forces from all directions. Such structures are employed in the Japanese rice-drying racks (haza 稲架) discussed last week, and are also used in Japan and elsewhere to suspend cooking pots over fires. Perhaps the purest example of the use of this principle in minka roof framing (koya-gumi 小屋組) is in the distinctive thatched-wall minka of the Ainu (アイヌ) people, known as chise (チセ).

The Ainu are an ethnic group culturally, linguistically, and genetically distinct from the Japanese; historically their lands extended from the northern part of Honshū, throughout Hokkaidо̄, and into the Kuril Islands, Sakhalin Island, and the tip of the Kamchatka Peninsula.

Ainu people with chise in the background.

Pre-historical and historical range of the Ainu.

Exterior of a chise and associated outbuildings, showing uniformly thatched roof and walls, giving these dwellings a coat-like appearance.

Entrance of a chise.

On the left, a female outhouse called the menokoru; on the right, a male outhouse, called the asinru.

Interior of a chise.

Interior of a chise.

The roof framing (koya-gumi 小屋組) of chise was erected on the ground, then lifted whole onto the horidate-bashira (堀立て柱), posts sunk directly into the ground. These koya-gumi therefore had to be rigid structures that would not deform. The principal rafters (sasu 叉首) of these structures are called ketsunni (ケツンニ). As can be seen in the diagram below, the tripods at each gable end of the roof were spanned by a ridgepole (kitaiomani キタイオマニ); the structural arrangement is identical to that seen in the haza, with two sasu running inwards to bear on the long wall plates (sobeshini ソべシニ), one on each side, and a single sasu running outwards to land in the centre of the gable wall plate (soetomotsueppu ソエトモツェップ). Corners are formed with corner sasu (sanperappunikani サンペラップ二カニ) that meet the ridgepole slightly inwards of the apex of the tripods, and intermediate long-side sasu called sakarikanii (サカリカニー) are then laid from the ridgepole to the long wall plates.

The roof framing of a chise, with members labelled with their Ainu names: the ridgepole (kitaiomani キタイオマニ), intermediate purlins (sakiriomappu サキリオマップ), principal rafters (sakarikanii サカリカニー), end wall plates (soetomotsueppu ソエトモツェップ), long wall plates (sobeshini ソべシニ), transverse beams (umangi ウマンギ) long side rafters (sakarikanii サカリカニー), corner rafters (sanperappunikani サンペラップ二カニ), and gable framing members (ponrikanii ポンリカニー).

The roof structure of a chise showing the three principal rafters (ketsunni ケツンニ) forming the ‘tripod’, and the long side common rafters (hira-sasu 平叉首, here called chisenkarikani チセンカリカニ).

This triangulated arrangement is not limited to the chise of the Ainu. A variation on the basic tripod structure can be seen in minka in Toyama Prefecture, where the koya-gumi consists of three pyramid structures, each consisting of four poles. The end pyramids consist of two sasu running to the corners of the building (called sumi-sasu 隅叉首, lit. ‘corner sasu’); the other two poles of these pyramids, and the four poles of the middle pyramid, are called diagonal principal rafters (sha-sasu or naname-sasu 斜叉首).

Roof structure of a minka in Toayma prefecture, showing three pyramid arrangement, each pyramid having four poles (poles on the rear side of the roof are truncated for clarity).

Roof structure of a minka in Toyama Prefecture showing the diagonal principal rafters (sha-sasu or naname-sasu 斜叉首).

Another variation can be seen in Ishikawa prefecture, where there are pairs of diagonal principal rafters incorporated into the long sides of the roof that meet the inner poles of the end pyramids at their feet, and the long-side sasu (hira-sasu 平叉首) at their tops, to provide longitudinal bracing (see diagram below).

Minka roof framing from Ishikawa prefecture showing two pairs of diagonal principal rafters (sha-sasu or naname-sasu 斜叉首) between the end pyramids and the long side principal rafters (hira-sasu 平叉首).

Roof framing of a minka in Ishikawa prefecture showing diagonal principal rafters (sha-sasu or naname-sasu 斜叉首) and long-side principal rafters (hira-sasu 平叉首).

In both cases, the roofs are steeply pitched acute triangles, and without such triangulating reinforcement these roofs would be prone to leaning or toppling under the heavy wind and snow loads common in Japan’s northern and coastal regions.

JAPANESE MINKA XXVI - ROOF FRAMING 3: SASU FRAMING 2

In cold areas where the snow load on roofs is great, and in large minka where the principal rafters (sasu 叉首) are especially long, roof posts (tsuka 束) are employed at intermediate positions to support the sasu and prevent them from sagging or bending. These posts, in conjunction with the transverse ties or beams that sit on top of them, form a shape that resembles the Shinto torii (鳥居) gate, and so this reinforced sasu-gumi construction is known as torii-gumi (鳥居組). This is something of a hybrid style of construction, somewhere between true sasu-gumi, where the sasu are unsupported along their length, and true wagoya-gumi, where there are no sasu. The transverse elements also serve to prevent the sasu from thrusting outwards and spreading the walls that they terminate on.

A torii gate.

Torii-gumi construction.

Thanks to the trussed form created by the paired sasu and the transverse member that forms the base or bottom chord of the triangle, sasu-gumi structures are very strong in the transverse direction, but they are extremely prone to racking or tipping over in the longitudinal direction.

Various methods have been devised to compensate for this longitudinal weakness. The idea for sasu is thought to have originated in haza (稲架), the simple pole structures erected in paddy fields to dry harvested rice. Stability in these structures is achieved by adding a third leg to the ‘sasu’ pairs at each end to form tripods which brace the structure against longitudinal forces.

In minka roof framing, the equivalent ‘third leg’ members at the ‘gable’ ends (妻側 tsuma-gawa) or short sides of hipped roofs are called oi-sasu (追叉首, lit. ‘following principal rafter’) or mukau-sasu (向かう叉首, lit. ‘facing principal rafter’), in contrast to the ‘regular’ paired sasu in the long sides of the roof, which are called hira-sasu (平叉首, lit. ‘flat principal rafter’). The oi-sasu is tenoned into the underside of the ridgepole (munagi 棟木) just to the outside of the point where the end pair of hira-sasu cross.

Photograph showing how the oi-sasu (追い叉首) is tenoned up into the munagi (棟木) just to the outside of the paired hira-sasu (平叉首, here called sashiki さしき).

JAPANESE MINKA XXXV - ROOF FRAMING 2: SASU FRAMING

Last week’s post introduced the four main roof framing systems employed in Japanese minka. From today we consider the simplest of these systems, sasu-gumi (sasu-gumi 扠首組 or 叉首組) or ‘principal rafter framing,’ in more detail.

Typical example of sasu-gumi (叉首組) framing, showing four pairs of principal rafters (sasu 叉首) and transverse beams (koya-bari 小屋梁), ‘gable end’ rafters (oi-sasu 追叉首), wall plates (noki-geta 軒桁 and tsuma-bari 妻梁), cross bracing (hagai はがい), ridgepole (munagi 棟木), and common rafters (taruki 棰).

The paired principal rafters (sasu 扠首 or 叉首) after which sasu-gumi takes its name are not butt-jointed where they meet at the apex of the roof, but crossed at their upper ends so that some part of the rafters extend beyond the intersection; in the crotches thus formed sits the ridgepole (munagi 棟木). In the most primitive examples, this junction is secured with nothing more than rope, but in most cases some form of joinery is employed, in the form of either a cross half-lapped (aikaki 相欠き) and wedged (sen-uchi 栓打ち) joint, or a pegged mortise and long tenon (naga-hozo-sashi-hana-sen-uchi 長枘差し鼻栓打ち) joint. 　Whichever joint is employed, the ‘handedness’ of each sasu pair is alternated from bay to bay: first right over left, then left over right, and so on, giving greater strength to the whole roof structure.

Two joinery methods for connnecting the sasu at the apex of the roof: on the left, a cross half-lapped (aikaki 相欠き) and wedged (sen-uchi 栓打ち) joint; on the right, a pegged mortise and long tenon (naga-hozo-sashi-hana-sen-uchi 長枘差し鼻栓打ち) joint. The latter also shows how the ridgepole (munagi 棟木) is lapped into the crotch of the rafters.

The lower ends or ‘tails’ of the rafters are shaped down to a pencil-like point, and set into holes cut into either the transverse beams or the wall plates, then secured with wedges. This is a ‘pinned’ connection, meaning the sasu is theoretically only under axial loads and does not experience any bending, because it is unrestrained and free to rotate around the connection point in two axes, like the ball of the femur in the socket of the pelvis. This kind of joint is said to be more resilient than a fixed, rigid connection under loads from wind and earthquake.

Photograph of the apex of a roof showing the sasu joined with cross half-lapped (aikaki 相欠き) and wedged (sen-uchi 栓打ち) joints, and the ridgepole (munagi) carried in the crotches formed.

Two examples of joining the sasu to the beam structure: on the left, orioki-gumi (折置組) framing with the wall plate (keta 桁) over the transverse beam (koya-bari 小屋梁); on the right, kyо̄ro-gumi framing with the transverse beam over the wall plate, and the sasu ((叉首) secured in its hole with a wedge (kui 杭).

Photograph of a carpenter reassembling a minka roof. This is a kyо̄ro-gumi framed roof, with the sasu set into holes in the longitudinal beams (keta) which sit on the transverse beams (koya-bari), though this example has two tiers of both. On the left can be seen a new, pale wedge (kui) holding the much older and darker sasu in place. Diagonal braces (hagai) are also visible.

After the sasu and ridgepole are erected, purlins (commonly called moya 母屋 but here yanaka 屋中) are fixed horizontally to the sasu at around 60-80cm intervals with rope; in addition to restraining the sasu from tipping over, they form a subframe to tie the common rafters (taruki 棰) to. The rope used is regular straw (wara 藁) rope, but it is said that if the rope is made from straw that has first been exposed to winter snow it will last 40 or 50 years; this is comparable to the life of the reed (kaya 茅) thatch used as the roof covering, meaning that when the roof is rethatched the rope can be conveniently replaced at the same time.

JAPANESE MINKA XXXIV - ROOF FRAMING 1

The previous seven posts or so were spent looking at the many varieties of minka roof beam framing (hari-gumi 梁組). But the hari-gumi is just one element of minka roof framing (koya-gumi 小屋組), and we are now finally ready to move on, and up, to consider the roof structure as a whole. It should come as no surprise that here we find perhaps even more variety than that presented by the beam framing, because the koya-gumi consists of the roof beams previously discussed, plus all of the structural elements within the interior of the roof or ‘roof space’ (koya-ura 小屋裏) that are above, and supported by, the beam framing: roof posts (tsuka 束), ties (nuki 貫), purlins/underpurlins (moya 母屋 or yanaka 屋中), principal rafters (sasu 扠首 or 叉首), common rafters (taruki 垂木 or 棰), etc.

In Japanese architectural terminology, elements on the external surfaces on the roof that are visible from the exterior, such as the roof covering (yane-buki 屋根葺き) or roof ornaments (yane-kazari 屋根飾り), are not considered part of the koya-gumi. The names for these elements customarily contain the characters for roof (yane 屋根), whereas internal structural elements, e.g. the transverse roof beams (koya-bari 小屋梁), are by contrast often associated with the word koya.

