2lb Spray Foam Insulation - Medium Density/Closed Cell
2 lb spray foam, when applied at a thickness of 50mm or more, can act as a vapour barrier. They offer the highest R value per inch of all spray foam systems (typically R5.5-6 per inch depending on the thickness).
They also contribute to the structural strength of an assembly in addition to helping to provide a high performance building envelope.
The high compressive strength makes 2 lb density foams ideal for below grade foundation insulations providing a waterproof insulating blanket on the exterior of the concrete.
A NOTE ON R VALUES WITH MEDIUM DENSITY 2 LB SPRAY FOAMS:
2 lb spray foams rely on a captive blowing agent contained in the closed cell structure to give them a higher R value. Over time some of the blowing agent in the cells near the surface of the foam escapes into the environment and is replaced by air. This exchange reduces the R value of 2 lb foams over time. Initial R values for most spray foams are over R 7 per inch at time of installation but drop quickly over time because of the release of the refrigerant gas (HFC 245fa) contained in the cells. (See our page on Light Density, ½ lb spray foam)
Many contractors blatantly misrepresent the R value of 2 lb foams. In Canada there is a far more stringent test protocol than in the US. Spray foam contractors and manufacturers in Canada are required to state their R value test results using the CAN/ULC S 770 test method. This is known as the Long Term Thermal Resistance (LTTR) test. Using this protocol, no medium density spray foam has tested to an R value greater than R6 per inch. Some less scrupulous contractors will quote US test data using “aged R value” as per an ASTM C518 test which will show R values of up to R7 per inch. The Canadian Urethane Foam Contractors Association (CUFCA) has mandated that their contractors use the LTTR R values when promoting their products.
Think about it. Are you getting the true story from your contractor? If they give you 3” of spray foam and tell you it is R20 or R21, we are quoting 3.5” to give you the same R value. The unscrupulous contractor is using 15% less foam!! There’s a reason they are cheaper. Would you want to do business with a contractor like that?
Do your homework and ask what the LTTR is for the product you’re being quoted on.
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