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Community and Q&A

Contractor for rigid insulation roof system in Chicago

lincolnpark | Posted in GBA Pro Help on

I have a vaulted ceiling on the 3rd floor of my home in Chicago and we have interior condensation condensation issues during the winter.  I’m currently inclined to replace the current roof with a rigid insulation system installed above the roof deck.  I’d like it to at least meet the minimum required R-value for continuous insulation.

It’s been a challenge to identify an appropriate contractor for the job. The ones I have spoken to only do flat roofs or aren’t familiar with the concept. Any suggestions would be much appreciated. To the extent it helps, please see the attached photos.

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  1. Expert Member
    Akos | | #1

    Exterior roofing insulation retrofit is not very common. A couple of times I've had it quoted, it came out significantly more than spray foam costs, which is silly as the materials are not that much and the labour is similar to a re-roof.

    That one area I've had luck with is people that do flat roofs as it is common for them to install rigid insulation under torchdown. The cost delta there to add a couple of inches of rigid insulation was pretty minimal.

    Since your roof is pretty simple and the shingles are in decent shape, about the only questionable detail is the lack of soffit vents. It might be simpler to add in the the proper venting details and do a good job of air sealing the interior ceiling.

    Something like this:

    For air sealing, make sure to remove ALL pot light cans (some of these can be replaced with the new slim LED ones that as these are much better sealed) and be meticulous around your skylight. These are the usual culprits for ceiling condensation.

  2. lincolnpark | | #2

    Thank you. The soffit is vented and there's a ridge vent. However, the 6" of space between the ceiling and roof is packed with 8.25" kraft-backed fiberglass. It appears that some baffles were installed but the one I inspected (removed a pot light and as much insulation as I could) is compressed and doesn't extend up the roof very far.

    We have 17 pot lights in the ceiling and they are absolutely not helping! Given the compression of the insulation, I'm assuming I'm getting no better than R-24 (given the space taken up by the pot lights, it's much less).

    I have no doubt that removing the pot lights, etc. would improve the condensation issue significantly. Best case, I'd eliminate the condensation but I'd still have an under-insulated roof that may not be be sufficiently ventilated (how would I tell?).

  3. Expert Member
    Akos | | #3

    I'm not sure if I understand your celing correctly, but if you rafters are 2x6 the best you would get with the 8" batts compressed is around R22 assuming no space for vent baffle. So that is an R19 whole roof assembly. If the rafters are 2x8 with the same batt you are closer to an R23 roof, bit better but not by much.

    In Chicago with an outdoor temperature around 0F, you would loose 4000btu per 1000sqft of roof. If you bump it up to code with is R38 whole roof assembly, that number drops to a bit under 2000btu. Better but not by a lot.

    You can probably get similar energy savings for much less by air sealing the house. Getting rid of those pot lights should definitely be the first step.

    The over-insulation would only really be worth it if you need to replace the roof, even then the cost of the insulation would have a very long ROI in energy savings.

    I light my entire place without any pot lights using a combination of indirect and accent lighting. Many people have commented on the quality of the lighting in the place as it is much more pleasant without the glare or shadows of ceilings shotgunned with pot lights.

    About the only good thing about pot lights is that they are cheap. The light they provide is not very pleasant, cause endless issues in cathedral ceilings as you have found out.

  4. lincolnpark | | #4

    Thank you. Your analysis makes a lot of sense.

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