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Community and Q&A

Mold appearing in a recently spray foam insulated room

NBSRWeGF9D | Posted in General Questions on

Approxiamately 1 year ago, I was involved in a home basement renovation that included spray foaming the headers throughout the basement as well as insulating all the exterior walls(2 out of the 4 were exterior) of a converted storage/cold room(appr. 5’x 12′. In the last month or so, the home owner discovered mold along the entire length of the baseboard and part of the way up the wall, on the longest of the 2 foamed exterior walls, approx. 12′. The ext. walls have about 4-4.5″ of closed cell insulation and there was also a heat vent installed, dropped to just above floor level. The ceiling is not that of a typical cold room where the porch is above rather it is the floor of one of the interior rooms on the main floor, so I can’t see how this room is any different than the rest of the basement. The other baffling thing is that the door is left open all the time and there has been an oscilating de-humidifier running just outside the room(to my understanding it runs all the time). There is also a new window installed in the room that is energy star rated so the room is pretty air tight and not in darkness all the time. I am looking for any ideas on why mold would be appearing. My only guess is that the floor, which is tile on concrete, is a source of cold for condensation to happen. I’ve worked in many basements however and have never seen this to be an issue. I would like to be the hero here and offer my client an answer and a solution.

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  1. GBA Editor
    Martin Holladay | | #1

    You don't quite give use enough details to visualize what you are talking about. But if there is mold, there is moisture. To figure out what's going on, you need to find the source of the moisture.

    You say there is moisture on "an exterior wall." You also call this a basement. Is it a below-grade wall or an above-grade wall? If it is below grade, please describe all the layers. Is it poured concrete + spray foam + studs + gypsum wallboard? Or something else?

    Near the end of your paragraph, you say that there might be condensation on the floor. Is the floor insulated with foam or not? Do the homeowners leave any windows open to allow exterior air to enter the basement?

    Of course, many basements are damp because the exterior grade slopes toward the foundation, or because footing drains are missing or clogged, or because the site has a high water table. All possibilities need to be investigated.

  2. NBSRWeGF9D | | #2

    Your right Martin....moisture source. Upon further investigation, it turns out the moisture source is most likely from the main water line coming into the house in that room. The majority of the pipe is insulated save the bottom 6" or so and the meter itself. We're thinking that the combination of the uninsulated portion of the pipe sweating and the fact that several boxes may have been positioned to closely to the problem wall is what has provided the moisture condition that started the mold. We will address the pipe and keep an eye on it for a while.

    For the meter, is wrapping in some batt insulation sufficient?

  3. GBA Editor
    Martin Holladay | | #3

    Because fiberglass insulation is air-permeable and vapor-permeable, it's not the best choice for this application. The best thing to do would be to build a little box out of rigid foam, held together at the edges with housewrap tape. It should be designed in such a way that it can be lifted off when necessary to read the meter.

    Also -- it wouldn't hurt to buy another dehumidifier and put it in the room with the problem.

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