Question:

Hello Mr. Wiseman, I don't know if you can help, but here is my question. I live in an approx 5 year old house and we have a small deck with a patio door leading off our kitchen. All around our patio door and on the siding (outside, not indoors), is what looks like black mold forming in very small dot like fashion. What the heck can be causing this, and is there something I can do? Thanks for your time. Kerry LeBlond

Answer:

The times when I have seen this type of thing have been in a situation where the house has been under positive pressure. What happens is the more humid indoor air is forced into the colder exterior cavity of the home and ultimately to the outside where you see evidence on siding etc. Because there is this cooling, the air will reach the dew point and condensation will form, leading to the other detrimental effects thereof. The solution is to identify why the home may be under positive pressure and remedy this forthwith. The most common cause is an improperly installed or operated air exchanger. The problem will be exacerbated if there is a lack of return air to the furnace. Please feel free to contact me if you would like to discuss this in more detail. Best Regards, Glenn Wiseman, RASDT, RHDT

Answered By: Glenn Wiseman

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