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Condensation on uninsulated ceiling

aekatz | Posted in GBA Pro Help on

I have a ceiling above my root cellar which is below ground, attached to my basement via an external grade steel door, outside my homes thermal envelope, and passively ventilated with intake exhaust piping. The walls are ICF (as is the rest of the house), the floor is patio pavers/gravel over soil, and the ceiling is a galvanized steel-type pan with reinforced concrete above (forming the floor of the porch, above, I get condensation forming on the metal ribs of the ceiling and need to control it as I need to install electrical fixtures and found about about the condensation after water infiltration shorted out one of these. Will spray foam or rigid foam insulation alleviate the problem? If so, do I want closed cell or open cell foam?

The goal in this room is cool temperatures and elevated humidity for storage of root vegetables and wine, so active dehumidification is not acceptable. Furthermore, the house itself is up for LEED certification so I don’t want to violate my goals there. We have an air intake PVC pipe running about 5-6′ below grade entering the room at a low level to let in cool air and a similar pipe at ceiling level to let out warm air. There are manual gates to regulate intake/exhaust.

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  1. GBA Editor
    Martin Holladay | | #1

    The best product to use would be closed-cell spray foam, although rigid foam (carefully installed) would also work.

    On the interior side of the insulation, you'll want to install a durable covering for fire safety and protection. Either moisture-resistant drywall or cement-board underlayment are possible sheet materials for your ceiling. Before doing the work, confirm your ceiling choice with your local code enforcement authority.

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