Typical residential house construction in North America has long had vented attics above living space with the insulation and air control layer at the ceiling plane of the living space. Except for documented wintertime condensation issues in cold climates, such vented attics generally perform quite well, provided that they are ventilated adequately and air leakage from the interior is prevented. However, architects and designers are moving away from empty attics by using the attic space as conditioned storage or bonus rooms, or by designing larger interior volumes with cathedral ceilings. The practical challenges of ventilating cathedralized attics and cathedral ceilings have been significant, both because of increased geometrical complexity and because of the number of penetrations typically required for services.
Spray foam has been used successfully in tens of thousands of unvented roof assemblies throughout North America but some concerns remain in the building industry that these assemblies are inferior to ventilated roof assemblies. The National Building Code of Canada, in particular, makes it difficult for designers to use unvented roof assemblies, even using designs that are approved in similar building codes in the United States and have been proven to be durable, high-performing options. Over the past decade, the authors have been directly involved with studies of both 0.5 pcf (8 kg/m3) open cell spray foam, and 2.0 pcf (32 kg/m3) closed cell spray foam in unvented roof assemblies in various climates with continuous monitoring of temperature and moisture conditions. This paper provides a literature review of research that has been conducted on wood-framed sloped unvented roof assemblies, but will focus on results from a field monitoring study of sloped unvented wood roofs in partnership with the University of Waterloo, as well as a field survey that opened roofs and removed samples from aged unvented roof assemblies.
Presented at the 15th Canadian Conference on Building Science and Technology.