Did you know that polyisocynaurate insulation is one of the most commonly used insulation types in the roofing industry?  When the building code agencies adopt the 2012 ASHRAE the prescribed R-values for above deck roof insulation will be increasing again.   There is some questions on how long-term thermal resistance (LTTR) should be used for R- Value determination.  NRCA recommends using an in-service of 5.0 per inch thickness in heating conditions and 5.6 per inch thickness in cooling conditions in determining thermal calculations. Be aware that there are different factors to consider when working with metal fasteners.  To read the complete article by Darrell Smith, PE, RRC is Civil Engineer – Building Envelope/Roof Consultant, visit the Buildings website at http://bit.ly/PIfDFd.  You will also find information providing the R-Value recommendations based on the Zones you are working in.  Northern Michigan is in Zone 6 & 7, with Southern Michigan in Zone 5.

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