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Open cell cathedral ceiling/roof

Doug Godfrey | Posted in Green Building Techniques on

We just completed a major renovation of a house in CT that involved adding living space in the attic. The cathedral ceilings with dormers all have 8″ (approximate average in 2×10 rafters) open cell foam. Underside of rafters are drywalled and taped without paint and T&G wood bead board painted on both sides is installed for the finished ceiling. The problem is with the bead board expanding and buckling. From the construction photos I noticed that the 2x blocking to close off the rafter bays from the eaves were not installed. The post insulation photos show just big gobs of foam filling the void, but I can not tell you how completely it is sealed off. I am suspicious of this area.
It is summertime so there is lots of moister outside that wants to get in given the opportunity.
Anybody else had a similar issue?
Thanks.

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Replies

  1. GBA Editor
    Martin Holladay | | #1

    Michael,
    Open-cell foam is vapor permeable, so it's possible for exterior humidity to diffuse through the foam. However, it is not clear that such diffusion is responsible for your problem.

    1. What is the range of your indoor relative humidity? Have you been monitoring it?

    2. Is the home air conditioned?

  2. Doug Godfrey | | #2

    AC is on and apparently working within design parameters. So that I would assume the RH is constant on the interior.

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