土壁の家に住む——古民家の調湿と手入れの知恵Living in a house of earthen walls — a kominka's breathing and its care
古民家の部屋に入ると、夏でもどこかひんやりと、じめつかない空気を感じることがあります。その多くは、土壁のはたらきによるものです。土に藁（わら）や砂を混ぜ、竹を編んだ下地に塗り重ねた壁は、空気中の水分を吸ったり放したりしながら、室内の湿度をゆるやかに整えてくれます。梅雨どきの湿気を吸い、乾いた季節にはそれを返す——土壁は、いわば呼吸する壁です。
この調湿のはたらきは、壁の表面が塗料などで覆われていないからこそ保たれます。だからこそ、土壁の家では日々の付き合い方が大切になります。まずは風を通すこと。晴れた日に窓や障子を開けて空気を動かすだけで、壁は湿気をため込みにくくなります。家具を壁にぴったり寄せず、少し隙間をあけておくのも、目立たないけれど効く工夫です。
土壁は、傷んでも直せるのが強みです。地震や乾燥で細かなひび（貫割れ）が入ったり、角が欠けたりしても、土や漆喰で部分的に埋め、塗り直すことができます。全面を張り替えなくても、傷んだところだけ手を入れていける——これが土壁の手入れの基本です。ひびを見つけたら、まずは大きさと深さを見て、表面だけなら急がず様子を見る。深く広がるようなら、左官の職人に相談するのが安心です。土壁の家に住むとは、この小さな手入れを季節ごとに重ねていくこと。手をかけるほど、家は静かに応えてくれます。Step into a room in an old Japanese house and, even in summer, you may sense a coolness in the air, a dryness to it. Much of this is the work of the earthen walls. Made of earth mixed with straw and sand, plastered in layers over a woven bamboo lattice, these walls take in and release the moisture of the air, gently keeping the room's humidity in balance. They drink in the damp of the rainy season and give it back when the air turns dry — an earthen wall is, you might say, a wall that breathes.
This regulating power survives precisely because the wall's surface is not sealed under paint. That is why, in a house of earthen walls, the day-to-day relationship with them matters. First, let the air move. Simply opening the windows and shoji on a fine day keeps the walls from holding onto damp. Not pushing furniture flush against the wall, but leaving a small gap, is another quiet measure that works.
An earthen wall's strength is that it can be repaired when it wears. Fine cracks from an earthquake or dryness, or a chipped corner, can be filled in part with earth or plaster and re-coated. You need not replace the whole surface — tending only where it is damaged is the basis of earthen-wall care. When you find a crack, first look at its size and depth; if it is only on the surface, there is no need to rush. If it runs deep and spreads, it is safest to consult a plasterer. To live in a house of earthen walls is to layer these small acts of care season by season. The more you tend it, the more quietly the house answers back.