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Community and Q&A

Cellulose insulation in new saltbox roof (Zone 5a coastal)

John Rockwell | Posted in Green Building Techniques on

In order to minimize Treated Floor Area, and to simply enclose a proposed house with less volume on the second floor, I plan to use a saltbox roof. Are there any concerns with transitioning from dense pack in the unvented slopes to loose fill above the flat ceilings? Or should there be a vent channel in the slopes only that rides up higher than the depth of the loose fill?

Also, I am not planning to use a ridge beam, so collar ties of some sort will be needed for a stick-framed roof. If their ends penetrate into the roof member cavity, I am concerned about continuity of the thermal barrier. Perhaps a simple truss will keep the bottom member outside the insulation cavity, then use I-joists (to maximize depth) for the sloped ceilings?

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  1. GBA Editor
    Martin Holladay | | #1

    Q. "Are there any concerns with transitioning from dense pack in the unvented slopes to loose fill above the flat ceilings?"

    A. Yes. It is a code violation to install dense-packed cellulose in an unvented sloped roof assembly. For more information, see How to Build an Insulated Cathedral Ceiling.

  2. John Rockwell | | #2

    It was hard to keep that question concise. I'm primarily concerned with the junction of sloped ceiling with flat and the optimal insulation technique with a possible change in structure.

  3. GBA Editor
    Martin Holladay | | #3

    Extend your baffles (the sheet goods used to maintain the ventilation gap) well beyond the level of the top of your attic insulation. Your baffles should be installed in an airtight manner to maintain an air barrier above the cellulose in the rafter bays.

    When it's time to blow insulation on your attic floor, pile it on deep.

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