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Community and Q&A

Re-roofing and insulation sequence

DCLittleHouse | Posted in General Questions on

If we are going to re-roof the house and add the blown-in insulation (currently, none), should we do that before the shingles or after?  or, it doesn’t matter?

The house is in CA.  I asked because I thought they would do that after the old shingles were removed and before the new shingles were installed.  I called the office and the project coordinator told me that I didn’t order the insulation.  I called the sales rep and he told me that it didn’t matter and the roofer would install the shingles and insulation would be blown later.   However, when the insulation company called and asked to gain access from the house so that they could blow the insulation to the attic, I told her that there were no access.  I told her that if they needed to punch a hole or use the vent to access the attic, they must put everything back in good condition.  Then, I don’t know why the roof company didn’t put the new shingles.  After the insulation was blown, the roof company said it was ME who requested to have the insulation first and their crews were busy working in other sites.

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  1. Jon_R | | #1

    I would post your entire insulation result and climate zone.

  2. seabornman | | #2

    Some re-roofing projects can expose the structure below to dirt, debris, nails, and water. Not knowing the details of your project, in general I'd say insulate after.

  3. Expert Member
    Dana Dorsett | | #3

    I'm inferring from the name that this is in Washington DC, (US climate zone 4A), and that the insulation is open-blown fiber on the attic floor.

    If that is what you're doing the order doesn't really matter, unless the roof is leaking so badly that it would wet the insulation.

    If insulating at the roof deck level there are some issues to sort out.

    For open blown fiber on the attic floor what does matter is to FIRST meticulously air seal the attic floor at all electrical/plumbing/flue penetrations before blowing in insulation.

    IRC code min is R49, which requires 13-14" of depth if using loose cellulose or mid-density fiberglass, which might not be possible to achieve all the way out over the top plates of the exterior walls.

  4. GBA Editor
    Martin Holladay | | #4

    If you are talking about a cathedral ceiling or a conditioned attic where the insulation follows the roof slope, the sequence definitely matters -- because there may be a good reason to install exterior rigid foam before you install new roofing.

    For more information on this topic, see "Plan Ahead for Insulation."

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