Is Your Roof Insulation Leaking?

By: Tom Huempfner, VP Sales & Marketing – Architectural Products

Huh? Most of us understand insulation is placed in or on a building for thermal protection not moisture protection.  A membrane or cladding material is used to keep the water out.  The reference to “leaking” is a play on words to draw attention to a very important fact that some insulations lose or “leak” R value because of a phenomenon called off-gasing.


There is good news however; if you use expanded polystyrene(EPS) roof insulation you will not “leak” R value.  The R value in EPS comes from trapped air and it is there indefinitely.  Even when EPS has been on the roof for 30 years it has the same R value it had when it was installed. Foam-Control Roof Insulation Tech Bulletin 3011 further discusses the R-Values of roof insulations.  If EPS is in the ground for 15 years and has 5% moisture content it still has 95% of the R value it had when it was in perfect dry condition.  No other rigid foam insulation can make these claims.  Learn more about the 15-year real world study.

NRCA Roof Insulation R-Value RecommendationRecently NRCA (National Roofing Contractors Association) changed the R value of polyisocyanurate insulation to 5 per inch for heating conditions in the 2011 NRCA contractors handbook.

The polyisocyanurate insulation manufacturers continue to advertise an R value of 6 per inch.  Immediately following manufacture polyiso does have a temporary R value of 6 per inch because the polyiso temporarily holds some of the low conductance gas used to push the foam through the extruder.  NRCA has tested polyiso at many different temperatures and the results of these tests show the actual R value for polyiso is lower than the inflated published R value.  It is clear polyiso “leaks” R value.  Architects and contractors need to know the actual R value of the insulation they chose so they do not misinform their customer the building owner or improperly size the HVAC system.

For further evidence that some insulations “leak” R value please review the  manufacturers R value warranties.  The EPS R value warranty is 100% for 20 years.  The polyiso R value warranty is 80% for 10 years. Don’t get soaked because your roof insulation is leaking; buy EPS Roof Insulation.

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3 Responses to Is Your Roof Insulation Leaking?

  1. I.K.Park says:

    there are many Thermal value evaluation But we do not have enbough Data
    which can conversion to R-value (LTTR),if possible what is the basic
    methmatic calculation formula

  2. I.K.Park says:

    R-Value : 2.79 m2’K/W to LTTR (R-value)

    • Mary A. Burk says:

      Good question – unfortunately, there are no conversion metrics for R-Value to LTTR at this point in time. However, we will look into this idea as it could be very beneficial to the industry.

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