EPS vs. Polyiso: A Climate Change for Roof Insulation

DENVER, CO--(Marketwire - Oct 9, 2012) - ACH Foam Technologies applauded the decision by the National Roofing Contractors Association (NRCA) to revise the R-value of polyisocyanurate (ISO) insulation. In The NRCA Roofing Manual: Membrane Roof Systems - 2011, NRCA updated its design R-value recommendations for polyiso, taking into account polyiso's loss of R-value as the material voluntarily emits low conductance gas after it is manufactured.

ACH Foam Technologies is a major manufacturer of Expanded Polystyrene (EPS) roof insulation. According to Tom Huempfner, Vice President, confusion has existed about the actual in-service R-value of polyiso (ISO) when used as insulation in roof systems.

"EPS retains 100% of its published R-value for 20 years. In comparison, the polyiso warranty is only for 80% of the published R-value for 10 years. Building owners who are paying the energy bills and design professionals who size HVAC equipment should be aware of this very important information," explains Huempfner.

Mark S. Graham, NRCA's Associate Executive Director of Technical Services, makes clear the issue of changing R-values: "In 2009, NRCA conducted R-value testing at various temperatures. NRCA's testing of polyisocyanurate insulation at 25F, 40F, 75F and 110F showed actual R-values less than LTTR values."*

Graham continues, "Although the LTTR method of R-value determination and reporting may be appropriate for laboratory analysis, research comparison and procurement purposes, NRCA does not consider LTTR use to be appropriate for roof system design purposes when actual in-service R-value can be an important aspect of roof system performance."

NRCA's 2011 manual recommends designers using polyisocyanurate insulation determine thermal insulation requirements using an in-service R-value of 5.0 per inch thickness in heating conditions and 5.6 per inch thickness in cooling conditions. NRCA also recommends designers specify polyisocyuanurate by its desired thickness -- not its R-value -- to avoid possible confusion during procurement.

Cost & R-Value Warranty Analysis:
Insulation   R-25 Thickness   R-25 Cost* Square Foot   Warranty
(% of Published R-Value)
  Warranty Term
Type II EPS   5.50"   $1.20/SF   100%   20 Years
Type 2 ISO   5.00"   $1.60/SF   80%   10 Years
Type IV XPS   5.00"   $1.80/SF   90%   15 Years
*As of October 2012. Subject to current & location pricing.

For the complete NRCA report visit http://www.achfoam.com/media/docs/Roofing/Roofing%203001.pdf. For more information about EPS Roof Insulation visit http://www.achfoam.com/RoofInsulation.aspx

*Taken from an article written by Graham and published in December 2010 on Professionalroofing.net.