JAPANESE MINKA XXXI - ROOF FRAMING 9: WAGOYA FRAMING

The defining feature of wa-goya-gumi (和小屋組, lit. ‘Japanese roof framing’) construction, in contrast to the other forms of roof framing (koya-gumi 小屋組) we have considered to this point, are the rows of roof posts (koya-tsuka 小屋束) erected on top of the transverse roof beams (koya-bari 小屋梁). These roof posts transfer the dead load of the roof indirectly to the ground floor posts (hashira 柱) via the beams. In most wa-goya roof framing, the rows of roof posts support underpurlins (moya 母屋) which support the common rafters (taruki 棰 or 垂木); wa-goya roofs do not typically have principal rafters (sasu 叉首), but as we shall see there are examples which do.

Wa-goya roof framing is still commonly used in new-build houses in Japan today, in a somewhat rationalised form, with metal hardware and diagonal bracing to improve performance under lateral load from wind and earthquake, and squared, straight roof beams.

Modern wa-goya-gumi (和小屋組) roof framing, showing posts (hashira 柱), wall beams (noki-geta 軒桁), transverse roof beams (koya-bari 小屋梁), corner bracing (hi-uchi-bari 火打梁), roof posts( koya-tsuka 小屋束), penetrating ties (koya-nuki 小屋貫), diagonal bracing (koya-sujikai 小屋筋交), underpurlins (moya 母屋), ridge beam (munagi 棟木), and rafters (taruki 垂木). Only one half of the roof is shown for clarity.

In most traditional minka, the roof beams are irregular, curved pine logs (matsu-maruta 松丸太); in order to minimise deflection, these beams are oriented so that their ‘backs’ face upwards, forming a natural arch, meaning that the roof posts in any particular longitudinal row of posts are not of uniform length. The posts are connected and restrained from leaning out of plumb in both longitudinal and transverse directions by penetrating roof ties (koya-nuki 小屋貫); the upper and lower faces of these ties are typically in contact with one another within the roof posts (i.e. their mortises are connected); however in older minka the transverse and longitudinal ties may be widely vertically separated.

If the width of the building is large and cannot be spanned by a single transverse beam, it is divided into two or three spans by intermediate posts, usually located in the plane of the floor plan partitions where they won’t be in the way of the inhabitants. Longitudinal (parallel to the ridge) beams, called shiki-bari (敷梁) or nakabiki-bari (中引梁), support two transverse beams called nage-kake-bari (投掛梁) that run out to the external walls on either side. The longitudinal beams might be supported directly on the internal posts, or in the middle of a short, elevated transverse beam called a tenbin-bari (天秤梁).

Wide-span buildings can give rise to another problem: the roof posts may be too long to be effectively stabilised, even with penetrating ties. In this case, one solution is to add one or two tiers of roof beams above the main roof beams, arranging them so that roof loads are distributed as evenly as possible.

The following five section diagrams illustrate how wa-goya framing developed to accommodate greater spans by the use of tiered beams, longitudinal beams, and internal ground floor posts:

1. A simple short-span wa-goya roof with only three rows of roof posts (koya-tsuka 小屋束) on the transverse beams (koya-bari 小屋梁), and underpurlins and a ridgepole set on the roof posts to carry the common rafters (taruki 棰).

2. A wider building, but still spannable by a single koya-bari, and five rows of koya-tsuka; the central three rows of longer koya-tsuka are stabilised by penetrating ties (koya-nuki 小屋貫) in both directions.

3. The wide span is divided into two with a row of internal ground floor posts (hashira 柱), upon which is set a longitudinal beam (naka-biki-bari 中引梁); the naka-biki-bari supports two transverse beams called nage-kake-bari (投掛梁). There are eight rows of koya-tsuka, an upper transverse beam (ni-ju-bari 二重梁), and above that shorter connecting beams (tsunagi-bari つなぎ梁) which stabilise the structure in place of penetrating ties (nuki 貫).

