The smoke and soot from the irori rise into the rafters, helping to keep the roof thatching dry and to drive out insects. This helps to preserve both the thatch and the wooden pillars and beams.

囲炉裏から出る煙とすすは、茅葺き屋根を乾燥させると同時に、虫よけの効果もあり、茅や木の柱と梁を長持ちさせました。