In response to a number of observed issues and widespread concerns regarding the dimensional stability of polyisocyanurate (polyiso) roofing insulation, a long-term monitoring study was conducted of a conventional roof assembly in New Westminster, BC. This study was set up to evaluate in-situ conditions which may impact the long-term dimensional stability and thermal performance of two types of polyiso roofing insulation.

The building monitoring program, which included temperature, relative humidity, and displacement sensors, was installed in the roof in 2009 and recorded measurements every 15 minutes for a period of almost 6 years. Results indicate that both types of polyiso roofing insulation shrank during the first two years after installation at a rate independent of temperature. In years three through six, one brand of polyiso continued to shrink, albeit more slowly and with expansion during periods of high temperatures, while the other brand of polyiso stabilized dimensionally.

In addition to its dimensional stability, concerns regarding the long-term thermal performance of polyiso have also been raised by industry, particularly with respect to aging of insulation. The measured results indicate that the conductivity of polyiso insulation is higher at cold temperatures than the standard test conditions, and that field-aged polyiso provides less thermal resistance than the lab-aged polyiso.

RDH Building Science