Koya-gumi can be broadly classified into four main types: sasu-gumi (扠首組 or 叉首組), lit. ‘principal rafter framing’), wa-goya-gumi (和小屋組, lit. ‘Japanese koya framing’), shin-tsuka-gumi (真束組, lit. ‘true post framing’), and nobori-bari-gumi (登り梁組, lit. ‘climbing beam framing’). The sasu-gumi and wa-goya-gumi (sometimes simply called wa-goya) were introduced in a previous post, but this and subsequent posts will go into far more detail.

The sasu-gumi is a primitive trussed or triangulated structure, formed by a pair of round-section log (maruta 丸太) principal rafters (sasu 扠首 or 叉首), which determine the pitch of the roof, and a koya-bari transverse beam as its lower chord. This framing arrangement is simple and strong, but not typically strong enough to bear roof tiles (kawara 瓦), and so it is closely associated with thatched roofs (kusa-yane 草屋根, lit. ‘grass roof’).

Sasu-gumi (叉首組) framing, showing the wall plates (keta 桁), transverse beam (koya-bari 小屋梁), principal rafters (sasu 叉首 or 扠首), purlins (yanaka 屋中), and rafters (taruki 棰).

In contrast, the wa-goya is highly representative of tiled roofs (kawara-yane 瓦屋根), and can also be seen under timber board or plank roofs (ita-yane 板屋根). In this method, vertical posts of around 1 metre in length, called tsuka (束), are set at intervals along the koya-bari; these posts support the underpurlins (moya 母屋) and the ridgepole (munagi 棟木) that run perpendicularly to the koya-bari, and transfer the live and dead roof loads down to the beams. A modernised form of wa-goya framing is the standard roof framing method even today in Japanese new-built houses.

Wa-goya-gumi (和小屋組) framing, showing the wall plates (keta 桁), transverse beam (koya-bari 小屋梁), crown post (shin-tsuka 真束), penetrating tie (nuki 貫), underpurlins (moya 母屋) and ridgepole (munagi 棟木), and rafters (taruki 棰).

A primitive agricultural shelter showing naturally forked perimeter posts supporting wall plates, central posts called muna-mochi-bashira (棟持柱, lit. ‘ridgepole holding post’), also forked, that run from ground to apex and support the ridge pole, and common rafters spanning from ridgepole to wall plates. This structural arrangement is thought to be the progenitor of the wa-goya-gumi, where the obstructive muna-mochi-bashira are replaced with crown posts (shin-tsuka) bearing on transverse beams (koya-bari).

In shin-tsuka-gumi framing, a longitudinal beam called a naka-oki (中置) is set along the centreline of the koya-gumi, and on this beam are erected crown posts (shin-tsuka) which support the ridgepole (munagi 棟木). Thick rafters span from the ridge to the eaves beams/wall plates (noki-geta 軒桁). This form of roof may be tiled, but is more commonly thatched, and is also common amongst the board/plank-roofed minka of the Shinshū region. Older minka with thatched roofs and shin-tsuka-gumi framing can be found in every region of the country; in these minka the rafters are mainly thick bamboo or timber poles, the central ridge-supporting crown post is called the odachi, among other names, and the method of construction is known as odachi-gumi. In some areas the type is known as burari-zukuri, because of the way the rafters hang or dangle down (burari-agaru ぶら下がる) from the ridge.

Odachi-gumi (おだち組) or shin-tsuka-gumi (真束組) framing, showing transverse beam (koya-bari, unlabelled), longitudinal beam (naka-oki 中置), crown post (odachi おだち), ridge pole (munagi 棟木), and bamboo rafters (kudari-dake くだり竹).

Nobori-bari-gumi framing was commonly employed when the roof space was required for storage or work, as it is a framing method by which this space can be opened up and/or made taller for those purposes. The transverse beams, here called zushi-yuka-bari (厨子床梁, lit. ‘zushi floor beam’; a zushi is a portable Buddhist shrine/altar) are tenoned into the posts at a level somewhat lower than the heads of the posts; these beams support a central longitudinal beam (naka-oki 中置) upon which are set crown posts (shin-tsuka 真束) a large longitudinal beam called a jimune (地棟) is run along the top of the shin-tsuka at the apex of the roof space and just below the ridgepole (munagi); inclined beams (nobori-bari 登り梁) at the same pitch as the roof span from the jimune down to the heads of the wall posts; purlins/underpurlins (moya 母屋) are set directly onto these inclined beams and themselves support the common rafters (taruki 棰).

Nobori-bari-gumi (登り梁組) framing, showing the transverse beam (zushi-yuka-bari 厨子床梁), tenoned (sashitsuke 差付け) into the posts, the central longitudinal beam (naka-oki 中置), crown post (shin-tsuka 真束), the beam brackets or ledges called makura-gi (枕木, lit. ‘pillow timber’, i.e. ‘sleeper’), rising beams (nobori-bari 登り梁), longitudinal apex beam (ji-mune 地棟), purlins or underpurlins (moya 母屋) and common rafters (taruki 棰).

JAPANESE MINKA XXXIII - BEAM FRAMING 7

The previous post briefly mentioned the roof beam framing system known as honya-date (本家建て, lit. ‘true house construction’). In this system, the roof framing (and associated posts) consists of two elements or assemblies: the upper roof or jо̄ya (上屋, lit. ‘upper house’) and the lower roof or geya (下屋, lit. ‘lower house’). The jо̄ya and geya were defined and discussed in a previous entry as part of the series on posts, which can be read here. Today we will a look briefly at some of the variation seen within honya-date framing, as a way of concluding our series on the beam framing of minka. This post, and indeed this series as a whole, only presents representative examples of the main beam framing systems; in reality there is huge variety in these types, both from region to region and within regions.

A typical example of honya-date construction showing the jо̄ya (上屋), which consists of the inner, taller jо̄ya posts (jо̄ya-bashira 上屋柱) and transverse beams (koya-bari 小屋梁) that support the principal rafter framing (sasu-gumi 扠首組); and the geya (下屋), which consists of the outer, shorter perimeter geya posts (geya-bashira 下屋柱) and associated wall plates (keta 桁), which support the common rafters (taruki 棰) and roof covering that extend past the external wall plane to form the eaves. Note the principal rafters (sasu 扠首) have pointed ends which terminate at the junction between the koya-gumi and the longitudinal beam known as the kusa-keta (草桁, lit. ‘grass beam’).

The beam framing system of simpler, hut-like structures, which lack a geya, are called suya-date (素家建て, lit. ‘basic house construction’).

Two examples of soya-date construction: orioki-gumi (折置組) framing on the left, and kyо̄ro-gumi (京呂組) framing on the right.

The relationship between the jо̄ya and geya in the simplest honya-date structure can be seen in the section diagram on the left below (the Furui 古井 house). The outer, shorter geya posts (geya-bashira 下屋柱) and inner, longer jо̄ya posts (jо̄ya-bashira 上屋柱) are connected with thick ties called tsunagi-nuki (繋貫, lit. ‘connecting tie’). However, because the inner row of jо̄ya posts along the long sides of the building present a hindrance in the use of the internal spaces, various methods were devised so as to be able to omit some or all of these posts. Jо̄ya posts that do not ‘get in the way’, because they are in the plane of a partition wall along the line of the ridgepole or in the plane of other partitions, can be linked by inclined/raked beams to the lower geya posts in the plane of the external perimeter walls; roof posts (tsuka 束) erected on these beams support the upper jо̄ya beams above, forming a two-tiered beam structure (the section diagram on the right below). There are many regional variations on this method of construction.

On the left, the Furui house showing geya and jо̄ya posts connected with tsunagi-nuki (繋貫). On the right, an example from the Tо̄hoku region where the jо̄ya posts have been replaced with roof posts (tsuka) that bear on a pair of inclined beams (orioki 折置), which frees up the interior. Orioki framing (ori-oki-gumi 折置組) refers to the framing system where the transverse beams sit directly on the external wall posts, and the wall plates are above and supported on the transverse beams.

An example of orioki-gumi framing where the jо̄ya post is replaced by a short roof post (tsuka 束) that bears on the lower transverse beam (koya-bari 小屋梁) and supports the upper transverse beam and upper longitudinal beam (jо̄ya-geta 上屋桁) of a two-tiered beam system.

Examples of honya-date minka from the Kantо̄ region. On the left, an example of the structural style known as shikata-geya-zukuri (四方下屋造り lit. ‘four direction geya construction’) with six transverse posts. On the left, a style from the same region known as odachi-zukuri (おだち造り) where some of the obstructive internal posts can be omitted by the use of longer, curved transverse beams. The odachi is the crown post that supports the ridgepole and common rafters (taruki 棰); note that there are no principal rafters (sasu 扠首) in this system.

Examples of honya-date minka from the Chūgoku region. In the example on the right, the internal post is offset to the right in order to create a larger unobstructed space on the left; in the example on the left, the internal post is omitted altogether by the use of a large central longitudinal beam (nakabiki-hari 中引梁).

Section of a small minka on Amami О̄shima (whose unique minka are discussed in last week’s post). The construction method shown here is called sasuya-zukuri (さすや造り), where the principal rafters (here called sashiki さしき) bear directly and only on the wall plates (hon-geta 本桁) without any intermediate roof posts, beams or ties. A single tier of transverse beams called kyakuro (きゃくろ), of the same dimension as the posts, serve as both beams and head rails for the sliding partitions. The method is unusual in that there are inner and outer posts, but the common rafters terminate at the same point as the principal rafters, indicating that this is a suya-date (素家建て) rather than honya-date (本家建て) construction, as it lacks a geya.

In the famous gasshо̄-zukuri style of minka seen in Toyama and Gifu Prefectures, the geya is skilfully resolved by having the ends of hockey-stick shaped beams called chо̄na-bari (ちょうな梁, lit. ‘adze beam’, not because the beam is adzed but because its shape is like that of an adze handle) bear directly on the external wall plates and geya posts. In Toyama Prefecture, this method of construction is called maieya-zukuri (まいえや造り). Many of the minka of Shirakawa (白川村), Gifu Prefecture, have chо̄na-bari only on the facade side of the structure; the rear is either two-post honya-date, or suya-date construction. This hybrid style is called katagi-zukuri かたぎ造り.

Example of a gasshо̄-zukuri style minka showing a massive curved beam (chо̄na-bari ちょうな梁) on the right, spanning from the internal post to the external wall post (geya-bashira 下屋柱), allowing the omission of the internal jо̄ya post (jо̄ya-bashira 上屋柱), here called the chakuro-bashira (ちゃくろ柱).

Photograph taken during rethatching of a gasshо̄-zukuri minka, showing the curved transverse beam (chо̄na-bari ちょうな梁) bearing on the longitudinal wall plate (keta 桁) and geya post.

JAPANESE MINKA XXXII - BEAM FRAMING 6

A hikimun-zukuri minka on Amami О̄shima.

