RE: Ventilation requirements for roof spaces Ontario Building Code, (OBC) Subsection 9.19.
According to Subsection 9.19. of the OBC, ventilation must be provided to all roof or attic spaces. This requirement is intended to provide adequate air circulation in order to avoid air being trapped and condensed. However, it is the opinion of the Housing Development & Buildings Branch that, where a roof assembly is filled with rigid insulation (no gaps or empty space in between), Subsection 9.19. of the OBC need not apply and may be considered to be acceptable under sufficiency of compliance in Section 2.7 of the OBC. This opinion is based on the fact that, if a roof assembly does not contain any air space or air pockets in between, air will not turn into vapour and condense within such an assembly even under extreme weather condition.
May 1997
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