By: John Cowan, Regional Sales Manager
I recently had the opportunity to participate in a series of training seminars sponsored by a major commercial single ply membrane roofing manufacturer. It was impressive as they discussed the addition of several membrane warranties; bringing the total number up to 17. We then moved on to discussion about roof insulation…
Both Polyiso (ISO) and EPS roof insulation were featured. Starting first with Polyiso, we examined ISO’s R-Value, which is advertised as R-6 per inch, although the NRCA has recommended using R-5.6 per inch since 1987. Then in December 2010, NRCA’s associate technical director released a revised recommendation for Polyiso’s R-Value. His recommendation for the in-service R-value is R-5.0 per inch in heating conditions and R-5.6 per inch in cooling conditions. This is puzzling, because ISO manufacturers claim R-6 per inch based on LTTR. LTTR stands for Long Term Thermal Resistance; a complicated weighted average that has nothing to do with actual performance.
We then examined the insulation warranties. Has anyone seen a warranty for Polyiso? It’s very confusing, like their R-value, and it doesn’t offer the coverage one might expect. However, the R-value warranty for EPS roof insulation is very clear. A 100% written warranty against any loss of thermal performance and it includes documentation showing the performance after 20 years. ISO warranties 80% of R-6 LTTR and only guarantees that it does not drop below R-4.8 per inch. This is THEIR warranty. You tell me what their thermal performance really is and what design values to actually use? I should be the expert with this, yet I have to admit I find the with the Polyiso R-values and warranty coverage information confusing, so how can anyone else understand it?
WHO NEEDS A WARRANTY ANYWAY if a product doesn’t provide the actual benefit that it has been promoted to do? When buildings account for nearly 40% of all energy use and CO2 emissions in the country, the building owner paying the energy bills for the next 20-years should be concerned that they purchased something that is not performing as intended. Since no one can figure out this polyiso r-value/warranty mess, my vote goes to EPS roof insulation. The r-value remains the same from the first day it is manufactured throughout its lifetime and it has a straight-forward warranty. I know exactly what I have purchased.
