GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Plus Icon Minus Icon Picture icon Hamburger Icon Close Icon Sorted

Community and Q&A

Condensation issue with roof

Brad964C4 | Posted in General Questions on

Just got a call from a builder who recently completed a house I designed her in Ct. (zone 5). He didn’t install soffit vents or ridge vents since he was supposed to use open cell spray foam in the rafter cavities. Turns out he didn’t foam the rafters, but use fiberglass batts (with baffles) instead & is now seeing condensation dripping from the rafter tails & down the soffits.Air handlers & ducts are in the attic, so I’d prefer to keep the insulation in the rafters.

Potential solutions include:
1. Remove the batts & install spray foam in the rafters.Best solution in my opinion, but probably won’t happen due to cost & messiness as the house is now being lived in.
2. Install soffit vents & ridge vents.
3. Install soffit vents & a power vent. This is the roofer’s suggestion, but I think this would only remove air from the attic & would not work the same as a ridge vent.

Any comments on these solutions (or others) would be appreciated!


GBA Prime

Join the leading community of building science experts

Become a GBA Prime member and get instant access to the latest developments in green building, research, and reports from the field.


  1. GBA Editor
    Martin Holladay | | #1

    I certainly hope that the homeowner ends up with a code-compliant roof, regardless of the cost, in light of the builder's error.

    A code-compliant roof needs to meet minimum R-value requirements, which are probably R-49 in Zone 5 (but which may be less if local codes haven't been updated recently).

    The power vent is a very bad idea. In addition to wasting electricity, it will drastically reduce the thermal performance of the fibrous insulation -- from R-24 (just guessing) to something closer to R-1 (again, just guessing).

    Here is a link to an article that explains all of your options: How to Build an Insulated Cathedral Ceiling.

  2. Expert Member
    Dana Dorsett | | #2

    +1 on power venting being the anti-solution.

    How deep are the rafters?

    How complicated are the roof lines? (any valleys, hips or dormers?)

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |