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Community and Q&A

What is the best scissor truss venting/ insulating option?

Joseph Isherwood | Posted in General Questions on

I am using 12″ raised heel scissor trusses for a cathedral bedroom. One end wall, other connecting to 8 pitch raised heel truss. With valley connecting trusses and main truss no soffit venting area available. What insulation and venting would be best?

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Replies

  1. User avatar GBA Editor
    Martin Holladay | | #1

    Joseph,
    Roofs with valleys can't be vented, so you are restricted to unvented options.

    There are two basic approaches. Either:

    (a) Install an adequately thick layer of rigid foam above the roof sheathing, with or without supplemental fluffy insulation under the roof sheathing (and in direct contact with the roof sheathing), or

    (b) Install an adequately thick layer of closed-cell spray foam against the underside of the roof sheathing, with or without supplemental fluffy insulation under the cured spray foam (and in direct contact with the cured spray foam).

    Both options are fully explained in this article: How to Build an Insulated Cathedral Ceiling.

    You asked, "What would be best?" The answer to that question is to install rigid foam above the roof sheathing.

  2. Joseph Isherwood | | #2

    Thanks Martin, Would u advise with option B given they are 5 pitch scissor trusses to only spray foam up to the point of having space between upper and lower chords. Also, if using foam can I still use 3/4 polyiso between furring strips on bottom ? How about a gable vent to go with the ridge vent?

  3. User avatar GBA Editor
    Martin Holladay | | #3

    Joseph,
    Your questions are confusing. Time to post a sketch of what you have in mind, showing how the various roof slopes and trusses meet.

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