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strategery 07-20-2011 02:00 PM

Want to insulate walls in my unfinished basement
I have an unfinished basement with the old clay red block foundation. I want to insulate the basement walls to help make the floors warmer upstairs. I already had the band joists spray-foamed.

I wanted to do this myself by purchasing some foam boards at a big box store and taping them at the seams.

My concern is about the moisture. My damp basement would be in the upper 70s or 80s in humidity % if I weren't running my dehumidifier constantly. If I put up these foam insulation boards, won't it trap moisture behind them and cause the foundation walls to rot and weaken?

Please help! Thanks.

Gary in WA 07-23-2011 10:38 PM

The foam boards are the best way to go. Problem is they need to stop any basement air from reaching the cold brick wall;

Moisture per location:


strategery 07-24-2011 02:02 PM

Thanks for the reply.

Your first link didn't work for me. Does it say that I should prevent air infiltration before the insulation? What kind of material do I put on the concrete foundation before the insulation?


P.S. I need to have this project COMPLETED before winter. My wood floors can get pretty cold and I'm trying to change that.

Gary in WA 07-28-2011 10:51 PM

Yes, the concrete should not get any basement air to it; The foam board releases the moisture slowly. Irregular walls are a challenge:


strategery 08-17-2011 03:43 PM

Can I ask another question and hopefully it's not a stupid one?

So I'm going to glue 2" of foam board XPS insulation directly to the clay block foundation wall. What kind of air sealing film or wrap should I be looking for to put over top of the insulation?

AGWhitehouse 08-17-2011 04:04 PM

You might want to check with your local building department as most codes are now requiring that foam insulatioin be covered with a ignition and thermal barrier. If this code exists in your area this would mean that you would have to cover the foam with some form of sheetrock or equivalent material to protect the foam adding an expense to the project.

If living floor warmth is your #1 goal, you may want to consider just insulating your floor joists. It would be cheaper and more efficient in the long run. Insulating just the basement walls would only solve a part of the basement heat loss as a relatively equal amount of heat is lost through the floor slab.

Gary in WA 08-17-2011 07:04 PM

"What kind of air sealing film or wrap should I be looking for to put over top of the insulation?"-------- no covering on the foam board. Tape the joints against air movement, canned foam the bottoms to the concrete.

Where are you located?

Describe the finished wall.....


strategery 08-18-2011 08:14 AM

Located in Iowa.

I don't intend to finish the basement at this time, so no wall will be put up after the insulation. I'm just using it for storage, my hvac system, water heater, and washer & dryer.

Just want to add the insulation for comfort. There's a rebate from the energy company for doing this.

AGWhitehouse 08-18-2011 11:36 AM


Originally Posted by strategery (Post 709865)
I don't intend to finish the basement at this time, so no wall will be put up after the insulation.

If you're going rigid foam insul, this would be against code in my region. Best to check with your local Building Department.

Gary in WA 08-20-2011 01:35 PM

R-10 continuous insulation is required for your location in basements. As AGW said, cover the foam board unless it is fire-rated:

Any foil-faced foam board is not recommended above grade on the basement walls to permit drying.


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