Closed-cell foam insulation is used in all of our tiny houses. There are many advantages such as an increased efficiency, rigidity and less degradation over time compared to fiberglass insulation.
We apply 3 inches in the ceiling cavities, 2 inches in the walls and 2 inches beneath the subfloor.
Below is a guide to the R-Value of insulation:
1 inch of closed-cell insulation = R7
3 inches in ceiling = R21
2 inches in walls = R14
2 inches in floor = R14
FYI » Open-cell insulation has an R-Value of R3.5 per inch.