Tips for choosing the best spray foam for the job
The editors from Fine Homebuilding and Green Building Advisor recently published a Spray Foam Tip Sheet for anyone considering the use of spray foam insulation in a residential or commercial application. For anyone considering using this energy efficient material, here are some tips to consider when determining which spray foam type to use - open cell or closed cell.
Open cell spray foam is permeable to moisture and impermeable to air, which can be a virtue or a drawback, depending on the application. Although open cell spray foam costs less than closed cell spray foam, it has a lower R-value* per inch, so a thicker layer is required. If the framing members are deep enough to accomodate your required R-value*, open cell spray foam may end up costing less. Open cell spray foam has a benign blowing agent (water); because the blowing agent used in most closed-cell spray foams has a very high global warming potential, many green builders prefer open cell spray foam to closed cell spray foam for this reason.
- R-value* per inch: approx. 3.6
- Cost: approx. $0.44 to $0.65 per board foot**
Closed cell spray foam performs better than any other insulation. It is impervious to moisture, and it's an effective vapor retarder. It is also an excellent air barrier. Closed cell spray foam can be used under slabs, on below-grade or above-grade walls, in ceilings, or even roofing. Because of its density and glue-like tenacity, it also adds racking strength to a wall (ideal for hurricane prone areas), ceiling or roof assembly. Its disadvantages include a larger initial investment and the use of blowing agents with a higher global warming potential.
- R-value per inch: approx. 6.5*
- Cost: approx. $0.70 to $1 per board foot**
**Cost estimates are subject to various factors and a licensed Icynene spray foam contractor will be able to give you a more accurate cost for each spray foam application.
* R means resistance to heat flow. The higher the R-value, the greater the insulating power. Compare insulation R-values before you buy. There are other factors to consider. The amount of insulation you need depends mainly on the climate you live in. Also, your fuel savings from insulation will depend upon the climate, the type and size of your house, the amount of insulation already in your house, and your fuel use patterns and family size. If you buy too much insulation, it will cost you more than what you'll save on fuel. To get the marked R-value, it is essential that this insulation be installed properly.