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Community and Q&A

Unvented cathedral ceiling?

John Roy | Posted in Energy Efficiency and Durability on

Having just read Martin’s interview with Bill Hulstrunk (technical manager at National Fiber) I am completely and utterly confused when it comes to whether to vent or not in a cathedral ceiling. Is there a definitive answer to this??? Would not one better served by providing an air space (as cheap insurance) to make sure water vapor doesn’t migrate either from the outside or the inside?

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Replies

  1. GBA Editor
    Martin Holladay | | #1

    John,
    Here at GBA, I have been consistently advising people to include ventilation when using cellulose to insulate a cathedral ceiling.

    Bill Hulstrunk's company, National Fiber, feels confident enough in their technique to provide a warranty that such installations will not cause problems. Other cellulose manufacturers (notably U.S. GreenFiber of Charolotte, NC) disagree with Hulstrunk, and advise customers to include ventilation between the insulation and the roof sheathing.

    The debate may be moot in most jurisdictions, however, since most building officials interpret the code more narrowly than Hulstrunk, and insist on ventilation.

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