4. The building is divided into three spans, with two rows of internal ground floor posts. The two outer transverse beams (tsunagi-bari 繋梁) act to tie the posts together but do not bear any of the roof load. The central, elevated ‘balance beam’ (tenbin-bari 天秤梁) carries a massive central longitudinal beam, which in turn supports two transverse ‘rising beams’ (nobori-bari 登り梁); it is these nobori-bari which bear the roof load via nine rows of koya-tsuka.

5. Again there are three spans, but this building employs a very long transverse beam that runs the full width of the building and forms three continuous spans over the two internal ground floor posts; on this beam is carried a longitudinal beam (naka-biki-bari 中引梁), which in turn carries two nage-kake-bari (投掛梁) transverse beams. There are two additional tiers of transverse beams above this: the ni-ju-bari (二重梁) and san-ju-bari (三重梁). There are eleven rows of koya-tsuka, although note that some terminate at the san-ju-bari and some at the ni-ju-bari, without directly transferring their roof loads down to the nage-kake-bari.

Wa-goya roof framing is typically associated with tiled roofs, but thatched examples can also be found in areas with heavy snowfall and on particularly large roofs.

If the sasu-gumi (叉首組) framing method covered in the last few posts is employed in large-span minka, there arises the need to support the long principal rafters (sasu 叉首) at intermediate points to prevent them sagging. This need led to the development of sasu-gumi into the more complex torii-gumi (鳥居組) method, also discussed previously, in which two roof posts flanking the central odachi post support underpurlins (moya 母屋) that in turn support the sasu. This system might be regarded either as a precursor form of wa-goya construction, or perhaps a hybrid of the two systems. Such combination roofs are commonly found from the Chūbu (中部) region northwards, in the Tо̄hoku (東北) region, and elsewhere.

A wa-goya roof that incorporates principal rafters (sasu) in Akita Prefecture in northern Japan, an area of high snowfall.

The Sasaki house in Nagano Prefecture, a region of high snowfall. The roof framing incorporates wa-goya-gumi elements (roof posts, upper roof beams, penetrating ties) into a sasu-gumi roof structure.

Section diagram of the Sasaki house. The curves in the long continuous transverse roof beam (koya-bari 小屋梁) are cleverly oriented to ‘snake’ around the two outer longitudinal beams (uke-bari 受梁), which support it, and the central longitudinal beam (ji-mune 地棟), which it supports. Three rows of roof posts (koya-tsuka 小屋束) bear on these beams and are connected with penetrating ties (koya-nuki 小屋貫) in both directions. The uppermost central roof post is termed the shin-tsuka (真束). Interestingly, the roof run is divided into two rows of half-length sasu: the upper (sasu 叉首) and lower (kiri-sasu 切り叉首, lit. ‘cut sasu’).

A similar structure to the Sasaki house, but without an upper central crown post (shin-tsuka) The principal rafters (sasu 叉首) and upper transverse beams (tsunagi-bari 繋梁) form an A-frame structure in the upper half of the roof space; in the lower half, three rows of roof posts (koya-tsuka 小屋束) transfer loads to the roof beams below.

A roof in Tochigi Prefecture showing central roof post (shin-tsuka 真束) and two flanking roof posts (waki-tsuka 脇束) to support the principal rafters (sasu 叉首).

A partly disassembled minka in Kanagawa Prefecture with roof framing that utilises both crown posts (odachi おだち) and principal rafters (sasu 叉首). Note that the sasu are not full-length from ridge to eaves; rather the run is divided into upper sasu (simply called sasu) and shorter, more slender lower sasu (kiri-sasu 切り叉首).

The magnificent thatched wa-goya roof of the Egawa House in Shizuoka Prefecture. A forest of roof posts, thicker and longer than the ground floor posts in the average minka, are connected with equally numerous penetrating ties, the whole forming a dense three-dimensional lattice.

