Technical Bulletin #33
Current as of October 2013
For many years, conventional roof installations and building codes have required a ventilated attic space beneath the roof. The benefits of a ventilated space beneath the shingled roof deck are numerous, but primarily include moisture control and roof surface temperature moderation.
In recent years some organizations have promoted what are known as "hot roofs" – roofs in which the insulation is sprayed or affixed immediately to the underside of the roof deck. The term "hot roofs" is appropriate since the shingled roof system, without the moderating air movement beneath it, can become very hot.
Experience has shown that shingled roofs deteriorate at a faster rate when roof top temperatures are higher. In fact, a common laboratory test method used to simulate accelerated aging merely places the shingle samples in a hot oven, since heat is a key mechanism of aging.
It is admirable that building owners and homebuilders are increasing residential insulation, as energy savings can be realized. However, CASMA recommends that the insulation should not be placed in immediate contact with the underside of the roof deck. Rather, a ventilation space, or channels should be provided, with air intake at the lower part of the roof (soffit) and exhausted at or near the top of the roof as practical.
Homeowners are encouraged to confirm ventilation requirements by consulting the applicable local building code, the Canadian Standard's Association roofing standards, and the shingle manufacturer's shingle installation instructions and limited warranty requirements. See also CASMA Technical Bulletins # 1 and # 2 for more information and recommendations regarding proper roof ventilation.
The information contained in this bulletin is for general education and is not intended to replace advice from a qualified contractor or direction on usage/installation from the manufacturer. Consumers should be aware of the safety hazards associated with work on roofs and, before doing so themselves, should consider following CASMA s advice of using qualified contractors. This bulletin may be reproduced with permission on condition that it be reproduced in whole, unedited, with attribution of copyright to CASMA.
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