On the subtropical Amami archipelago (Amami Guntо̄ 奄美群島) between Kyūshū and Okinawa, in particular on the main island of Amami О̄shima (奄美大島), minka employ a structural system called hikimun-zukuri (ひきむん造り). The minka of these islands are of the sebuntо̄-gata (分棟型, lit. ‘separate ridge form’) shо̄tо̄-bunritsu (小棟分立, lit. ‘small ridge separate standing’) form: small, structurally independent and often physically separate structures, each for a particular function, e.g. cooking, ‘living’, etc.; there are no huge, magnificent roofs as can be seen on the mainland. The simplest form is called sasuya-zukuri (さすや造り). Posts are closely set at around 0.5 or 1 ken centres, and linked at uchi-nori (内法, lit. ‘inner measure’) height by keta-uke-bari (桁受け梁) beams of the same dimension as the posts. The uchi-nori height is the ‘head’ height, i.e. the dimension from the top of the floor sill (the finished floor level) to the underside of the lintel. This dimension was based on the length of a tatami mat, which in turn was taken from the average height of an adult male in the Muromachi and Edo eras, around 154 to 156cm, and was eventually standardized at 5 shaku (尺) 7 sun (寸), or around 173cm. Thus in the oldest and most primitive Amami minka, the uchi-nori is too low to hang a ceiling, and the posts within rooms make the living spaces difficult to use.

In minka on the mainland, the nuisance of internal posts was eliminated as joinery became more sophisticated, and deep, tenoned beams and lintel beams (sashi-gamoi 差鴨居) capable of greater spans appeared; on these beams were erected roof posts (tsuka 束) to support the roof, turning the sasu-gumi (扠首組) structure into a wagoya-gumi (和小屋組) structure.

On the Amami islands, there was an almost identical development in the hikimun-zukuri, which takes its name from the fact that both the beams and lintels there are called hikimun (ひきむん or 引物). The name literally means ‘pull thing’ or ‘draw thing’, presumably because these beams are ‘drawn’ or ‘strung’ between or around the tops of the posts, at uchi-nori height. The hikimun became larger in section to achieve longer spans, and the structure also evolved to increase ‘head space’: the interior posts were increased in height, so becoming jо̄ya-bashira (上屋柱, ‘upper roof post’), and above the hikimun were added another set of beams, called kakure-hikimun (隠れひきむん, lit. ‘hidden pull thing’) because they are hidden above the ceiling now made possible by the increased post height.

There is major point of difference between the evolution of these two systems, however. Whereas on the mainland deepened beams were given correspondingly deep tenons and slotted into sides of the posts, on the Amami islands the hikimun were wider, and square vertical holes were cut into them, with lower beams having larger holes than upper beams. The beams were dropped from above onto the square posts, which are progressively stepped down in section to match the dimensions of the holes in the posts.

Drawings and photographs of the hikimun-zukuri framing system.

Drawing showing how the hikimun (ヒキムン) fit over the stepped jо̄ya-bashira (上屋柱) posts. The posts drop into the floor beams (neda ネダ) in a similar way, but pegged below the beams. The assembly has an almost toy-like appeal in its simplicity.

The transverse members (beams or lintel beams) are set onto the posts first, followed by the longitudinal wall beams/plates. The former have grooves planed into their soffits to receive sliding partitions. Above the ceiling there is another tier of beams (kakure-hikimun). At the highest level, at the top of the internal ring of posts, are wall plates called hon-geta (本桁, lit. ‘true wall beam’ though it should be noted that in honya-date construction they are not actually in the plane of the external walls) that support the principal rafters (sasu 扠首, here called sashiki さしき) and common rafters (taruki 垂木, here called kichi きち) and transverse beams called sasu-uke-bari (扠首受梁, lit. ‘common rafter bearing beam’). On the mainland this system is called honya-date (本家建て, lit. ‘true house construction’) which will be discussed in greater detail in future posts.

Section drawing of the Nakamura House, Amami О̄shima. This hikimun-zukuri structure has a distinct division between jо̄ya and geya, but in this example there is a curved hikimun beam spanning the full distance between perimeter geya posts.

Detail photograph of the Hikimun-zukuri construction of the Nakamura House. The post (hashira 柱) steps down in section as it rises; the wide hikimun (ひきむん) and kakure-hikimun (かくれひきむん) longitudinal and transverse beams are dropped onto the post from above. At the top of the post are the transverse sasu-uke-bari (扠首受梁) beams and the hon-geta (本桁) wall plates supporting the principal rafters (sashiki さしき) and common rafters (kichi きち). Note that in this example the principal rafter doesn’t directly bear on the sasu-uke-bari, but is offset to the left.

In later examples of hikimun-zukuri, the transverse hikimun at uchi-nori height might be omitted. Instead, only a grooved head (kamoi 鴨居) attached to a rail (nageshi 長押) or tie (nuki 貫) was used above the opening, and above that a bulkhead (ari-kabe 蟻壁 or 有壁) consisting of planks or boards.

Section drawing of the Furumi House, Amami О̄shima. An example of hikimun-zukuri construction where there is a transverse hikimun at the upper jо̄ya level but not at the uchi-nori level, where there is only a relatively shallow . The bulkheads (ari-kabe 蟻壁 or 有壁) above the kamoi consist of single wide planks of Japanese cedar (sugi, Cryptomeria japonica)

Photographic detail of the beam framing of the Furumi House.

Diagrammatised drawing of the photograph above. There are longitudinal and transverse hikimun (ひきむん) at uchi-nori height (内法高) and the transverse hikmun at this location is grooved to take sliding partitions; this is in contrast to the section drawing above, where there is only a kamoi and nageshi with no transverse hikimun. Above the transverse hikimun is a timber board (hame-ita 羽目板) bulkhead (ari-kabe 有壁) and above that are the ceiling boards (tenjо̄-ita 天井板). Above the ceiling are the kakutre-hikimun (かくれひきむん) beams, then at the top of the post the longitudinal ‘wall plate’ (hon-keta ほんけた) and transverse common rafter bearing beam (sasu-uke-bari 扠首受梁).

The ‘stepped’ or ‘tapered’ post method of construction is also seen in the floor framing of the raised-floor storehouses called taka-kura (高倉, lit. ‘high storehouse’) of Hachijо̄-jima (八丈島), an island in the Izu chain (Izu Shotо̄ 伊豆諸島) south of Tokyo, where the floor beams are dropped onto the posts from above.

A taka-kura on Hachijо̄-jima.

The same taka-kura as above from a different angle.

These are simple joints that have arisen from primitive tools and techniques. Yet the system may also be seen as a rational one: there are no tenons to twist or snap under lateral loads from the cyclonic winds that the islands are exposed to.

JAPANESE MINKA XXXI - BEAM FRAMING 5

Last week’s post looked at one structural response to the high snow loads of the Hokuriku region of northern Japan: the waku no uchi zukuri method of beam framing. There are also gable-entry, front doma (mae-doma-gata 前土間型), hiroma-gata (ひろま型, ‘living room type’) plan form dwellings whose post layout differs from that of the typical waku no uchi zukuri, and it follows that their beam framing system also differs. In these minka, four main posts are located at the internal boundaries of the iri-gawa 入側 on each side of the dwelling, and form a square or rectangle. The iri-gawa is the corridor-like space at the building perimeter between the inner zashiki and the external verandah (nure-en 濡れ縁), typically of 1 ken width and often with a raked ceiling under a lean-to roof.

A very refined example of an iri-gawa 入側 in a relatively modern traditional building.

A fifth ‘centrepiece’ post, the naka-bashira, is placed more or less in the centre of the dwelling. These posts together are referred to as go-yaku 五役, lit. ‘five roles’).

Diagrammatic example of a five post (go-yaku 五役) gable-entry, front doma (mae-doma-gata 前土間型) minka.

Of the two posts at the boundary between the raised floor rooms and the earth-floored doma (here called niwa にわ), the post on the uwa-te (上手) side (the right side when looking from the niwa towards the raised floor rooms) near the entrance (kado-guchi) is nominated as the daikoku-bashira (大黒柱); that on the shimo-te (下手) side (the left side) near the sink and oven/stove is variously called the ebisu-bashira (えびす柱 or 恵比須柱, Ebisu is a Japanese deity), nagashi-bashira (流し柱, lit. ‘sink post’) or in some areas toudai-bashira (灯台柱, lit. ‘lamp post’), because the location of this post at the heart of the danran (団らん, the ‘family circle’) meant that a shelf was often attached to it for a lamp to sit on to illuminate the space.　

As for the beam framing, the terminology is somewhat confusingly and contradictorily presented in my sources. The main longitudinal beam (ushi-bari 丑梁, lit. ‘ox beam’), here known as the komokake-bari (菰掛梁, lit. ‘mat hanging beam’), spans from the naka-bashira (中柱) post across the front raised floor rooms and the niwa to a post in the facade wall known as the ushi-bashira (丑柱, lit. ‘ox post’) or komokake-bashira (菰掛柱, lit. ‘mat hanging post’); this beam is crossed at right angles by a beam called the norikoshi-hari (乗越梁, lit. ‘ride over beam’) or komo-tsuri (菰吊り, lit. ‘mat hanger’) which spans between the daikoku and ebisu posts. On the interior sides of the iri-gawa, spanning from the daikoku-bashira and ebisu-bashira posts back to the two other main posts (unnamed) in line with the naka-bashira, and parallel with the ushi-bari, are two longitudinal beams called the keta-uke-bari (桁受梁). This is a basic layout but as always there are many variations.

In these minka, the round ‘log’ beams such as the ushi-bari are referred to as marumon (まるもん, lit. ‘round thing’), and the lintel beams (sashi-gamoi 差鴨居) are called hiramon (ひらもん, lit. ‘flat thing’). On the beams are set roof posts (tsuka-bashira 束柱) supporting the ‘upper roof’ beams (jо̄ya-bari 上屋梁) which in turn support the tsushi-yuka (つし床) floor. This type of two-tiered beam framing is known as maya-date (真家建て, lit. ‘true house construction’). The principal rafters (sasu 扠首) terminate at the upper roof beams above the keta-uke-bari, i.e. on the internal sides of the iri-gawa; only the common rafters (taruki 垂木 or 棰) extend out to the longitudinal external walls and the lower roof (geya 下屋) structure. These rafters are called kudari-take くだり竹, lit. ‘descending bamboo’; as they are visible from within the interior, they may be covered with a reed screen (yoshi-zu 葦簀) lining.

A photograph of the interior a ‘five post’ (go-yaku) minka, looking towards the naka-bashira post in the raised floor zashiki.

The central longitudinal beam (ushi-bari) runs from the naka-bashira post on the left off to the ushi-bashira (丑柱) post outside the frame on the right. Bearing on the ushi-bari is the transverse beam here labelled komo-kake-bari (菰掛梁), in contradiction to the diagrammatic plan above, where it is labelled norikoshi-hari (乗越梁) and komo-kake-bari is given as an alternative name for the ushi-bari. In any case, sitting on the beam can be seen a rolled-up komo (Zizania latifolia) mat, from which the beam takes its name.

Dimly in the background can be seen the keta-uke-bari (桁受梁) beam running parallel to the ushi-bari.

