The roofs all face the same way, around the fields. Ainokura is a mountain settlement where more than twenty gasshō-zukuri farmhouses survive, arranged around the paddy with their gable ends aligned. The roofs are steeply pitched so that snow slides off rather than accumulating, and the space that pitch creates under the thatch is not attic storage but working floor, used for rearing silkworms and for the other indoor work of a long winter.

The consistent orientation is generally explained by wind and light: the direction the weather moves through the valley, and where the sun falls at the times of year it matters. Ainokura was designated an Important Preservation District in December 1994, and from the high ground above the village the whole run of thatched roofs can be seen at once. With only twenty-odd households, houses rarely come empty here. The centre of Nanto is about forty minutes away by car, which is the practical measure of how remote the valley is.

A thatched roof is replaced entirely every few decades. The quantity of material and labour involved is far beyond one household, so the work is done by assembling the whole settlement and taking the houses in turn — which means the number of houses sets the interval at which any given roof comes round again. Twenty is not an arbitrary figure. It is close to the smallest number of households that can keep such a rotation running at all, which is another way of saying that the village and the roofs require each other in order to continue. Lose four or five houses and the arithmetic stops working for the rest.