JAPANESE MINKA XXX - ROOF FRAMING 8: ODACHI FRAMING 2

Many examples of odachi-gumi (おだち組) construction can or could be found in the Tanba (丹波) and Hokusetsu (丹波) regions of western Honshū, corresponding to parts of the modern Prefectures of Kyо̄to (京都), Hyо̄go (兵庫) and О̄saka (大阪).　　

Photo of odachi-gumi roof framing in the Tanba region, Kyо̄to Prefecture. Labelled are the crown post (odachi おだち) supporting the ridgepole (munagi 棟木), and thick common rafters (taruki たるき) running from ridge to eaves. There are no principal rafters (sasu 叉首).

The tail ends of the common rafters visible are at the eaves of this odachi-gumi roof (the same as in the photo above).

In the Hirai (平井) farmhouse in Kо̄be City (神戸市), a row of odachi (which at 180mm square are much larger than the ground floor posts below) are set along a 300mm square longitudinal roof beam (naka-oki 中置).

A row of stout odachi in the roof space of the Hirai house, Kо̄be City. The odachi are connected with penetrating ties (nuki 貫). Note the votive tablets or talismans fixed to the odachi to protect the house.

To accommodate the sericulture that was practised in the hinterlands of Tanba, the large roof space is divided up into multiple floors, and, as illustrated in the section below, the long common rafters (usually taruki 垂木 or 棰, but here called hiso ひそ) that run from the ridge to the wall plates are supported at intermediate points by underpurlins (usually moya 母屋, but here hiso-motase ひそもたせ), which are in turn supported by transverse roof beams; each of these beams is supported by a pair of posts that flank the central odachi. This form of construction is known as torii-gumi, for its resemblance to the Shintо̄ torii gates, whose upper ‘beam’ cantilevers out past its two support posts.

Photo of the roof framing of the Hori house in Kyо̄to Prefecture, taken from the lower attic floor. Visible are two central odachi posts and one of the flanking torii posts on the left.

A section of the Hori house. The central odachi (おだち) is flanked by torii (とりい) posts, making this torii-gumi construction.

Because the odachi in these steeply pitched roofs are long (around five metres or more), they must be braced against buckling or toppling, which is achieved by the addition of two pairs of intermediate oi-sasu (追叉首), which together form a quasi-triangulated structure.

A photo taken from the upper attic floor of an odachi-gumi minka in Tanba. Two pairs of oi-sasu are visible, bracing the long gable-end odachi. Note the adzed finish on the odachi.

The minka in the Kuchi-Tanba (口丹波) region (central Kyо̄to Prefecture) are generally small ‘mountain houses’, but there are many odachi-gumi structures in the area, and simple torii-gumi structures can also be found, as in the Hiraoka house, whose section is shown below.

Hiraoka House in Kuchi-Tanba, Kyо̄to Prefecture. A simple example of torii-gumi (鳥居組) roof framing. Labelled are the crown post (odachi おだち), the torii (鳥居) posts and beams, underpurlins (hiso-motase ひそもたせ) held in the ‘corners’ of the torii, and common rafters (hiso ひそ).

There is also a kind of ‘hybrid’ form of construction where both crown posts (odachi おだち) and principal rafters (sasu 叉首) are present. In the Kawarabatake House in Kyо̄to Prefecture, the central odachi is set plumb, but the two end odachi are slanted outwards towards the gables, and each is crossed with a pair of oi-sasu (追い叉首) running from up from the gable-end wall beams to cross at the ridge to support the ridgepole. These various diagonal members form quasi-triangulated structures which effectively brace the roof longitudinally. Between the points where the oi-sasu meet at the apex are two more pairs of principal rafters, here called hira-sasu (平叉首) because they run down to the long sides of the structure; these sasu also cross at the ridge and triangulate and brace the roof in the transverse direction. This use of odachi and sasu in combination can be found in many regions, and represents an intermediate form of construction in the transition from odachi-gumi to sasu-gumi construction.

