Insulation decides whether a tiny home is comfortable or miserable, and it is one of the hardest things to fix after the build is finished. The three main options, spray foam, sheep's wool, and rigid board, all work, but they differ in cost, installation, moisture behavior, and how they handle the tight wall cavities of a tiny house.

Closed-cell spray foam is the best-performing option for most tiny homes. It fills every gap, creates an airtight seal, and adds structural rigidity, all at about R-6.5 per inch. A two-inch layer in a standard wall gives around R-13, and it doubles as a vapor barrier, which matters in a small, humid home. The downsides are cost, around 1 to 2 dollars per square foot per inch installed, and the fact that it is difficult to remove if you ever need to access wiring or plumbing inside the wall.

Sheep's wool is the natural alternative. It insulates at about R-3.5 per inch, absorbs and releases moisture without losing performance, and is safe to handle without protective gear. It is also one of the few insulation materials that actually improves indoor air quality. The trade-offs are thickness: you need more of it to reach the same R-value, and cost, which is higher than fiberglass but lower than spray foam.

Rigid foam board, like polyisocyanurate, delivers the highest R-value per inch, around R-6.5, in a precise, cut-to-fit panel. It works well in floors and roofs, where you can layer it without gaps. In walls, the challenge is sealing the edges: every gap is a thermal bridge, so board must be paired with careful taping or a layer of spray foam to seal the seams.

Moisture is the real enemy in a tiny home. Cooking, showering, and breathing produce a lot of water vapor in a small volume, and the wrong insulation traps it. Whatever material you choose, pair it with a proper vapor barrier on the warm side, a vent fan in the bathroom and kitchen, and a way for the wall to dry. Condensation inside a wall causes mold long before you notice it.

For most builders, closed-cell spray foam in the walls and roof is the simplest reliable choice. For a natural build, sheep's wool with a smart vapor barrier works well if you have the wall depth. For a floor, rigid board is hard to beat. Whatever you choose, insulate once and insulate well: it is far cheaper than heating a leaky home for the next twenty years.

The floor and roof lose more heat than the walls, and they are the easiest places to get insulation wrong. For the floor, rigid foam board between the joists works well, but you must seal every gap, because cold air rising through the floor is the most common complaint in a tiny home. A layer of spray foam under the floor, or a continuous sheet of rigid board below the joists, closes the gaps that batts leave behind. Skirting around the base of a tiny house on wheels also helps enormously by blocking wind from under the floor.

The roof needs the most insulation of all, because hot air rises and heat escapes upward. Aim for R-30 or better in the roof, which usually means a combination of spray foam and rigid board, or a deep cavity filled with wool. Ventilation matters here too: a vented roof assembly, with an air gap between the insulation and the roof deck, lets moisture escape and prevents the condensation that causes rot. A tiny home with a well-insulated roof and a poorly insulated floor will still feel cold, so treat the whole envelope as one system, not a set of separate parts.