The plastered infill wall in the plane of the naka-bashira is the bulkhead between two rooms, supported on a lintel beam (sashi-gamoi) with sliding partitions below (both unseen); also in the plane of the bulkhead can be seen two roof posts (tsuka-bashira) bearing on the lintel beam and supporting an upper transverse beam. This beam, together with the beams above the ushi-bari and keta-uke-bari, form a second, upper tier of beams that support the floor of an attic storey with a bamboo floor. Just visible at the right of the image, behind the ushi-bari, is a ladder leading up to this storey.

JAPANESE MINKA XXX - BEAM FRAMING 4

In areas of high snowfall, the beam framing of minka is generally both stouter and more complex than in other areas. In the snowy Tо̄hoku region, even in sasu-gumi framing, roof posts (tsuka 束) are erected under the ridgepole (mune 棟) and internally in order to support the weight of the snow, effectively turning the sasu-gumi into a wa-goya construction where the beams also bear the roof load, transferred to them from the rafters via the tsuka.

Because the amount of snow on a roof is influenced by prevailing wind direction and incident sunlight, and therefore differs between different faces of the same roof, framing methods known as hon-goya (本小屋, lit. ‘true koya’) and masu-zukuri (桝造り, a masu is a square wooden sake cup) were developed, where beams are built up in multiple layers to prevent the twisting of the structure under this uneven load distribution. Examples of these types of construction can be seen above the main ‘gathering’ or ‘social’ rooms and doma in minka across the northern part of the Kantо̄ region and the Tо̄hoku region.

An example of hon-goya framing, with many tiers of beams and ties.

In the Kaga, Nо̄tо̄, and Etchū areas of the Hokuriku region, there is a characteristic form of construction called waku no uchi zukuri (枠の内造り, lit. ‘inside the frame construction’) in which the beam framing above the gathering room (known as the hiroma or oe) forms a strong cross-framed (igeta-gumi 井桁組) structure, and the framing of the other rooms is constructed as an accompaniment around this core. Two daikoku-bashira are erected on the central axis of the room, on opposing sides of the space; these are complemented by four corner posts, giving a total of six posts supporting the jо̄-ya part of the roof structure. Naturally there are many variations on this basic form.

An example of waku no uchi zukuri framing.

A waku no uchi zukuri (枠の内造り) structure showing a massive longitudinal beam (ushimon うしもん or 丑物) bearing on a daikoku-bashira post that looks slender in comparison, and cross beams (harimamon 梁間物).

The waku no uchi zukuri (枠の内造り) structure with various members labelled: the deep lintel beams (hiramon ひらもん, here ヒラモン), roof posts (tsuka 束, here ツカ), and two tiers of penetrating ties (nuki 貫, here ヌキ). Crossing the space are two longitudinal beams (ushimon うしもん) and two transverse beams, with a ‘hollow’ centre, indicating this as an igeta-gumi (井桁組) construction.

This atypical example shows four equal ushimon longitudinal beams, two bearing on main posts and two on roof posts that are in turn supported on the hiramon lintel beam, and a single harimamon cross-beam.

An eight-mat ‘living’ or ‘gathering’ room (hiroma or oe)

The frame of the structure above the level of the openings is formed of three or four tiers of timbers around the perimeter of the space, with infill plastering. The lowest tier, above the openings, consists of massive lintel beams (sashi-gamoi 差鴨居) known as hiramon (ひらもん), grooved to take the sliding partitions. Above this are tiers of ties that penetrate the posts, a longitudinal beam (here known as an ushimon, うしもん or 丑物) that spans across the centre of the space and ties the two daikoku-bashira, and perpendicular to this the cross-beams harimamon (梁間物). This arrangement results in a cruciform structure, but there are also igeta examples with twin ushimon Magnificent large section Japanese zelkova (keyaki 欅) beams finished into an octagonal section. To this strong central framework is added kake-gi (懸木, literal ‘hanging timbers’ for eaves (hisashi 庇) or lean-to structures front and back, and the roof framing of the rooms to the left and right.

JAPANESE MINKA XXIX - BEAM FRAMING 3

Continuing with our examination of longitudinal beams (ji-mune 地棟) in Japanese roof framing (koya-gumi 小屋梁), recall from last week’s post that these beams are called nakabiki-bari (中引梁) when they run above the raised floor zashiki part of the dwelling, and ushi-bari (丑梁) when they run above the earthen-floored doma part of the dwelling. As can be seen in the diagram below, both nakabiki-bari and ushi-bari bear on the large-section daikoku-bashira internal post, at the boundary between zashiki and doma.

At its other end, the ushi-bari may be supported on an large-section ushi-mochi-bashira (丑持 lit. ‘ushi-bearing post’), not shown in the diagram, in the plane of the gable-end external wall. However, because such an oversized post doesn’t ‘fit in’ with the other posts in the gable-end wall, many minka opt for another solution, which is to erect two posts of normal size, with a beam known as a tenbin-bari (天秤梁, lit. ‘balance/scale beam’) between them, and support the ushi-bari on this beam.

A longitudinal beam (ji-mune) supported on a short, deep balance beam (tenbin-bari) tenoned into two posts in the plane of the gable wall.

Photograph showing a) balance beam (tenbin-bari), b) longitudinal beam (ji-mune), and c) ridge pole (muna-gi).

In the Minо̄ and Tо̄hoku regions, there is a beam framing method known as torii-gumi (鳥居組, lit. torii framing), in which posts directly below longitudinal beams are omitted, and all longitudinal beams are supported on tenbin-bari. From the Kansai region west, there are many examples of large minka where ushi-bari are not especially large; instead, a number of beams of uniform size are placed at around 1 ken (1.8 metre) centres and supported on a long tenbin-bari.

Multiple bent ushi-bari bearing on a long beam at right.

As the spans get larger, the beam framing becomes progressively more complex; it is the skilful exploitation of bent or arched beams, and the free, improvised, or ‘emergent’ assembly and interlacing of them into strong structural forms, that is so characteristic of minka beam framing.

On the left, a simple longitudinal beam (ji-mune 地棟) framing system, with a single central ji-mune (either a nakabiki-bari 中引梁 or an ushi-bari 丑梁) supporting a single layer of continuous-span transverse beams (koya-bari 小屋梁). On the right, a more complex system where in addition to the koya-bari there is a lower layer of transverse beams called shiki-bari (敷梁, lit. ‘spreader beam’) or uke-bari (受梁 lit. ‘receiving beam’), tenoned into the posts, that support intermediate longitudinal beams (either ushi-bari or tobihari 飛梁).

A framing system with two layers of transverse beams, as in the previous example, and two layers of longitudinal beams: the ue-ushi or uwa-ushi (上丑, lit. ‘upper ox (beam)’) and shita-ushi (下丑, lit. ‘lower ox (beam)’). The lowest transverse ‘beams’ are sashi-kamoi (差鴨居), head rails with grooved soffits to receive sliding room partitions.

A framing system with a tenbin-bari (天秤梁) supported on twin posts, and supporting the central longitudinal beam (here labelled as an ushi-bari (丑梁), indicating that it runs over the earth-floored doma part of the minka. Riding on the ushi-bari are inclined beams called nagekake-bari (投掛梁, lit. ‘throw beam’) or agari-ki (上り木, lit. ‘rising timber’). Lower tenoned beams called tsunagi-bari or tsuna-bari (繋梁, lit. ‘tie beam’) tie the inner and perimeter posts together.

Photograph showing a balance beam (tenbin-bari) supported on two posts, and supporting a (ji-mune) and two inclined beams (nagekake-bari or agari-ki). This example differs from the one shown in the section diagram above in that the tenbin-bari sits on the heads of the posts rather than being tenoned into their sides, and the nagekake-bari do not bear on the ji-mune and terminate short of it rather than being joined above it; they are supported only on the tenbin-bari.

In the minka of the mountainous areas of Hirano and surrounding districts in the Kantо̄ region, the custom was to use especially bent and twisted beams, perhaps partly because local conditions made it difficult to get hold of large, good quality pine logs, partly out of the carpenters’ desire to show off their skills, and partly as an alternative to, or a kind of, ornamentation: there were many regions where hanging a ceiling was forbidden under sumptuary laws, meaning that the roof structure was unavoidably exposed, so carpenters were no doubt motivated to elevate the beam framing into an aesthetic element by making it as beautiful and interesting as possible.

In the Kantо̄ region, carpenters undertook a preliminary stage known as chi-gumi or ji-kumi (地組, lit. ‘ground framing’), in which the framing was temporarily laid out and assembled on the ground, and the correct heights of roof posts and other members calculated in advance. This was not customary in the Kansai region, however, where carpenters took pride in being able to successfully erect and assemble the beam framing without a ‘dry run’, having first accurately calculated the heights of bent or arched beams using only roku-zumi (陸墨, lit. ‘land ink’, i.e. horizontal reference lines snapped onto the timbers with an inked string).

In sasu-gumi or ‘principal rafter construction’ where there are no posts (tsuka 束) or penetrating ties (nuki 貫), the completion of the beam framing marked the end of the carpenter’s involvement; from there, the villagers, including both experienced roofers (yane-ya 屋根屋) and general hands, would undertake the framing of the principal rafters (sasu 扠首), underpurlins (moya 母屋 or yanaka 屋中) and common rafters (taruki 垂木 or 棰) themselves. This was not complex joinery work but involved mostly rope tying, in which the roofer was more skilled than the carpenter.

JAPANESE MINKA XXVIII - BEAM FRAMING 2

As a rule, transverse (perpendicular to the ridge pole) roof beams (koya-bari 小屋梁) in minka are spaced at two to three metre centres. Transverse beams are always present in minka as they are necessary to prevent the spreading of the longitudinal walls under the thrust action of the rafters, but there may also be beams that run longitudinally (parallel to the ridge pole) where it makes structural or economic sense to do so, such as near the gable ends of the building, where the span from an internal post on the structure’s longitudinal centreline to the gable wall may be shorter than that of the transverse span from the post to the longitudinal walls, but not long enough to justify adding another transverse beam. Framing systems which incorporate longitudinal beams are called ‘cross framing’ (jūji-gumi 十字組 or igeta-gumi 井桁組). Both terms derive from the visual resemblance of the crossed beams to the respective kanji in their names: ‘十’ (ten) and ‘井’ (water well).　

In the simplest structures, a single transverse beam spans the full distance between the longitudinal walls, but in all but the smallest houses the more common practice was to use a central longitudinal beam ji-mune (地棟, ‘ground ridgepole’), supported by an intermediate post or posts, and support the transverse beams (either one continuous-span beam as long as the width of the structure but supported in the middle by the longitudinal beam, or two single-span beams each half the width of the structure, spanning from the longitudinal beam out to their respective wall plates (keta 桁). When it runs over the raised floor zashiki part of the minka, this longitudinal beam is called the nakabiki-bari (中引梁, ‘central pull beam’), and when over the earthen-floored doma it is known as the ushi-bari (丑梁, ‘ox beam’). 　　

The simplest form of roof framing, sasu-gumi (扠首組) or ‘principal rafter framing’, consisting of paired principal rafters and single-span transverse beams between opposing external walls, and no longitudinal beams. The example on the left is orioki-gumi (折置組) framing with the wall plates above the beams, on the right is kyо̄ro-gumi (京呂組) framing with the wall plates below the beams.

