Ask Jon Eakes

Last Updated: Friday, October 15th, 1999, Created: Friday, October 15th, 1999

HOW DO I VENTILATE A CATHEDRAL CEILING?

The only consensus of opinion on cathedral ceilings, aside from their beauty, is that they don't belong in a Canadian climate. The ideal Canadian cathedral ceiling would be two flat roofs leaning together at a steep angle and having enough space between the ceiling and the roof for insulation plus a crawl space.

Though I'm reluctant to make any recommendations on ventilating a cathedral ceiling, or what is often called a "compact roof", here's the best information I've been able to find:

If you insist on exposing the roof from underneath and then insulating it, you will have to carefully develop your own compromises. Insulate with Styrofoam on the outside and no ventilation is required at all. But that's very expensive, especially if you don't need to change the shingles anyway.

From the very small data available it appears that insulation placed on the inside should have a vent space behind it in warmer regions of Canada, but none in colder regions. (search keyword "attic" for the title " MYTH: THE MORE ATTIC VENTILATION IN WINTER THE BETTER." for some understanding of sealing the attic vent space.) If there is to be a vent space, it requires a cold outdoor-air input on the bottom (continuous soffit vents) and an exhaust for every section on the top (continuous ridge vents). If you are blowing loose fill into a ceiling joist cavity, fill it all up and close off the ventilation, as anything less is impractical.

Seal the ceiling as best you can. (search keyword "sealing" for the title "WHERE SHOULD I SEAL AND HOW?") Varnish on exposed beams will help, but fill the beautiful cracks first or they will allow moisture to bypass the varnish. Caulk between the beams and the interior paneling, and hide the caulking with wood trim. Reduce the moisture level as much as possible in the house. (For more negative information, search keyword "roof" for the title "ROOF INSULATION")

Keywords: Cathedral Ceiling, Roof, Ventilation

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