Kawarabatake (河原畑) House, Kyо̄to Prefecture. ‘Hybrid’ roof framing utilising both principal rafters (sasu 叉首) and crown posts (odachi, highlighted in black). The two gable-end odachi are slanted outwards, and together with the gable-end principal rafters (oi-sasu 追い叉首) provide effective longitudinal bracing to the structure.

Section of the Kawarabatake House, showing both sasu (叉首) and odachi (おだち).

In the Sako (迫) house in Yoshino (吉野郡), Nara (奈良) Prefecture, the odachi are combined with diagonal sasu (nana-sasu or sha-sasu 斜叉首) to provide tent-like structures at the gable ends for stability in both directions.

Roof framing of the Sako (迫) House in Nara (奈良) Prefecture. Labelled are the crown posts (odachi おだち), ridgepole (munagi 棟木), gable end principal rafters (oi-sasu 追い叉首), long side principal rafters (hira-sasu 平叉首) and diagonal or slanted principal rafters (nana-sasu or sha-sasu 斜叉首), long side wall plates/beams (keta 桁), gable end wall plate/beams (tsuma-hari 妻梁), and longitudinal roof beam (о̄yuka 大床). The odachi are octagonal in section, 30cm in diameter, and 6m long.

The transition in roof framing from odachi-gumi to sasu-gumi roof framing is well illustrated by minka in the mountainous regions of southern О̄saka Prefecture (see section diagrams below). It should be noted that though the final form is classified as sasu-gumi construction, there are no underpurlins (moya 母屋 or yanaka 屋中), and the common rafters (taruki 棰) span clear from ridge to eaves without intermediate support.

Section diagrams of minka in southern О̄saka prefecture showing the transition of roof framing from odachi-gumi (left, here called shin-zuka kо̄hо̄ 真束構法) through hybrid construction (middle) to sasu-gumi construction (right). Note the absence of underpurlins (yanaka 屋中 or moya 母屋) in the sasu-gumi example.

JAPANESE MINKA XXX - ROOF FRAMING 7: ODACHI FRAMING

In the simplest form of traditional Japanese roof framing, shown in the image below, two forked posts known as muna-mochi-bashira (棟持柱, lit. ‘ridge holding post’) hold up a ridgepole (munagi 棟木) at its ends; on this ridgepole are laid common rafters (taruki 垂木) which simply run down to the ground on either side, and the roof, which is the whole of the structure, is thatched.

The simplest tenchikongen-zukuri (天地根元造り) construction, without wall posts or beams, where the rafters terminate at ground level.

With the development of raised-floor (taka-yuka 高床) construction, this basic structure gained walls, with rows of forked posts known as keta-uke-bashira (桁受柱) in the planes of the long walls bearing wall plates or wall beams (keta 桁), which supported the lower ends of the rafters. In both cases, this system of framing is known as tenchikongen-zukuri (天地根元造り).

Two examples of tenchikongen-zukuri in elevation. Top: without walls; bottom: with forked wall posts supporting wall beams.

A simple agricultural structure with two forked muna-mochi-bashira posts holding up a ridgepole and three forked keta-uke-bashira posts supporting the wall plates or wall beams.

A more sophisticated development of this basic system, tenchikongen-no-miya-zukuri (天地根元宮造), can be seen today in some Shinto shrines, and may have been used in the earliest shrines, going back 1,500 years or more. It should be pointed out, however, that there is no definitive archaeological evidence that tenchikongen-zukuri construction was employed in the earliest built structures in Japan, whether residential or religious, and that, according to some sources at least, the method itself may date back only as far as speculative Edo-era reconstructions.

Kamosu Shrine (Kamosu-Jinja 神魂神社), Matsue City, Shimane Prefecture. The building is an example of tenchikongen-no-miya-zukuri; the thick muna-mochi-bashira post can be seen in the gable wall, running from the ground to the ridge and supporting the ridgepole (not visible).

