mildew and mold growth. The straw-clay mixture is poured into wall cavities (and ceiling cavities if desired) and left to dry.

The down-side of straw insulation – apart from the fire hazards which must be considered and countered as outlined above – is the weight of the materials. A three-string straw bale weighs around 90 pounds (40 kilos), so putting a lot of them inside walls or ceilings is a real challenge. Your house framing will need serious reinforcement to tackle that kind of load, especially if you intend to insulate the ceilings with straw bales, and this increases construction costs.

Vapor barriers

If you decide to go for natural insulation, you must not install a vapor barrier. Such a barrier increases the moisture retention in the insulation, which will lead to problems of mildew, mold, and eventual rotting in timbers and framing.

Natural materials need to breathe. Use breathable plasters to allow moisture to escape the insulation and ensure that no vapor barrier is installed.