In January 2014 we sent a newsletter discussing newly posted  LTTR values (R-value) resulting from revised testing criteria. According to the National Roofing Contractors Association (NRCA) the R value of 1″ of polyisocyanurate insulation has dropped once again effective January 2016.
Why the change?
This is the result of applying the newest test methods to insulation boards of varying temperatures.  Apparently boards at colder temperatures provide higher R values than boards at warmer temperatures. NRCA has chosen to refer to the lowest common denominator when listing new R values.  Below is a breakdown of changes by year.
2013: 1″ of polyisocyanurate = R6
2014 & 2015: 1″ of polyisocyanurate = R5.7
2016: 1″ of polyisocyanurate = R5.0
How does this effect you? 
Most local building codes require an insulation package meeting R20 whenever a new roof system is installed. In 2014 & 2015 only 3.5″ of polyisocyanurate insulation was required to satisfy the R20 requirement.  In 2016, 4″ of polyisocyanurate insulation will be required to meet the R20 requirement. Additionally, the new roof height will be reducing flashings heights by 1/2″.  This may result in additional work required to meet industry standard 8″ minimum flashing heights. Ultimately these factors will result in more material & associated costs for future roof replacements.

We hope you find this information helpful.  Contact us to discuss how this may effect your future projects.

Project Consultant
(314) 687-5687