By: Jim Nugent, Sales Representative – Architectural Products
I am sure all of you connected to the roofing industry (architects, consultants, contractors and distributors) are well aware of the new lower Polyiso R-Values going into effect in 2014. Some of what is being communicated about these changes could be misunderstood as it relates to EPS Roof Insulation.
First, EPS R-Values are not changing. EPS has the same stable long-term R-Values it has always had. Next, EPS does not need LTTR testing, because EPS R-Values never change. After manufacturing there is virtually no residual blowing agent in EPS. EPS is plastic and trapped air.
EPS has always used the same blowing agent Pentane, which is not ozone depleting. This blowing agent is now being used by Polyiso manufacturers.
The manufacturing process for Polyiso insulation traps their blowing agent in the cell structure of the foam. The blowing agent is a slightly better insulator than air. However, it is very difficult to predict how quickly the blowing agent will leave the product and be replaced with air. That is the reason for the development of LTTR testing several years ago.
As a way to eliminate some of the confusion regarding R-values, I would suggest you ask this question of your contact with the manufactures of rigid foam insulation; “What would be the R-value of their product if their foam cells only contained air?” An insulation that only relies on air for it’s R-value is a product you could rely on forever. Here is a hint… 20-25 psi EPS, XPS and Polyiso would all be about 4.8 – 5.0 per inch at 40 degree mean temperature.
A valuable article in the Construction Specifier August 2012 magazine further explains these points and is a great read for anyone wanting to fully understand the R-value discussion.