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Community and Q&A

Roof insulation choices

Joe Norm | Posted in General Questions on

Hi There,

I am using open web trusses for my shed roofed new construction home. Probably a little overkill but oh well.

My plan was to go with blown-in cellulose but recently I have been tempted by self installed batts because of the money I could save.

My lower story will have a 24 inch deep truss and my small upper story will be 18 inch. Both roofs will be vented.

With cellulose i would have to ensure there was a robust air gap baffle that would not get “pinched off” in the installation. With batts I’m wondering if I can just push them up, knowing that a vent channel will be left.

At 24 inches, I could put two layers of r-30 batts and still have ~8inches of air gap. I would have closer to 2 inches with the 18’s

Downside to batts is that I leave “gaps” at the interior of the webs of the trusses. Cellulose would likely fill these gaps a little better.

Also wondering about the gable ends. Outlookers will be on edge, so the last two trusses are lowered so the 2×4 can run over the top of them. This creates an interesting zone to insulate, as there is less of a free running air space from eave to eave. Any thoughts on this area?

thanks for the input.

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  1. GBA Editor
    Martin Holladay | | #1

    To limit windwashing, you want ventilation baffles between the insulation and the air channel above. Ideally, these ventilation baffles will be installed in an airtight manner. For more information, see "How to Build an Insulated Cathedral Ceiling."

  2. Joe Norm | | #2

    Thanks Martin, can you recommend a material for the baffles?

    1. GBA Editor
      Martin Holladay | | #3

      If you read the article I linked to -- "How to Build an Insulated Cathedral Ceiling" -- you'll find a discussion of baffle materials and recommendations.

      For an extended discussion of the issue, see "Site-Built Ventilation Baffles for Roofs."

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