insulated basement with spray foam...problem??

werewithallOctober 11, 2011


My house is 80 years old.

In my effort to make our house more energy efficient, I had the basement insulated 3 years ago.

I decided to use the spray foam type of insulation and hired a local insulation company to do the work.

They sprayed all 4 walls of the basement from the ground up to the ceiling.

In terms of efficiency, I am very happy with the results - the floors on main level are warmer & our utility bills have gone down.


I have noticed that our house smells a little musty & not fresh. I especially notice the smell in the spring and fall when the AC & furnace aren't running. I also notice the smell on our carpeted stairs and on our microfiber couch (mostly hardwood floors & leather furniture otherwise).

I'm worried that the spray foam insulation has made the basement too airtight and the house cannot "breathe". Could this be the cause of the musty/stale/damp smell?

How can I fix this?

Any suggestions will be very appreciated.

Thanks & regards.

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Your home is sick. While I am not sure of the underlying cause, you should start treating the symptoms while you are figuring it out. If you don't, you will continue doing, possibly irreparable, damage. Get a couple of inexpensive electronic hygrometers. (While they both agree, they are probably accurate.) Get a dehumidifier. Run the crap out of it if you need to in order to keep the relative humidity between 30 and 50%,

Where are you located and what is the climate like? Is this open-cell or closed-cell foam? Is this basement all underground or are some or all of the walls exposed. What are the basement walls and floor made of? What kind of AC do you have, central?

    Bookmark   October 11, 2011 at 2:59PM
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Thanks for responding Ionized.

I live in the Detroit area.
Insulation is closed-cell foam.
The entire basement is underground (no exposed walls).
Basement walls are cement block and the floor is cement.
We have central air.

I started running the dehumidifier a couple of days ago, which seems to help out.

Thanks again.

    Bookmark   October 11, 2011 at 3:17PM
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Good. Right now I don't have any real good ideas about why the humidity would have increased dramatically beyond the fact that you will might not be running the heat and cooling so much. Both of those factors would lead to increased humidity.

The fact is, I don't think that insulating the basement walls would have led to that much of an improvement in heat transfer. Usually the ground temp is moderate enough that insulating underground walls is not the first thing on the list to energy efficiency. Note that insulating exposed wall just above the foundation is often overlooked.

How long did you live there before you did the spray foam? What was the humidity level running before you added the dehumidifier? I hope others might have some additional ideas.

    Bookmark   October 11, 2011 at 7:38PM
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Foaming basement walls is a good idea. Humidity must be controlled regardless.

    Bookmark   October 12, 2011 at 5:17PM
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The foam is great as a thermal and vapor barrier for the walls. But the mositure that comes from the ground through the the basement cement floor has no place to go. The DH will solve this problem. I had a similar issue with a brand new house and cellulose insulation. During high humidity or after a lot of rain we would get a musty smell and wet spots on the concrete floor. I put in a whole house DH and that sovled the problem. I also added a higher end tstat that has a humidistat inside. During the summer, the AC will run up to 3 degrees below the set point when there is high humidity detected.

Depending on how tight your house is - you may also need a source of fresh air. Check into an HRV or ERV.

    Bookmark   October 14, 2011 at 2:07PM
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