Hundreds of years ago the highlands of Scotland and Ireland were dotted with a type of dwelling called blackhouses. These were long narrow buildings, often laid in parallel to other blackhouses, with dry-stone walls and thatched roofs rendered black with soot. The smoke came from a peat fire that was lit at all times in the center of the kitchen and living area. As appalling as it sounds, the houses had no chimneys and very small windows leading to a suffocating accumulation of smoke inside. The smoke escaped through the porous roof, slowly blackening the turf or straw in the process.

The smoke killed bugs living in the roof. Smoked thatch was also considered an excellent fertilizer. So every year, the roof was stripped down and the blackened thatch used to fertilize their fields, while the roof was rethatched to supply for next year.

Blackhouses in Gearrannan, Isle of Lewis. Photo credit: Iñaki Barrutiabengoa/Panoramio