At any rate, common to all these systems are the muna-mochi-bashira posts than run from the ground to the ridge. In minka, these posts are usually known as udatsu-bashira (うだつ柱). In typical minka construction, however, crown posts known as shin-zuka (真束, lit. ‘true post/stump’) have replaced the full-length ground-to-ridge udatsu; shin-zuka start from and are supported by the roof beams, and in turn support the ridgepole. In the Kansai region, these crown posts are called odachi, which is a variant of the word udatsu (in many regions of Kansai, ‘u’ is or was pronounced as ‘o’). Regardless of what these posts might be called in the many other dialects of Japanese, here we will call them odachi (おだち), and the method of framing that employs them odachi-gumi (おだち組). Most commonly seen in the mountainous areas of the Kinki region (basically the same as the Kansai region), but also found in older minka in the Kantо̄ and Tо̄hoku regions, the method is surmised to have had its conception in the primitive roof framing systems discussed above. The shin-zuka usually bear on longitudinal roof beams called jimune (地棟) that cross above the transverse roof beams (koya-gumi-bari (小屋組梁). These jimune are known as nakaoki (中置) or yuki (ゆき).

A simple example of odachi-gumi (おだち組) or shin-zuka-gumi (真束組) construction, showing the relationship between the crown post (odachi おだち), ridgepole (munagi 棟木), longitudinal beam (nakaoki 中置), and transverse beams (koya-bari 小屋梁, unlabelled).

VERNACULAR PICTURES 18

Japanese architecture is far better known as an architecture of timber than of earth or masonry. This lack of earth or masonry buildings can largely be attributed to the threat of earthquakes, as there is no shortage of quality building stone or clay in the country.

Where the consequences of structural failure due to earthquake are not so severe, however, stone and clay are used widely, as in the case of garden walls. In these walls can be seen the same qualities that are characteristic of Japanese craft in general: technical sophistication, close attention to aesthetic effects, a love of material variety and the juxtaposition of ‘high’ and ‘low’, and the tendency to break symmetry or monotony with what for want of a better term might be described as ‘quirks’.

A cob-and-tile garden wall with tile ‘roof’. It is unclear if the variation in this wall is the result of repairs over time or if the striated, folded effect is deliberate, inspired perhaps by rock formations. The contrast between the rustic face of the wall and the refined and ornamented hon-gawara (本瓦) tiling (a style of tiling in which flat nami-hira (並平) and half-round nami-maru )並丸) tiles are alternated) is striking.

A stepped rammed earth wall with tile capping and dry stone footing, complete with drainage ‘tunnel’. Though the rammed earth is the structural material, even these walls have timber posts set into them at intervals, to support their ‘roof’ framing.

VERNACULAR PICTURES 17

A beautiful iron latch on a traditional Japanese storehouse (kura 倉). Unlike half-timbered traditional houses (minka 民家), kura are fully rendered and plastered as a defence against fire.

JAPANESE MINKA XXIX - ROOF FRAMING 6: GASSHO-ZUKURI FRAMING 2

In gasshо̄-zukuri (合掌造り) framing, diagonal bracing members (sujikai 筋違) are known as hagai. The roof structure of the Wakayama House in the Shо̄-gawa region, shown below, is a good illustration of these members. There are the о̄-hagai (大はがい, lit. ‘large hagai’), which, as discussed last week, can be thought of as ‘corner principal rafters’ (sumi-sasu 隅叉首) of a hipped roof (yose-mune-zukuri 寄棟造り) that have been repurposed into major diagonal bracing elements within the gable-roofed gasshо̄-zukuri. They run from the middle section of the ridgepole down to the four corners of the structure. Then there are the ko-hagai (小はがい, lit. ‘small hagai’), slender diagonal members which run between principal rafters to further brace the roof structure against longitudinal lateral forces.

The roof structure of the Wakayama House in the Shо̄-gawa region. The о̄-hagai (大はがい), otherwise known as sumi-gasshо̄ (隅合掌), and ko-hagai (小はがい) are labelled in this gasshо̄-zukuri (合掌造り) roof. The ko-hagai shown are high up near the ridge, but would also be found in the lower part of the roof at the feet of the sasu (principal rafters); presumably they have been omitted for clarity. The dashed lines indicate the external form the roof would take were it a hipped-and-gabled roof, or iri-moya-zukuri (入母屋) in Japanese.