A simple example of a cross-framing (jūji-gumi 十字組 or igeta-gumi 井桁組) system, with a central intermediate post bearing a longitudinal beam (nakabiki-bari 中引梁, here an ushi-bari 丑梁). The transverse beams (koya-bari 小屋梁) are carried on top of the longitudinal beam and wall plates (keta 桁), making this an example of kyо̄ro-gumi (京呂組) framing.

An example of ‘cross framing’ (jūji-gumi 十字組 or igeta-gumi 井桁組). Shown are: the daikoku post (daikoku-bashira 大黒柱); the transverse beams (the full-width koya-bari 小屋梁 and the half-width nagekake-bari 投掛梁, lit. ‘throw beam’); the wall plates or wall beams (keta generally, here named noki-geta 軒桁 ‘eave plate’ in the longitudinal wall plane and the tsuma-bari 妻梁, ‘gable plate’ in the gable wall plane); the longitudinal beams (ji-mune 地棟), namely the ushi-bari 丑梁 over the doma and the nakabiki-bari 中引梁over the zashiki; and the and tobi-hari (lit. ‘flying beam’) secondary beams.

There are several ways of resolving the structural relationship between the transverse beam, wall plate, and post:

In the orioki-gumi (折置組, ‘folded framing’) method, the mortised beam and wall plate sit directly on a long, stepped or ‘stacked’ tenon (kasane-hozo 重ね枘) cut into the head of the post, with the wall plate sitting on the beam and cross-lapped (ai-kaki 相欠き) into it.

In the kyо̄ro-gumi (京呂組, lit. ‘capitol backbone framing’) method, the wall plate is mortised into the beam and the beam sits on and is lapped and dovetailed (ari-tsugi 蟻継ぎ; ari 蟻means ‘ant’ and the joint is named for the supposed resemblance of the dovetail tenon to the pinched waist and abdomen of an ant) into the wall plate. There are two variations of the kyо̄ro-gumi: the kabuto-ari (兜蟻, ‘helmeted dovetail’) in which the end of the beam is flush with the outer face of the wall plate, and the watari-ago (渡り腮, lit. ‘crossing jaw’) in which the end of the beam extends out past the wall plate.

In the sashi-zuke (差付け, lit. ‘insert attach’) method, the beam is tenoned and pegged into a through-mortise in the post, and the wall plate sits on the head of the post.

The various methods of forming the junction between post, wall plate, and transverse beam. From top to bottom: orioki-gumi (折置組), kyо̄ro-gumi-kabuto-ari (京呂組兜蟻), kyо̄ro-gumi-watari-ago (京呂組渡り腮) . and sashi-zuke (差付け).

A more detailed comparison of orioki-gumi 折置組 (top) and kyо̄ro-gumi 京呂組 (bottom) methods.

Diagram of the basic joints in Japanese joinery. First column, first row is the ari (蟻) or dovetail joint; first column, third row is the ai-kaki (相欠き) or cross-lapped joint.

A partly dismantled orioki-gumi framed minka showing the exposed stacked or stepped tenon (kasane-hozo 重ねホゾ) at the top of the post.

These various methods each have their own advantages and disadvantages. In the orioki and sashi-zuke methods, there must be a post directly under each beam, whereas in the kyо̄ro method, beams can be placed at any location along the wall plate as long as it is deep enough to bear them, and intermediate posts can be offset from beams or omitted altogether. Orioki and sashi-zuke provide an uninterrupted upper surface of wall plate to support common rafters (taruki 垂木 or 棰), and a ready-formed lip between the beam and the top of the wall plate to set principal rafters (sasu 扠首) into. Orioki and sashi-zuke are older methods, while kyо̄ro is relatively newer.

Example of orioki framing with the transverse beam set directly on top of the head of the post, and a relatively slender wall plate set on top of the beam. A large longitudinal beam can be seen in the foreground, bearing the main transverse beam and a smaller ‘throw beam’.

JAPANESE MINKA XXVII - BEAM FRAMING

After examining the foundations of the minka, then the floor framing, then the wall and post framing, we are now ready to move onwards and upwards to consider easily the most complex, arguably the most interesting, and easily the most beautiful part of the minka structure: the roof structure, or koya-gumi (小屋組). Literally translated, koya means ‘hut’ or ‘small house’ and kumi 組 means ‘set’ or ‘assembly’ and the name is apt: because most minka roofs are pitched very steeply, they are usually the most dominant presence in any minka, both structurally from within (assuming there is no ceiling) and visually from without, making up a far larger proportion of the elevational area of the building than the almost unnoticed walls sheltered beneath their deep eaves. In a way, the roof of the minka is the house.

The thatched roof dominates the exterior elevation of this relatively modest minka.

The minka roof structure consists of various sub-elements: the roof covering, the principal rafters (sasu 扠首) and/or common rafters (taruki 垂木 or 棰), the underpurlins (moya 母屋 or yanaka 屋中), the penetrating ties (nuki 貫), the various short posts (tsuka 束) that transfer loads from the underpurlins to the roof beams (koya-bari 小屋梁), and the roof beams themselves. We begin this subject by looking at the beam framing (hari-gumi 梁組), a huge topic in its own right.

The main role of the beam framing is to resist horizontal forces (from wind and earthquakes) by tying together the heads of the perimeter and internal posts, and so preventing any twisting, warping or leaning of these elements.

In simpler, smaller-span roofs, the beams do not receive vertical roof loads directly; they act purely as tie beams to prevent these opposing walls from spreading apart under the thrusting action of the principal rafters (sasu 扠首). The transverse tie beams and the sasu together form a strong triangulated or ‘trussed’ structure. This type of roof is known as the sasu-gumi (扠首組).

In larger roofs, or where the dead or live roof loads are large, the beams also receive point loads directly from crown posts and other short posts that stand on them, and transfer these loads to the posts below. This type of framing is known as wa-goya (和小屋, lit. ‘Japanese roof’).

Sectional diagrams illustrating the differences between sasu-gumi (top) and wagoya-gumi (bottom) roof framing. In the former, the principal rafters (sasu 扠首) bear on the beams as closely as possible to their ends at the wall posts and wall beams (keta 桁). The sasu carry the underpurlins (yanaka 屋中), which in turn carry the common rafters (taruki 垂木 or 棰). In the latter, the beams support various posts (tsuka 束) at intermediate points; on these posts are carried the underpurlins (moya 母屋) and ridgepole (munagi 棟木) which carry the common rafters.

Japanese carpenters of the past were of what might be called the ‘paperweight school’: the thinking was that by making the roof structure as heavy as possible, and thereby pushing the whole house down from above, a more robust structure could be achieved. Remember that minka were not fixed to their foundations, as today’s houses are with steel anchor bolts and such; rather the posts simply sat on their foundation stones, with nothing to stop the building from lifting or shifting in a typhoon or earthquake, other than its own weight. The general custom was to make beams larger than necessary, and to stack them up in double or triple layers, even where the expected stresses were not particularly great from the point of view of preventing twisting and racking in the walls, especially where there were few, small openings in the perimeter.

Beams were typically pine (matsu 松), left more or less as ‘trunks’ in the round, either only with the bark removed (oni-gawa-mugi 鬼皮剝ぎ, lit. ‘ogre skin peeling’), or worked with an adze to form roughly flat surfaces between rounded corners (tsuma-kawa-mugi 爪皮剝ぎ) . The tsuma-kawa 爪皮 is the toe covering of geta, the traditional wooden sandals of Japan. More elaborately, the sides of the beam might be worked back to achieve a consistent width (taiko-otoshi 太鼓落とし, lit. ‘drum reduction’), or the beam might be shaped into an octagonal profile (hachi-men-dori 八面取り, lit. ‘eight side taking’).

When using bent or twisted timbers as beams, these timbers would be oriented to take advantage of the bend to form an arch, with the ‘rise’ (mukuri 起り) or ‘back’ of the beam oriented upwards, which is both structurally stronger and visually ‘correct’.

A magnificent example of wa-goya roof framing, showing beams running in both directions, arched beams, stacked beams, supporting posts, penetrating ties, principal rafters, underpurlins, and rafters.

VERNACULAR PICTURES 17: CORRUGATED LANESCAPES

The central and iconic role played by corrugated iron (of course, what is commonly referred to as ‘corrugated iron’ or even ‘tin’ has for a long time been corrugated steel, and has never been tin) in the vernacular building of Australia is well recognised; I have even seen Australia referred to as ‘the spiritual home of corrugated iron’. But what comes to most people’s minds when they think of this material is rural farm buildings isolated in paddocks, or the painted and galvanised iron roofs of inner-urban terraces and worker’s cottages, or the modern elevation of corrugated iron into an ‘architectural’ material by Glenn Murcutt et. al. Less well recognised is the use of corrugated iron in the sheds and fences lining the back alleys and laneways of older Australian cities and towns.

Back lanes present an entirely different picture to the well-manicured gardens and orderly weatherboard and brick houses that front the long, narrow blocks of old Australian neighbourhoods. The ‘lanescape’ is a jumble of weathered colours and textures, jungle-like growths of trees, plants and weeds, gravel and cobble paving, bits of machinery, dumped appliances, and building detritus. Often the iron used has been taken from the roof of the main house when it was no longer fit for that purpose, so there are mismatched sheets, flaking paint, lap-lines, rust holes, etc. Graffiti and stickers are common modern additions.

These lanes in a sense represent the purest kind of vernacular architecture, since they are completely unselfconscious, completely artless, and their ‘design effects’ are completely unintentional.

Sadly, due to the immense development pressure exerted on traditional residential neighbourhoods by Australia’s insanely high rate of migration and attendant population growth, backyards are being relentlessly infilled with bland unit developments, with their back fences and sheds replaced by treeless, charmless straight lines of colorbond. As the facades and streetscapes of old neighbourhoods are often heritage-protected, these serene frontages are truly a ‘facade’ in the sense that they conceal the destruction and loss of the ‘inner’ character going on behind.

Rear of a modern unit development with ubiquitous ‘fence profile’ colorbond fence.

JAPANESE MINKA XXVI - DAIKOKU POSTS 2

As the largest and most important ‘principal posts’ (yaku-bashira 役柱) in a minka, daikoku-bashira (大黒柱) will naturally be located fairly centrally within the structure, which could hardly be otherwise when you consider that the reason they are regarded as ‘principal’ in the first place is because they gather roof loads over a wide area. There may be more than one ‘principal post’ in a single dwelling, and whether or not these posts are considered to be daikoku-bashira, or some dialect variation thereof (as we will see there is a bewildering variety of alternative names), or some other type of ‘principal post’ entirely, seems to be a somewhat arbitrary or nominal matter, or at least to a large degree a matter of regional convention. Nor is there any specific structural role or configuration that one can point to as definitive of a daikoku-bashira, or as distinguishing or not distinguishing a daikoku-bashira from another type of yaku-bashira, other than that the size and structural importance of both set them apart from the ‘regular’ posts in the dwelling.

