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Insulating Your Tiny House With Rigid Foam Panels

Insulating Your Tiny House With Rigid Foam Panels

2/19/15 (6 years ago)

Insulating Your Tiny House With Rigid Foam Panels

When you build your tiny house on wheels you quickly realize that your walls and ceiling are really thin compared to a "real" house. Since we used steel studs our walls are only 2-1/2" thick. So, we needed to get the most out of our insulation choice. We also saw it is a challenge to make our walls/ceiling/floors as light and rigid as possible. When we looked at our options we chose Expanded Polystyrene (EPS) foam panels with an added radiant heat barrier foil. This product typically has an R value of 3.6 to 4.0 per inch of thickness so our total R value for our Big Tiny House insulation is around 10. The reflective coating probably won't add much, since it needs to be exposed to the air in order to radiate the heat effectively.

In addition, we decided to use wood furring strips (lighter than metal) attached to the steel studs over a Tyvec vapor barrier to decrease thermal transfer. Also, noise pollution is kept to a minimum with this air gap or "rain screen" design. We chose metal (steel) siding and roofing that came with a paint coating called Dura Tech that reflects heat. We had over 100 degree weather over the summer and the trailer stayed nice and cool. 

Here are some advantages and disadvantages of our choice of insulation.

Advantages of Rigid Foam Insulation Panels

  • Used EPS (expanded polystyrene) instead of XPS (extruded polystyrene) or ISO (polyisocyanurate). Not as rigid and about 20% less insulating (4R per inch instead of 5R per inch) but at least 30% cheaper.

  • Rigid foam offers very high R-values compared to loose-fill insulation, and some of the best among foam options. Ratings range from R-4 to R-6.5 per inch, even without a foil facing to improve matters.

  • Expanded polystyrene board is the only type which does not use HCFCs in its production, so is the greenest choice.

  • EPS can be bought with a radiant heat barrier facing foil that will significantly improve the insulating properties by reflecting infrared solar energy before penetrating the wall or ceiling.

  • Rigid foam, due to its structure and its installation method, will help your walls become stronger than they were before it was installed which is an added bonus when you are using metal studs for your tiny home.

  • High R-value per inch: useful where space is tight or cramped, such as in a tiny home.

  • All are lightweight and strong, although EPS can be a little crumbly.

  • Provides acoustic insulation which is very important when your walls/floors/ceiling are so thin.

  • Most are easily cut with utility knives and power saws.

  • All are water resistant, some more so than others (but none should face prolonged exposure to water).

  • Will not rot.

Disadvantages of Rigid Foam Insulation

  • Rigid foam insulation in wall cavities must be tightly fitted to stop air infiltration. We notched our panels on one edge in order to fill the gap in the metal studs and then generously used construction adhesive on the other edge to adhere to the next metal stud. After completing the walls, we went over every seam and where there was an air gap, we would fill it with spray foam insulation.

  • Rigid foam is susceptible to sunlight. UV rays damage it, so don't expose it to the sun for long periods of time. This means that you need to side your house soon after insulating it.

  • The air bubbles inside expanded polystyrene board stop heat transfer but can accumulate moisture and thus become ineffective. A moisture barrier is needed on the side exposed to the outside air. We used a generic equivalent to Tyvec.

Tools Used

  • (2) tables saws for cutting and notching foam panels

  • Putty knife (for levering in stubborn foam panels into tracks)

  • Hand saw (for "precision" custom cuts in foam panels)

  • Liquid Nails Heavy Duty (for gluing foam panels to tracks/studs)

  • Liquid Nails Panel & Foam (for gluing foam panels together)

  • 10 oz. and 28 oz. caulk guns

Alternatives to Rigid Foam Insulation Panels

Our choice of using this particular insulation was based on our unique build. Many choose to use spray foam insulation which is great if you can afford it and you have plywood sheeting on the outside layer of your home to enclose the foam as it expands.

Others prefer fiberglass insulation, but again it is made for a traditional wall depth and width so make sure it will work for your design. We, on the other hand, don't have thick walls or plywood sheeting in our design in order to save weight so the rigid foam panels were our best insulation option for our tiny house on wheels.

View our photos of the wall panel phase of construction ›