How to properly insulate a tiny house

Spray-in-place polyurethane is the only commonly used solid insulation that absolutely protects itself from air infiltration. When it is properly placed between two studs or against a concrete block wall or wherever, the bonding of the spray plus the expansion of the material in place creates a total seal. It’s almost impossible to overestimate this total seal. In my opinion, most of the heat loss in the walls of a home has to do with the seal, rather than the insulation.

Heat does not conduct horizontally nearly as well as it does vertically. Therefore, if a home had no insulation in its walls, but did have an absolute airtight seal, there would not necessarily be a huge difference in heat loss. But this would not be the case if ceiling insulation was missing.

Spray-in-place polyurethane can most effectively stop air infiltration. It is the only material that properly applied fills in the corners, cripples, double studs, bottom plates, top plates, etc. The R-value of a material is of no interest or consequence if air can get past it.

Reference to additional information on foam insulation

3 inches of foam insulation is plenty

Nearly 100% of the heat loss from air infiltration is stopped with the first one-fourth of an inch of urethane foam. The second inch of spray-in-place urethane stops about 90% of heat loss, and the third inch stops about 95% and so forth.

We sprayed all sides of our substructure. Subfloor, all 4 walls, and the ceiling. This creates an airtight building envelope which will dramatically reduce heat loss.

We even boxed in the wheel wells and applied 3″ of foam here too.

Our wall sheathing was applied vertically using 10′ panels to minimize the horizontal seams around the building

We even sprayed the entire ceiling