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I have a half vault ceiling with 3 vertical skylights at the peaks

Bmcmil2 | Posted in General Questions on

I have a half vault ceiling with 3 vertical skylights at the peaks. It was condensating a lot so we had the blown insulation stuffed between, in between the ceiling joists, from the soffit. There is no ridge vent as it’s cut off at the windows. Even after replacing…

The skylights windows are single-pane and the rising sun hits them quickly. The ceiling surface reads 100 degrees at this during the day.


  1. user-2310254 | | #1

    Cellulose in an unvented cathedral ceiling is not a good idea. Where are located? And be sure to read this article:

  2. Bmcmil2 | | #2

    I see code for unvented attic assemblies is to have a rigid foam board after the roof sheathing. I had insulation work done less than a year ago and they did not do that. It did not have the foam boad before. Technically the attic space is vented as there is a soffit vents. Do I have a case that it wasn't done to code with the updates?

  3. Bmcmil2 | | #3

    I'm located in southern Louisiana

  4. GBA Editor
    Martin Holladay | | #4

    There are lots of issues here.


    1. Your roof assembly needs to be airtight. If you aren't sure whether your roof is tight or leaky, you need to verify the tightness of the roof assembly with a blower-door test or a theatrical fog machine test. If you aren't sure how to perform these tests, use the GBA search box to learn more. If testing shows that your roof assembly is leaky, you need to come up with a plan to seal the leaks.

    2. Your roof assembly needs to be well insulated, in a way that complies with the building code and in a way that conforms to building science recommendations. This article provides advice: How to Build an Insulated Cathedral Ceiling.

    3. Your single-glazed skylights probably need to be replaced with new, double-glazed skylights.

  5. GBA Editor
    Martin Holladay | | #5

    If your insulation contractor included a vent space between the top of the insulation and the underside of the roof sheathing (by installing ventilation baffles in the rafter bays before the insulation was installed), then the job probably complied with building code requirements.

    If your insulation contractor installed "blown in insulation" -- that usually means either cellulose or blown-in fiberglass, but in your case I'm not sure what it means -- without first installing ventilation baffles, then your insulation contractor created a roof in a way that violates the building code (unless the contractor installed spray foam -- but most people don't call spray foam "blown in insulation").

    The final wrinkle is this one: renovation work is usually exempt from any requirement to follow building codes. If you want to know more about local code requirements, call up your local building department.

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