News From Go Plymouth Foam

The Shrinking R-value of Polyisocyanurate Insulation

What happen to the old days when were told that ISO (Polyisocyanurate) Insulation had an R-Value of 7, 8.3 or 9 per inch. Those days are over! In fact, this last month the “NRCA (National Roofers Contractors Association) has revised its design in-service R-Value recommendation to 5.0 per inch.” (Article)

The real question maybe why? and why another change after last year’s change? The answer is
independent testing. According to research conducted by BSC (Building Science Corporation) and others, “the thermal performance of some insulation materials changes as they age. The R-Value of Polyisocyanurate decreases as some of the gasses … diffuse out and are replaced by air.” This is known by several names - Thermal Drift, Gas Replacement Process or Off Gassing.

Polyiso insulation RValue decreases in colder temperatures

What the research has shown is that unlike EPS (Expanded Polystyrene) Insulation that increases its R-Value when the temperature decreases, ISO Insulation R-Value actually goes down. Bottom line: In the north, when you need the r-value the most, its not there like we thought.

• If you need to use ISO - the BCS Recommendation is to use it in a “hybrid insulation approach” with a cold stable R-Value insulation like EPS.
• Try to substitute out ISO Insulation and use EPS or the New Neopor Plus Insulation.