The raised floor, or taka-yuka (高床), refers to the arrangement where the plane of the ‘living floor’ is raised above the ground level. It can describe not only the floors of residential dwellings but also those of granaries and storehouses (these non-residential structures were likely the earliest examples of the taka-yuka, due to their obvious advantages in preserving grain and other perishables from rot and vermin); it may also refer to the subtype of earthen-floored dwellings covered in last week’s post, where an earth podium is built up well above the natural ground level. Here, however, we will be primarily discussing what most people understand by the term taka-yuka: a timber floor structure of stumps, bearers and joists, with a subfloor void between the floor and the ground.

In Japan, raised floors are typically 400 to 500mm above ground level, though there are examples of floors up to a metre off the ground. Historically they have been most commonly associated with and found amongst the residences of the aristocratic and upper classes, in low-lying marshy areas and wetlands, and in the warmer and more humid regions of the country, from southern Honshū to Okinawa.

The most common floor framing (yuka-gumi 床組) construction system in modern Japanese timber-framed houses, at least until relatively recent times, is this: 90 x 90mm bearers (о̄biki 大引) spanning the area within the ground sills (dodai 土台) are laid down at a pitch (spacing) of 910mm, on timber stumps (yuka-zuka 床束) that are also 90 x 90mm in section and set at a pitch of 910mm. These stumps are tied together near their bases with thin ties (ne-garami nuki 根がらみ貫) of around 90 x 12mm, whose purpose is to prevent the stumps from slipping off their pads. To brace the floor structure in the horizontal plane, diagonal 90 x 90mm members called hi-uchi dodai (火打ち土台) are inserted in the internal corners and in other locations, in the same plane as the dodai and о̄biki. On top of and perpendicular to the bearers are laid joists (neda 根太) of around 45 x 45mm or 60 x 45mm, at a pitch of either 455mm or 303mm, depending on the floor covering/load and the strength and depth of the member. Joists are doubled under internal walls. In minka, tatami mats were usually only laid in the formal zashiki room; in this case, joist spacing was the closer 303mm, because the thin subfloor boards typically used under tatami can’t span the 455mm between joists that the 20mm-30mm thick finish floorboards used elsewhere can.

Diagram showing the elements of modern Japanese floor construction.

Rip saws (oga 大鋸) did not appear in Japan until the 14th century, and spread only slowly.

A print from the 1830s depicting men cutting a large section timber with an *oga.*

Before that, the only way boards and planks could be made was by splitting logs longitudinally with wedges, then finishing the surface with an adze (chо̄na 釿) or spear plane (yari-ganna 槍鉋).

Relatively ready availability of large section timbers, practical limits to how thinly logs could be split, and the labour involved in finishing the boards all meant that this method tended to produce thicker planks. Adze-finished timbers have a beautiful undulating, wavelike finish, and genuinely adzed floorboards are still an option today the for those with the money; for those without, machine-finished ‘mock-adzed’ floorboards are also available.