In a regular four-room (seigata-yon-madori 制型４間取り) layout, with the partitions between the raised-floor rooms arranged in a cross, there will usually be a daikoku-bashira at the intersection between the two rooms adjacent to the earth-floored doma and the doma itself; there may also be one at the centre of the cross where the four raised-floor rooms meet, and one in the doma. These principal posts are usually mortised to receive tenoned beams or lintels on all four of their sides; the roof loads are transferred via these beams into the posts. Because the beams usually all enter the post at the same height, the cross-sectional area of the post at this height is greatly reduced. To compensate, the post must be ‘super-sized’ well above that of a regular post so that even after mortising it is still strong enough to carry the loads expected of it. These posts are typically 20 to 30cm square, but posts of 50cm or more are not uncommon. Furthermore, whereas small-section posts are usually of conifer species such as Japanese cedar (sugi 杉, Cryptomeria japonica), Japanese cypress (hinoki 桧, Chamacyparis obtusa), or various species of pine (matsu 松 Pinus sp.), daikoku-bashira are usually made from stronger hardwoods such as Japanese chestnut (kuri 栗, Castanea crenata), Japanese zelkova (keyaki 欅, Zelkova serrata) or oak (kashi 樫, Quercus sp.), although in older houses large pine posts left in their natural trunk-like forms can also be found.

When placed in a line of smaller, normal-sized posts, such large posts will of course be much wider than the sills and headers tenoned into them. On the tatami-floored zashiki (the raised-floor ‘living’ area of the minka) side of the post, the corners of the oversized post will intrude into the corners of the tatami mats abutting it. One early solution to this was to make the tatami mats in a special shape, with a corner notched out to accommodate the post. This solution seems to have been disfavoured, giving rise to the inverse practice of instead taking a notch out of the post itself at the level of the tatami, and slotting a normally-shaped tatami into it. Alternatively, where the daikoku-bashira bordered the doma, a later solution was to shift the post off-axis towards the doma, so that the face of the post on the zashiki side was aligned with the sill and rail, though this could mean that the post might be loaded somewhat eccentrically. In any case, the method by which this problem was solved is one of the clues available to the architectural historian in trying to determine the age of a minka, or at least in establishing the general era in which it was built.

The daikoku-bashira is much wider than the sills and beams tenoned into it. In this case, the solution adopted is to shift the daikoku-bashira off its axes towards the doma, so that the faces of the post on the zashiki side are aligned with the inner edges of the sills, allowing the tatami mats to remain regular rectangles in shape. This method suggests that the minka is of relatively recent construction.

The plans below illustrate some of the different positions daikoku-bashira can take within different types of minka.

Three examples of the different positions daikoku-bashira can take in different minka types. The first plan is a regular four-room layout (seigata-yon-madori 制型４間取り) with three principal posts: one at the intersection of the four raised-floor rooms, one at the edge or the raised floor and the earthen-floored doma (どま), and one in the doma at the corner of the stable (umaya 厩). The second is a ‘divided ridge’ (buntо̄-gata 分棟型) layout, with a single daikoku-bashira towards the rear of the earth-floored ‘cookhouse’ (kamaya 釜屋) near the oven/stove (kamado 釜土), indicated as two circles inside a rectangle. The dashed parallel vertical lines indicate the box gutter between the two roofs. The third is a ‘Yamato ridge construction’ (yamato-mune-zukuri 大和棟造り) layout.

As mentioned, daikoku-bashira are most often, but not always, located at the boundary of the doma and the raised-floor ‘living’ rooms (‘A’ in the first and third plans above). There are many dialect variants for the name daikoku-bashira, including daigoku-bashira (大極柱 lit. ‘great-most post’), tatezome-bashira (建初柱 lit. stand-first post, ichiban-bashira (一番柱 lit. ‘number one post’), ichino-daikoku (一の大黒 lit. ‘number one daikoku’, and teishu-bashira (亭主柱 lit. head/master/husband post’. In the Chūgoku region, the daikoku-bashira enshrines the oven/stove (kamado 釜土) deity (kami 神) Dokujin (土公人), so it is called the rokkū bashira (ロックウ柱).

The ‘B’ posts that stand in the centre of the raised-floor section of the minka are variously called uwa-daikoku or ue-daikoku (上大黒 lit. ‘upper daikoku’), yokoza-daikoku (横座大黒 lit. ‘side sit daikoku’), ushiro-daikoku (後大黒 lit. ‘behind daikoku’), chо̄ja-bashira (長者柱 lit. ‘rich man post’), miyako-bashira (都柱 lit. ‘capital post’), ko-daikoku (小大黒 lit. ‘small daikoku’) ebisu-bashira (エビス柱 lit. ‘Ebisu post’; Ebisu is another of the Seven Gods of Fortune), naka-bashira (中柱 lit. ‘middle post’), etc.

The posts marked ‘C’ in the plans stand in the doma and ‘look across’ at the ‘A’ posts. They are often called niwa-daikoku (庭大黒 lit. ‘garden daikoku’; niwa is an alternate name for doma), shita-daikoku (下大黒 lit. ‘lower daikoku’, or umaya-daikoku (廐大黒 lit. ‘stable daikoku’; other regional variations are mukau-daikoku (向かう大黒 lit. ‘facing daikoku’), nirami-daikoku (睨み大黒 lit. ‘glaring daikoku’), ko-daikoku (小大黒 lit. ‘small daikoku), ebisu-bashira (蛭子柱 lit. ‘Ebisu post’), ushimochi-bashira (牛持ち柱 lit. ‘cow holding post’), etc. When the doma is deep front-to-back, there may be a second principal post in it, in the vicinity of the ‘fireplace’ (kajiba 火事場) near the back doorway (sekoguchi 背戸口); this post is variously called the mizu-daikoku (水大黒 lit. ‘water daikoku), kama-bashira (釜柱 lit. ‘oven/stove post’, or kо̄jin-bashira (荒神柱 lit. ‘storm god post’).　

A daikoku-bashira (here called a niwa-daikoku 庭大黒) standing in the middle of the doma (here called the niwa 庭). The beams tenoned into it support at least two mezzanine levels.

View of the cooking area of a doma. In the foreground is the niwa-daikoku, towards the rear is the mizu-daikoku or kama-daikoku. These posts support a mezzanine floor (chū-ni-kai 中二階) between them for storage.

In the ‘divided-ridge’ type (buntо̄-gata 分棟型) minka (where the living and cooking functions of the dwelling are separated into two structurally distinct entities, each with its own roof ridge) of the Tokai (東海) region, there is no daikoku-bashira in the living structure or ‘main house’ (omoya 主屋) part of the minka; that title is reserved for the principal post in the rear part of the ‘cookhouse’ or ‘stove house’ (kamaya 釜屋). In the minka of Yamato Kawauchi (大和河内), the ‘C’ post, called hanakami-bashira (はなかみ柱) is larger and more esteemed than the ‘A’ post. Some say hanakami-bashira is an alternate pronunciation of kamakami-bashira (釜神柱), but the name is more commonly thought to be a holdover from a time when living and cooking quarters were separated, as in the the aforementioned example of the buntо̄-gata minka, where the daikoku-bashira is in the cooking structure, and the post was in the rearward or ‘upper’ (kami 上) part of the ‘edge’ or ‘peripheral’ (hana 端) house, that is to say the cookhouse; therefore hanakami-bashira can be written 端上柱.

Image of a ‘divided-ridge’ type (buntо̄-gata 分棟型) minka showing the ‘passage’ area of the doma where the main house to the left and cookhouse to the right meet; above is a box gutter linking the eaves of the two roofs, supported by a short stump on a beam tenoned into the daikoku-bashira standing next to the oven/stove (kama or kamado 釜 or 釜) in the ‘cookhouse’ (kamaya 釜屋). Here the daikoku-bashira is called an ue-bashira or uwa-bashira (上柱). Note that there is no principal post in the main house. This layout corresponds to the third plan in the examples depicted above.

JAPANESE MINKA XXV - DAIKOKU POSTS

In the Japanese pantheon, Daikoku-ten (大黒天), or simply Daikoku (大黒), is the god of wealth and guardian of farmers, and one of the ‘Seven Gods of Luck’ (shichi-fuku-jin 七福神). He is associated with the continental deity Mahākāla (who is both the Tantric Buddhist protector of the Dharma and the manifestation of the Hindu god Shiva), and also with the native Shintо̄ kami Ōkuninushi (大国主). Daikoku also gives his name to the daikoku-bashira (大黒柱) or ‘daikoku post’, a term which originally denoted a pillar or pole that enshrined the deity, but at some point took on the more purely architectural definition it has today: the most important and largest post in a traditional Japanese house.

A massive daikoku-bashira at the boundary of the doma and the raised floor, with deep beams tenoned into it on all four sides.

In minka, the daikoku-bashira is usually located at the boundary or point of intersection between the earth-floored doma and the front and rear raised-floor rooms adjacent to the doma; these are all ‘social spaces’ and thus relatively large, so the daikoku-bashira must bear the load from a large area of the roof, transferred to it via the various roof beams spanning these spaces. The daikoku-bashira is thus considered to be the heart of the house, structurally, symbolically and even spiritually, as an atavistic reminder of the timber poles used in ancient Japanese religious ceremonies, of a time when the ‘material subject’ was pre-eminent and central in Japanese architecture and was served by the space around it, before the later evolution of a pure ‘architecture of space’ (a progression traced by Inoue Mitsue in his book Space in Japanese Architecture, perhaps a good topic for a future post).

A man squatting next to a daikoku-bashira, giving a sense of its dimensions. Various beams with their long, deep tenons are also shown.

As discussed in a previous entry, in early minka posts were spaced about one ken (approx. 1.8m) apart and roof loads were evenly distributed over these posts. ‘Special’ posts of unusually large dimensions were rarely required, and even where they appear, they were not normally given any special status or name. Later, when modes of occupying the minka became more sophisticated and there arose the need for conveniences such as being able to comfortably pass between two rooms or use them as a single space, these closely-pitched posts came to been seen as a nuisance, and the desire to remove them motivated important advances in joinery (sashimono 指物), notably the invention of the long, deep lintel beam (sashigamoi 差鴨居), tenoned at either end into posts and with grooves or tracks cut into its soffit (underside) to receive sliding partitions, whether of the paper-covered lattice (shо̄ji 障子) or opaque variety (fusuma 襖). The sashigamoi combines the functions of the shallow, grooved ‘header’ or ‘head jamb’ known as the kamoi (鴨居) and the beam (梁) into one member; put differently, the kamoi was greatly deepened, transforming it into a beam capable of carrying the load of the roof structure. In this way, clear spans (and thus clear openings) of two ken (3.6m) or more were achievable. Incidentally, some degree of deflection or ‘creep’ (sag) in the sashigamoi did not cause the sliding partitions to bind in their tracks, as the grooves in the sashigamoi are cut much deeper than those in the corresponding tracked sill (shikii 敷居) in the floor. This extra head space is necessary to be able to remove the partitions, which is done by lifting the partition up into the ‘pocket’ so that its lower edge clears the tracks in the shikii and can be swung outwards; the partition can then be freed by lowering it out of the sashigamoi.

