New 2014 Polyisocyanurate “R” Values

On January 1st, 2014, the Long-Term Thermal Resistance values (LTTR ) or “R” value for polyisocyanurate insulation will be reduced from 6 per inch to 5.6 per inch. To make things more confusing, the “R” value per inch is not consistent. The thicker the insulation, the greater the “R” value per inch. So, 1” polyisocyanurate insulation will have an “R” value of 5.6, where an identical 1.5” sheet will have an “R” value of 5.7 per inch. The following is a table comparing the old “R” values to the new “R” values: One layer of rigid insulation Thickness Prior to 2014 “R” Values After 2014 “R” Values LTTR Value “R” per inch LTTR Value “R” per inch 1” 6.0 6.0 5.6 5.7 1.5” 9.0 6.0 8.6 5.7 2” 12.1 6.1 11.4 5.8 3” 18.5 6.2 17.4 5.8 4” 25.0 6.2 23.6 5.9 Two Layers of rigid insulation “R” Value Prior to 2014 Thickness After 2014 Thickness 15 2 layers of: 1.3” 2 layers of: 1.4” 20 2 layers of: 1.7” 2 layers of: 1.8” 25 2 layers of: 2.1” 2 layers of: 2.2” 30 2 layers of: 2.5” 2 layers of: 2.6” 35 2 layers of: 2.9” 2 layers of: 3.1” 40 2 layers of: 3.3” 2 layers of: 3.5” According to Hunter Panels, one of the leading manufacturers of rigid polyisocyanyurate insulation, the reason […]

“R”=25, The New Rhode Island Flat Roofing Standard

Island Flat Roofing Standard In the middle of 2013, Rhode Island’s “R” value requirements for new flat roof systems changed from a minimum of 20 to a minimum of 25. As before, this only applies to instances where the existing roof system is removed, not situations where a new roof is installed over an existing roof. While many building inspectors in Rhode Island are not yet enforcing the new minimum “R” value requirements, as time marches on, it will become more and more common. And, Massachusetts is talking about enacting the same requirements state wide. To make things more confusing, beginning in 2014, the “R” value of polyisocyanurate insulation, the most common form of rigid insulation used in flat roofing, was decreased due to new testing standards. With the “R” value of insulation going down and the minimum “R” value going up, a decent amount of insulation will need to be added to the roof assembly. Prior to January 1st, 2014, 1 layer of 4” polyisocyanurate insulation was required to meet an “R” value of 25 or 2 layers of 2.1” to achieve the same “R” value. After January 1, 2014, 1 layer of 4.25” polyisocyanurate insulation will be required to meet an “R” value of 25 or 2 layers of 2.2”. Compared to the old minimum “R” value of 20 under the old testing […]