The thermal expansion and contraction of insulation products within conventional roof assemblies has been identified as a potential performance concern in the roofing industry. This movement can create gaps between insulation boards, which can short-circuit the insulation with respect to heat flow, and in conventional roof assemblies where the insulation also provides the substrate for the roofing membrane, insulation movement can also adversely affect the durability and integrity of the membrane and roofing system. Problems with creasing and ridging of membranes have been observed in the field, along with stress concentrations and holes around fixed penetrations. In particular, field observations have indicated that shrinkage of expanded polystyrene (EPS) insulation products may put undue stress on the roof membranes and could potentially affect the durability of styrene-butadiene-styrene (SBS) roof membranes.
To investigate these industry concerns regarding the potential effect of dimensional movement of EPS insulation on the performance of SBS membranes, laboratory testing was performed on conventional roof specimens in a purpose-built climate chamber. The roof assemblies were cooled and heated to evaluate the amount of insulation movement, and to then observe the impact of these temperature cycles on the roof assembly. This portion of the investigation into this issue focused on re-creation of the observed field condition (e.g., wrinkled membrane), and direct comparison of the relative performance of different insulation types as a first step towards determining the cause of the observed in-service wrinkling.
Presented at the 15th Canadian Conference on Building Science and Technology.