A deep sashigamoi spanning two ken between rooms, tenoned into a daikoku-bashira on the left. The tracks cut into the sashigamoi to receive sliding partitions (removed) are visible in its soffit.

JAPANESE MINKA XXIV - UDATSU POSTS

An udatsu post (udatsu bashira うだつ柱) is a ‘through-post’ that runs from the ground (or ground sill) all the way up to the apex of the roof, thus transferring the load of the roof directly from the ridge pole to the ground. The word udatsu, or alternatively udachi, is an ancient one. Generally it is written with the character 梲; in manyо̄gana (万葉仮名, the ancient writing system developed from around the 5th century AD to represent native Japanese words phonetically by using Chinese characters) it is written 宇太知. Whether udatsu/udachi is an ancient Japanese word that pre-dated Chinese contact and was only later assigned kanji, or a word of Chinese origin that accompanied the arrival of continental architecture into Japan, is unclear. The etymology points to the word originally referring to a short post (tsuka-bashira 束柱) that stands on a roof beam and runs to the ridge pole (in English known as a king post if in tension or a crown post if in compression) or under-purlin (a queen post).

An ancient haniwa (terracotta figures made from the 3rd - 6th century AD) of a building, with a stout udatsu supporting the ridge.

Many minka, whether with thatched or plank/board clad roofs, used a construction method known as ‘rafter construction’ (taruki kо̄zо̄ 棰構造), where only posts supporting the ridge are used; stout rafters (taruki, 棰 or 垂木) span from the ridge to the wall beams/plates, without intermediate support from under-purlins on queen posts. As a result, in most cases tsuka-bashira/udatsu referred to a ridge-supporting post, and eventually udatsu came to refer to such posts exclusively.

In Japan the grandest udatsu bashira are found in the gable-roofed (kiri-zuma zukuri 切妻造り) minka of the Kо̄shū (甲 州) region, old Kai Province, now Yamanashi Prefecture.

Diagram of a gabled roof. The hafu (破風) part of the gable wall (tsuma 妻) is highlighted in blue.

Often the voluminous roof spaces of these minka are used for sericulture and are divided up into two or three levels. The locals call the tall, large-section posts that run uninterrupted from their foundation stones to the ridge, penetrating each level along the way, udatsu. These posts are used both in the plane of the gable wall and at internal locations; the former are visible from the exterior, and because of their location at the gable end, are called happо̄-udatsu, happо̄ being a common alternate name for hafu.

An interior view of the third storey of a three-storey minka, showing two interior udatsu-bashira running up from the floor below and supporting the ridge pole above.

A gable-roofed building in Yamanashi Prefecture with a slender happо̄-udatsu post running from the ground to the ridge, bisecting the central openings on the upper floors. The beams are tenoned and wedged into the post.

JAPANESE MINKA XXIII - FORKED POSTS

Posts made with forked trunks that divide naturally into two branches at their upper end are called in Japanese mata-ki bashira (股木柱) lit. ‘crotch-tree-post’. Sitting a ridge pole or wall beam/plate in the ‘crotch’ and lashing it to the post is among the simplest and most reliable methods of joining these two members, and requires little to no technical skill to construct, so the technique is often seen in utility structures such as storehouses and charcoal huts where more refined methods are either not required or not achievable. No doubt mata-ki were also prized by the builders of the pit-dwellings of prehistoric Japan, but no physical remains of these timber and thatch dwellings have survived.

Mata-gi bashira supporting the ridge pole on a primitive open-walled structure.

When mata-ki bashira are found in minka, their incorporation into the structure is often more sophisticated, giving the impression that the builders relished the design challenges and aesthetic possibilities these irregular timbers presented. In the doma of the Takano House in Shioyama, Yamagata Prefecture, designated an important cultural property, there is a 60cm diameter chestnut post whose upper end is left in its natural, forked state. The posts passes right through the second storey to bear the floor beams of the the upper second storey; not only the crotch of the post but also the legs support these beams, with the beam supported by the legs running perpendicular to the beam in the crotch. These upper floors, used to dry hay and medicinal herbs, storage, and sericulture, are examples of ‘zara-ban-yuka’, lit. ‘rough board floor’, i.e. thin slat-like floorboards laid with generous gaps between them to facilitate ventilation.

The massive mata-gi bashira in the Takano House

In the Hirakawa house in Maruoka, Fukuoka Prefecture, the mata-ki bashira are used at the four corners of the jou-ya and ge-ya, with each post carrying loads in two directions, from both jōya and geya wall beams. Even if the ‘legs’ of the post are cut off level at the ‘crotch’, the ‘flare’ of the timber remains, and provides a wider bearing surface to accommodate multiple horizontal members.

Mata-gi bashira in the Hirakawa House.

This method avoids the need for complicated joints at the corners, and is sturdy and structurally satisfactory, with the caveat that because a moment (torque) is induced in the eccentrically loaded post there is a tendency over time for the foot of the post to twist. This is an issue where posts are tenoned into ground sills, i.e. rotationally constrained, but was not a concern in minka which employed the horidate-bashira method of setting posts directly into the ground (a method which was still common even in the early 19th century in more isolated rural areas), as the base of the post is free to rotate in its hole.

Another mata-gi bashira in the Hirakawa House. The front ‘leg’ seems to have been cut off at the crotch and supports a large transverse beam. The rear leg remains and supports a smaller beam at a higher level. Note also the large natural concavity on the left-hand side of the post

Mata-gi-bashira are often seen in the minka of the Hokuriku region and vicinity, where they attracted some colourful local names befitting their unusual appearance. More generally they were called dōshiyō-bashira, which might be translated as ‘either way post’. In old Etchū province, modern day Toyama Prefecture, they were called ‘rabbit posts’ usagi-bashira, due to the resemblance of the forked end to a rabbit’s ears; in the northern part of old Hida Province, now northern Gifu Prefecture, they were called ‘peek posts’, by association with the act of ‘crotch peeking’ i.e. bending over at the waist and looking backwards and upside-down through one’s own legs.

JAPANESE MINKA XXII - POST MODULES

One point of difference between modern houses and traditional minka is that in most old minka there is no standard size for posts. Even within a single minka every post is unique in its dimensions, even if only slightly, because each was hand-worked and finished from hand-selected timbers, and posts of appropriate dimensions were selected for every location, depending on the size of the load, the span between partitions, and other considerations. This is in contrast to today’s machine-milled posts, which are all essentially ‘fungible’ and of uniform dimensions, typically 90 x 90 or 120 x 120mm.

Nor was the customary post pitch (spacing) of one ken (間) standard throughout time and place. The modern ken is defined as 1,818mm. In older minka, pitches greater than this were relatively common. In regional terms, the difference can be broadly classified into the jōhō-ryū (上方流) or ‘jōhō style’ (Jōhō is an old name for the western region of Honshū centred around the old capital, Kyōto) which employed a larger ken, and the kantō-ryu (関東流), the ‘Kanto style’ (Kantō being the eastern region of Honshū centred around Tōkyō, formerly Edo), which used a smaller ken.

This regional difference persists in modern construction. Today there are three main module systems still in use in Japan: the kyō-ma 京間 or ‘Kyoto ken’ of 1,910mm plus post width, the chū-kyō-ma 中京間 or ‘reduced Kyoto ken’ of 1,820mm plus post width, and the edo-ma 江戸間 ‘Edo ken’ a.k.a inaka-ma 田舎間 ‘country ken’ of 1,820mm. That the chū-kyō-ma and edo-ma seem at first glance to be identical is explained by the fact that the kyō-ma and chū-kyō-ma are ‘double module’ systems, called in Japanese ūchi-hō-sei (内法制, lit. ‘inner system’) or tatami-wari (畳割り, lit. ‘tatami division’), where the first module is measured from inner post face to inner post face, and the second module is the dimension of the post, while the edo-ma is a ‘single module’ system, called in Japanese shin-shin-sei (心々制, lit. ‘heart-heart system’) or hashira-wari (柱割り, lit. ‘post division’), where the ken is measured from post centre to post centre.

As the name tatami-wari suggests, the use of a double module arises from prioritising the uniformity of tatami mat sizes over that of post spacing, and allows for a standardised tatami mat of 1,910mm x 955mm under the kyō-ma system, or 1,820mm x 910mm in the chū-kyō-ma system. In contrast, in a centre-to-centre single module system such as the edo-ma, tatami mats are sized to fit around the fixed post module. Remember that in minka the floor covering does not go from skirting board to skirting board between walls, or flow uninterrupted from room to room at openings, as it does in a western house with floorboards or carpet; there is either a visible ‘tatami stop’ (tatami-yose, 畳寄せ) at the base of the half-timbered walls, or a sill (shikii 敷居) at openings, marking the threshold between rooms, with shallow tracks cut into it to receive the sliding room partitions. Both tatami-yose and shikii are generally of the same width as the posts, i.e. their vertical faces are flush with the faces of the posts, and their upper horizontal surfaces are at finished floor level, i.e. flush with the surface of the tatami.

A renovated minka showing the tracks cut into the floor beams or bearers (ōbiki) and sills (shikii) to take the sliding room partitions, now mostly removed.

Image showing the shikii threshold between two tatami rooms and the tatami-yose at the base of the half-timbered walls.

As an example, consider a room of one ken square. In the edo-ma system, the post spacing in each direction is 1,820mm centre-to-centre. Assuming a post dimension, and therefore a sill width, of 90mm, this means that in a two-mat room, i.e. a room that is 1 ken square, the tatami mat length must be 1,820 - 90 = 1,730mm to fit between the posts, and the width 1,730/2 = 865mm. If 120mm posts are used, this centre-to-centre dimension remains unchanged at 1,820mm, but the tatami mats will now need to be 1,820 - 120 = 1,700mm in length and 1,700/2 = 750mm in width.

A 1 x 1 ken, two-mat room with 90 x 90mm posts on the edo-ma or inaka-ma module.

In a room that is 2 ken square, the corner post spacing in the edo-ma system is simply 1,820 x 2 = 3,640mm centre-to-centre. In this case, the tatami mat length must be (3,640 - 90)/2 = 1,775mm, and the width 887.5mm.

A 2 x 2 ken, eight-mat room with 90 x 90mm posts on the edo-ma or inaka-ma module.

Using the double module chū-kyō-ma system, the tatami mat dimensions are fixed at 1,820 x 910mm regardless of the size of the room, and the posts and sills are fit around them. So in a 1 x 1 ken, two-mat room, the actual post centre-to-centre dimension is the length of the mat (1,820mm) plus half the post dimension at either side, i.e. 1,820 + (2 x 45) = 1,910mm. If 120mm posts are used, the centre-to-centre dimension will become 1,820 + (2 x 60) = 1,940mm.

A 1 x 1 ken, two-mat room with 90 x 90mm posts on the chū-kyō-ma module.

In a 2 ken square, eight-mat room built on the chū-kyō-ma module, with 90mm posts, the corner post spacing is (2 x 1,820) = 3,640mm between internal post faces and (2 x 1,820) + 90 = 3,730mm centre-to-centre.

A 2 x 2 ken, eight-mat room with 90 x 90mm posts on the chū-kyō-ma module.

