Impact of Material Dimensional Stability on Conventional Roof Performance


Did you know that the wrinkles observed on SBS-modified bitumen roofing membranes are often due to the type of insulation used underneath?

Indeed, this kind of wrinkle is often related to the presence of expanded polystyrene insulation underneath the membrane in conventional roof assemblies. In such assemblies, the insulation can be exposed to high temperatures, so high that gaps can appear between the insulation panels as well as between the insulation panels and the parapets.

Download this ebook explaining in detail the connection between the wrinkling of roof membranes and the dimensional stability of materials, written by Jun Tatara and Lorne Ricketts of RDH Building Science, Inc.


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  • Understanding the difference between thermal expansion and dimensional stability.
  • Recognizing that different types of roof insulating materials have varying levels of dimensional stability.
  • Knowing that instability of insulation can lead to permanent deformation of the roof membrane.

*This research was presented at the 15th Canadian Conference on Building Science and Technology in Vancouver in November 2017, as well as at the 2018 RCI International Convention in Houston in March.

Image showing a gap between two insulation panels, which causes thermal bridges.

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