How much insulation does a straw bale house provide?

This will depend on a number of factors, the size of bales (2 or 3 string), whether they wrap the building or are placed between wooden posts, their orientation (on edge or on flat), etc. – but generally speaking, straw has an R-value of 1.45/inch. This means a two string bale laid flat will have an R-value of 27.5. Compare this to R-19, which is the standard for walls in new construction in Canada. R-values simply indicate the thermal conductivity, and thus describe the rate of heat transfer through a material or assembly. The higher the R-value the higher the performing it is.