There have been other regional variations on the length of the primary construction module that have not survived into modern times, among them the 1,760mm + post width double module kaga-ma (加賀間) of the old Kaga province, modern-day Ishikawa Prefecture, in the Hokuriku region of north-central Japan. In general, the regions where tatami mats earliest appeared (from the Kinki region westwards) used the tatami-wari system; in regions where sericulture was practised and other areas where board floors remained common (from the Chūbu region eastwards), the hashira-wari system often predominated. There are also instances of the two different systems being used within the same minka: the double module system in the raised-floor living area of the dwelling, and the single-module in the earthen-floored doma utility area. In the famous silkworm-rearing village of Shirakawa in old Hida Province (now northern Gifu Prefecture), many of the minka have posts in their tatami-floored spaces with a centre-to-centre pitch of 1,850mm, while the board-floored and doma areas of the dwellings show pitches of 1,970mm and 2,120mm.

JAPANESE MINKA XXI - POST ARRANGEMENT

This week we extend our examination of posts (hashira 柱) in minka to consider them within the context of the whole building, in both structural and planning aspects. This will require going into the subject of the roof structure (koya 小屋) of minka, which means getting ahead of ourselves somewhat, as roofs will be treated separately in more detail in future entries.

In old minka, it was the rule that posts were always placed directly under each end of every koya-bari ( 小屋梁), the main transverse roof beams that carry the load of the roof structure.

The type of roof structure (koya 小屋) shown here, known as Wa-goya, ‘Japanese roof framing’, is still in common use. Three transverse roof beams (koya-bari 小屋梁) can be seen. Note that there is no post under the end of the middle koya-bari, indicating this to be a modern example of the Wa-goya. Diagonal bracing, in both vertical and horizontal planes, is also something not typically seen in traditional minka roof framing.

In addition to these posts, most minka, other than the smallest and simplest, also made use of internal posts providing intermediate support to the roof beams. These are typically placed at a spacing of around one ken (間) or six Japanese feet (shaku 尺, 303mm), standardised in modern times at 1,818mm. These internal posts are usually positioned at the locations of internal partitions, but free-standing posts can also be seen, in the earthen-floored doma and niwa utility areas of many minka. In old minka, the regularity of the post spacing was often strictly maintained, and this emphasis on structure could often be at the expense of practicality and function, resulting in posts that were ‘stranded’ outside of partition lines and in the middle of spaces. While these posts are often ‘in the way’ in practical terms, their existence indicates that they were either considered advisable from a structural standpoint, or unavoidable from an economic one, if roof beams capable of spanning greater distances were not available or affordable.

The roofs of many minka display a two-part structure, with an ‘upper roof’ (jо̄-ya 上屋) and ‘lower roof’ (ge-ya 下屋). The jо̄-ya is the main, inner structure, consisting of the sasu-gumi (叉首組) framing: the principal purlins (moya 母屋) and principal rafters (sasu 叉首) that support them. These members are carried on tall internal posts called jо̄-ya bashira (上屋柱). The ge-ya bashira (下屋柱) are the shorter posts that ring the perimeter of the building in the plane of the external wall, and carry the load of the common rafters (taruki 垂木) and the thick layer of thatch, but not the sasu, which terminate at the ends of the koya-bari at the top of the jо̄-ya bashira.

In many minka, the ge-ya bashira are relatively slender and placed at a pitch of half a ken to one ken, while the stouter jо̄-ya bashira are spaced at one ken.

The two rings of jо̄-ya and ge-ya posts are typically around half a ken or 909mm apart, forming a kind of perimeter colonnade which presents various design possibilities that were exploited in later periods, by using the space to form raised verandahs (engawa 縁側), built-in closets (oshi-ire 押入), alcoves, etc.

If the eaves are particularly deep, the ends of the rafters might be supported with a further ring of free-standing external posts, as seen on the left-hand side of the section below.

Post layout plan of the Furui residence showing the inner ring of jо̄-ya posts at one ken spacing, the outer ring of ge-ya posts at both half ken and one ken spacing, posts at internal partitions, and one free-standing post in the centre of the niwa (にわ).

Photograph of the Furui residence showing the free-standing post in the middle of the niwa.

Transverse section through a minka showing the inner taller jо̄-ya posts supporting the sasu-gumi (note the sasu with pointed ends terminating at the junction between the koya-gumi and jо̄-ya bashira) and the outer shorter ge-ya posts at the external walls supporting only the rafters and roof covering.

JAPANESE MINKA XX - POSTS

Defined functionally, a post is a slender, vertical structural member that, in a single storey building under normal conditions, transfers loads from the roof down into the ground via the foundation. The difference between a post and a column is not strictly defined, but ‘post’ is typically used to refer to relatively small-section timber, and sometimes steel, members, and ‘column’ to stone, steel, concrete, and large-section timber members, particularly in a classical context. In Japanese, all of the above are conveniently called hashira (柱).

Timber columns (with entasis) at Hōryū-ji, Nara Prefecture, 8th century.

Timber posts in a modern Japanese post-and-beam house under construction. The vertical members are temporary bracing.

A massive 240mm square hinoki (Japanese cypress) post (or column?) in a new traditional-style house.

Previous entries in this series have considered posts in minka only in relation to foundations, and in particular to the three different ways the load transfer from post to ground is achieved: setting the posts straight into the ground (hori-date 堀立て), setting them on foundation stones (ishiba-date 石場建て), or using a groundsill (土台敷き). This and the next few entries will focus on posts in their own right.

In modern Japan, posts are almost always made from either Japanese cedar (sugi, 杉, Cryptomeria japonica) or Japanese cypress (hinoki, 桧/檜, Chamaecyparis obtusa). Both species produce timber that is straight-grained, strong, and relatively soft and easy to work. In the feudal period, sumptuary laws in many parts of this country restricted the use of these timbers to the upper classes, so commoners made use of a much larger variety of species, including conifers like black pine (kuro-matsu, 黒松, Pinus thunbergii), red pine (aka-matsu, 赤松, Pinus densiflora), and hemlock (tsuga, 栂, Tsuga sieboldii), and hardwoods like the lacquer tree (urushi, 漆, Toxicodendron vernicifluum) and zelkova (keyaki, 欅, Zelkova serrata).

In the centuries before finer woodworking tools had been developed, and even in much later times in isolated mountain villages where these tools were not available, posts in minka were only minimally worked with an adze to give them reasonably flat faces. Because of the difficulty of working some species, and the poor structural characteristics of others, posts were typically far larger in section than is seen today. Sometimes bent and even forked timbers were used, giving these posts the appearance of standing trees; naturally the principle was to keep the orientation the same, i.e. with the crown end up and the root end down.

Walls in post-and-beam structures, including minka, consist of a ‘skeleton’ of loadbearing vertical and horizontal linear elements, with the spaces between them infilled or covered with largely non-structural material such as wattle and daub and timber cladding; this is opposed to ‘planar’ structures such as loadbearing masonry (and arguably also timber stud-wall), where the structural element is the whole monolithic wall itself. The Japanese term jiku-gumi (軸組), literally ‘axial assembly’ but perhaps best translated as ‘wall framing,’ refers to the assembly consisting of all the individual structural elements contained within the vertical plane of the wall: posts, tied together at their bases with ground sills, and at their heads with wall or perimeter beams, and along their length with horizontal penetrating ties (nuki, 貫) at roughly one metre centres, wedged into through-mortises in the posts. Where there are openings, this basic structural assembly is augmented by the use of lintels and sills.

A traditional Japanese ‘half-timbered’ wall under construction, showing posts, ground sills or ground beams, wall beams, three intermediate penetrating ties, and an infill of split bamboo wattle, before the application of the daub.

Close-up view of penetrating ties (nuki) wedged into through-mortises in the posts.

An obvious difference between traditional Japanese and European post-and-beam framing is that Japanese buildings did not employ the principle of the truss or quasi-truss; that is to say, they contained no ‘triangulating’ diagonal members (sujikai, 筋違) in the wall plane to brace the structure against lateral loads from wind and earthquake; instead, these forces were taken up entirely by the closely-fitted timber joints and tightly wedged penetrating ties.

A European half-timbered building, showing diagonal bracing and ‘quasi-truss’ elements.

A Japanese half-timbered temple building with no diagonal bracing elements.

There are obviously limits to what such a structural system can withstand, but up to a point it was very effective in absorbing the energy of lateral loads via the mechanism of local deformation (crushing) of the timber at the joints and tie penetrations; the surviving structure could then simply be re-plumbed and re-trued and the wedges driven further in to remove the deformation-induced play. The effectiveness of this system is heavily dependent on the high level of precision and accuracy in the joinery, which is only made possible by the use of fine saws and chisels; similar resistance to lateral loads could not be expected of earlier or more primitive minka with their crude adze-cut joints.

JAPANESE MINKA XIX - FLOOR STRUCTURE 2: RAISED FLOORS 3

Any region blessed with a high-quality building material in abundance, be that timber, stone, clay, etc., will naturally develop extraction, processing, and other value-adding commercial industries around this resource, for ‘export’ to surrounding regions and further afield. In isolated mountain villages and on remote islands, however, there may be no economical or practical way to get the resource or its products out to the wider world. This ‘landlocked’ condition, combined with the resource’s abundance, may mean that it has little or no commercial value, and so it will only be used locally, and in ways that might be considered wasteful in other circumstances, because there is no economic motivation to maximise yield and therefore profit. This has historically been the case in some regions of Japan in regards to timber, and has resulted in a floor framing method known as dai-neda-zukuri or о̄-neda-zukuri (大根太造り), ‘large joist construction’. In this method, the time-consuming work of rip-sawing and finishing many standard-dimension bearers (大引 о̄biki), joists (neda, 根太), and stumps (yuka-tsuka, 床束) is foregone in favour of fewer, larger-section joists, notched into similarly oversized, beam-like bearers which require fewer or no stumps to span between walls. Thick floorboards or planks are then fixed to these bearers and joists.

Floor framing showing large-section, beam-like bearers with few or no stumps supporting them, notched out to receive thick joists, which have been removed in this image.

An interesting comparison to о̄-neda-zukuri construction can be made with another variation in floor framing, this time a modern one only developed in recent years, known as neda-resu (根太レス) or neda-non (根太ノン) construction. Here, joists are entirely absent, replaced by 24, 28, or even 32mm thick structural plywood sheets fixed directly to a ‘lattice’ of bearers at 910mm centres in both directions.

On the left: standard modern Japanese floor framing consisting of bearers-joists-floorboards. On the right, a recent innovation, ‘joistless’ construction: thick structural plywood sheets laid directly on bi-directional bearers.

These two floor framing systems represent solutions to what are essentially inverted material and technological conditions, and could further be taken as representative of a characteristic difference between pre-industrial and industrial worlds. Whereas the conditions that gave rise to о̄-neda-zukuri method were the abundance of a resource (high quality, large-section timber) and the lack of technology required to fully exploit it (specifically the lack of technology required to extract and transport the timber economically), in the case of neda-resu construction, it is the scarcity of the resource, and the presence of the relatively sophisticated technology (peeling lathes, defect scanners, modern adhesives, hot presses, etc.) required to produce the structural plywood that makes the system both possible and economical.