An addendum of sorts to the previous post on koushi:

An important characteristic of the machiya facade is the subtle stepping-back in depth or ‘reveals’ (mikomi, 見込み) of the various members: posts to sills, posts to plaster infill, koushi perimeter frame to horizontals, horizontals to verticals, etc. These reveals are only on the order of 10-20mm or so, but they impart subtle variety and visual interest to the facade, giving it depth, shadow, and life. The rhythm of the facade is played not only along the x or left-right axis, but also along the z or front-back axis. This has its analogue in traditional Western brick facades, which achieved similar effects by stepping courses and rows of brick in and out to form cornices, string courses, pilasters and the like- again, variations of only a few centimetres are enough to bring the facade to life. This is in contrast to the modern industrial predilection for ‘flush’ surfaces, and the resulting over-compensation of planning schemes in demanding exagerrated setbacks in the facade on the order of metres, as I have written about in an earlier post.

The stepping-back also appeals to structural logic: primary members are foremost, with subsequent members set back according to structural importance.

Finally, mikomi gives thought to the carpenter or joiner. If all members are designed flush, there is no tolerance: any error is glaring. But if, for example, a beam or header rail is tenoned into a post with a designed mikomi of 10mm, an error of a millimetre or two either way will be unnoticeable.