The Wakayama House not a typical example of gasshо̄-zukuri framing, however. Thought to have been built in the early Hо̄reki (宝暦) era (1751 - 1764), it is a rare and extremely valuable survival from the period when the minka of the Shо̄-gawa region were transitioning from hipped roofs to gable roofs, necessitated by the widespread adoption of sericulture in the area. It is thought that the Wakayama House started out as a hipped roof construction, with the gable roof simply being built over it at a later date. This ‘double structure’ gives the roof great stability. The corner and end principal rafters no longer serve as the substructure for purlins (yanaka 屋中), common rafters (taruki 垂木) and thatching, as they would in a hipped roof. One of the end principal rafters (oi-sasu 追い叉首) has further been repurposed as a log ladder (kiza-hashi 刻梯子) by having steps cut into it; this is used to access the upper attic floors.

Whereas the ko-hagai are tenoned diagonally into the long-side principal rafters (hira-sasu 平叉首), the о̄-hagai are often lashed with rope to the principal rafters. Over time as joinery became more sophisticated, the pairs of principal rafters were cross-lapped together at the apex, and in some instances the о̄-hagai developed into a kind of thick penetrating tie that was run through mortises in the principal rafters.

A gasshо̄-zukuri roof in the process of being reassembled, with most of the transverse tie beams (kainagi) in place, and the diagonal ko-hagai clearly visible between the lower halves of the principal rafters (sasu). The pale bands on the principal rafters indicate where the ropes used to tie the purlins (yanaka) to the rafters were.

The same roof fully reassembled and waiting to be thatched. All the transverse members are in place, as are the purlins (yanaka) and rafters (taruki). There are no о̄-hagai on this roof.

Hagai are common in minka built before around 1800 but are not found in minka built more recently than this; instead, thick horizontal penetrating ties (nuki 貫) through the principal rafters are used, just as they are used through the posts in walls. The reason usually given for this change is that advances in techniques for erecting the roof structure made it more logical, but given that hagai are in the planes of the roof faces and therefore present no obstruction to use of the roof space, and also given the obvious structural superiority of diagonal bracing members over horizontal, it does seem to add weight to the idea that the Japanese simply have a deep-seated aesthetic preference for the orthogonal over the diagonal in timber architecture. Regardless, the presence, absence or style of hagai in a minka is one clue available to researchers in estimating its age.

Whereas mortise-and-tenon joints were used in gasshо̄-zukuri framing to connect major structural members such as principal rafters and transverse horizontal ties/beams (kainagi かいなぎ), the purlin — principal rafter and common rafter — purlin connections were only rope-tied. Neso (ネソ, also known as shide-zakura シデザクラ, Amelanchier asiatica) saplings softened by soaking in water were wrapped tightly around the members to be joined; to this joint was added rope made by twisting the bark of the shinanoki (Tilia japonica). Rice straw rope was sometimes used to join members where the loads were not great, but this was not common as rice was not cultivated in the region and so any rice straw used had to be bought from flatland regions.

JAPANESE MINKA XXVIII - ROOF FRAMING 5: GASSHO-ZUKURI FRAMING 1

In this and the next few instalments of this series on roof framing, we will consider gasshо̄-zukuri (合掌造り, lit. ‘praying hands construction’) roof framing, a style of minka found primarily in the basin of the Shо̄ River (Shо̄-gawa 庄川), which flows northwards from the northern part of Gifu Prefecture and though western Toyama prefecture, emptying into Toyama Bay at Takaoka City.

The famed gasshо̄-zukuri minka of Shirakawa-go, Gifu Prefecture.

