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.