Gap or Seal Between Vents in Cathedral Ceiling
I am confused if proVents should have a 1″ gap between proVent pieces in a cathedral ceiling or not. Both Holladay and Lstiburek say that the vent channel in a cathedral ceiling should be airtight:
* https://www.greenbuildingadvisor.com/article/how-to-build-an-insulated-cathedral-ceiling and
* https://www.finehomebuilding.com/2011/07/14/a-crash-course-in-roof-venting
Lstiburek even says that Accuvent, a similar product, should be sealed with spray foam at the joints.
However, the manufacturer of proVent says “keep a one inch space between vents in cathedral and finished attics” (http://adoproducts.com/as_proVent). This position is repeated several times on the Home Depot Q&A: https://www.homedepot.com/p/ADO-Products-Provent-14-in-x-4-ft-Rafter-Vent-UPV14480/100533902 In both cases the justification is moisture handling.
Since the advice is opposite, I’ve concluded it doesn’t really matter. What am I missing?
FYI, I live in central Texas, zone 2A.
Mark
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Replies
Hi Mark,
It is possible the confusion lies with the fact that, according to research done by Martin Holladay, "When guidelines for attic ventilation were first proposed in 1942, no one anticipated that these guidelines would eventually be applied to cathedral ceilings. Rose and TenWolde note that vent channels above cathedral ceiling insulation aren’t very effective. The authors wrote, 'Venting rules for attics have been extended to apply to cathedral ceilings, but few studies have been made to confirm the validity of that extension.'” There are a number of links to resources you might find helpful in this article, which looks at the question What about cathedral ceilings?
Generally, air sealing on both sides of a wall or ceiling is beneficial. If you can only do one side, then the exterior is more important with AC and the interior is more important when heating.