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No. 2
1992-06-01
Printable version

VENTILATING ROOFS OVER CATHEDRAL CEILINGS

Cathedral ceilings covered with asphalt shingles require adequate ventilation like any other roof to prevent damage to the shingles. There should be a minimum space of 2 inches between the roof sheathing and the insulation to allow for the unobstructed air movement.

When a vapour barrier is used, cathedral ceilings require a minimum total net area for inlet and outlet vents equivalent to 1/300 of the total ceiling area. Cross ventilation should be ensured by locating half the required vent area at the eave and the other half at the ridge.

If a vapour barrier is not used, then the vent area should be doubled to 1/150 of the total ceiling area.

A typical installation is shown in the following diagram.

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For more information on this subject or other asphalt shingle technical issues, you may contact CASMA by e-mail at casma@casma.ca, or visit our website: www.casma.ca. 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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