In principle, gasshо̄-zukuri framing is not very different from the most general type of sasu-gumi (叉首組) construction discussed in previous posts. But as the huge, steeply pitched gasshо̄ roof spaces consist of three, four or even five ‘attic’ levels that are used for raising silkworms, and as sericulture requires good light and ventilation, these roofs must be gabled, with multiple large openings in the gable walls. This is in contrast to the hipped roofs that result from the tripod configuration of typical sasu-gumi framing.

In the region in which gasshо̄-zukuri minka are found, the floor above ground level is known as shita-ni-kai (したニ階, lit. ‘lower second floor’), the floor above that is called the ue-ni-kai (うえ二階, lit. ‘upper second floor’), and the floor above that is the sora-ni-kai (そら二階, lit. ‘sky second floor’). These upper storeys are floored with reeds or timber slats, again to maximise ventilation for the silkworms and their only food, mulberry leaves. It is said that if everything is quiet, the sound of silkworms munching their mulberry leaves on the attic floors above can be heard by the inhabitants on the ground floor.

An upper floor of a gasshо̄-zukuri minka with timber slat flooring.

Diorama showing suspended reed mats holding silkworms and mulberry leaves.

As discussed in a previous post, the lower roof beam framing in gasshо̄-zukuri makes use of bent ‘hockey stick’ beams known as chо̄na-bari (ちょうな梁 or 手斧梁), to account for the height difference between the taller inner jо̄-ya (上屋) or central shu-ya (主屋) posts and the shorter, outer ge-ya (下屋) posts. There is another layer of beams called narashi (ならし) or gasshо̄-bari (合掌梁) over these chо̄na-bari, making the beam framing a two tiered construction.

Cutaway model of a gasshо̄-zukuri minka, clearly showing the chо̄na-bari and three attic floors.

The principal rafters (sasu 叉首) in gasshо̄-zukuri are themselves called gasshо̄, and are particularly magnificent timbers, sometimes 30cm or more square or round; this is necessary both so that they don’t deflect over their long length and for them to be able to carry the large loads from multiple attic floors. To these gasshо̄ are attached intermediate horizontal transverse members called kainagi (かいなぎ) or mizu-bari (水梁, lit. ‘water beam’), which act as both ties to prevent the gasshо̄ spreading or sagging and as beams to support the attic floors.

The uppermost attic floor of a gasshо̄-zukuri minka, partly floored with reed. Note the massive sasu.

It is because of these special characteristics and due to its grand scale that gasshо̄-zukuri framing is classified separately to standard sasu-gumi construction. Recall that in sasu-gumi construction, the principal rafters running from the end of the ridgepole down to the short or ‘gable’ side of the roof are known as oi-sasu (追い叉首, lit. ‘following sasu’; these rafters, together with the corner sasu that make up half of the pyramid structure that gives these roofs their strength against lateral forces, form the end plane of the hipped roof. In some gasshо̄-zukuri, these members may survive somewhat atavistically, concealed within the gabled roof space, as if someone had taken an existing hipped roof and built a gabled roof over top of it, which may be the case. Instead of forming the end plane of a hipped roof as in the sasu-gumi, they serve as diagonal bracing members (sujikai 筋違). What would in a hipped roof be the corner sasu (sumi-sasu 隅叉首, lit. ‘corner principal rafter’) are known in a gabled roof as sumi-gasshо̄ (隅合掌, lit. ‘corner gasshо̄’) or о̄-hagai (大はがい). These members together preserve the triangulating function of the tripod or pyramid framing in the sasu-gumi, and prevent the gasshо̄-zukuri roof from toppling under longitudinal wind or earthquake loads. This method of bracing is only seen in gasshо̄-zukuri and not in other forms of Japanese minka.

Illustration of the peculiar ‘hipped roof within a gable roof’ construction of some gasshо̄-zukuri minka.

VERNACUAR PICTURES 16

No time to write or translate this week, so instead a picture of easily the narrowest street (lane? squeeze?) I’ve ever seen, in Kyoto, Japan. It’s probably only 15cm from gutter to gutter and less than a metre between property boundaries. Obviously from pre-automobile times, it certainly wouldn’t be allowed if proposed today!

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.