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  #1  
Old 01/28/09, 06:21 PM
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Best way to insulate block basement walls.

I am thinking about insulating my basement walls for eventual finishing, I figure I might as well go ahead and do it. So far I have explored foam sheets (expensive) to go on top of the walls or filling the blocks with spray in foam, which is also expensive. Any thoughts or ideas?

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  #2  
Old 01/28/09, 08:17 PM
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Foam board insulation might be the best way to go, even if it is expensive. Filling in the cavities is just not economical; plus, you'll have gaps between the cavities that will leak cold. If the wall is already up, put one or two foam boards on the inside with construction glue against the wall. Seal all the joints with aluminum tape, then add furring strips over that (one-by-two dimensional lumber laid like studs over the insulation). Over that you can nail drywall.

In addition, cinder blocks are a very porous concrete (just pour water on one and it leaks through). Foam insulation might do the same, and something like cellulose would get wet and lose its efficiency.

I'm not an expert, but I found that info when looking into insulating old houses. In our basement the builders insulated with fiberglass R-11, and now it's dangling from the walls and tearing apart. It's so ugly.

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Old 01/28/09, 08:22 PM
 
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Yep, foam sheets.

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  #4  
Old 01/28/09, 08:53 PM
 
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Yes the spray foam is expensive, but it is the best. Besides insulating, it is also waterproof. Insects and mold hate it as well. It can be sprayed on any suface except plastic and the only thing that breaks it down are UV rays.

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  #5  
Old 01/28/09, 09:13 PM
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I have used a lot of spray-foam. It is good.

Your best would likely be hard foam sheets.

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  #6  
Old 01/28/09, 10:42 PM
 
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In one house with a severe basement water problem I put poly sheeting over the wall, studded it out, used R-11 batts, put another layer of poly on top of that LEAVING THE TOP 3 INCHES UNCOVERED, and put sheet rock over that. The open top allowed moisture to escape when the walls were warm, but sealed the insulation from the everyday moisture and condensation problems. After doing this, the basement was noticeably drier.

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  #7  
Old 01/28/09, 10:45 PM
 
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When I constructed my "water house" I used 2 inches of foam bead board on the inside and the outside of the 8 inch blocks.
Yes on the outside of the blocks . . . that in its self makes one heck of a difference.
"But I don't want to dig to do that"
Yes it would be labor intensive . . . but you would see a huge difference if you did.
Just putting insulation on the inside of those blocks can lead you to moisture problems down the line.

OK you asked...............

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  #8  
Old 01/28/09, 11:17 PM
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Quote:
Originally Posted by Jim-mi View Post
When I constructed my "water house" I used 2 inches of foam bead board on the inside and the outside of the 8 inch blocks.
Yes on the outside of the blocks . . . that in its self makes one heck of a difference.
"But I don't want to dig to do that"
Yes it would be labor intensive . . . but you would see a huge difference if you did.
Just putting insulation on the inside of those blocks can lead you to moisture problems down the line.

OK you asked...............
I was thinking the same, but didn't want to scare him too much. As far as moisture I'd think a typical parging/asphalt/french drain system would be adequate for several decades, but having insulation on both sides of the wall is definitely an advantage.
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  #9  
Old 01/29/09, 07:08 AM
 
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When I finished the basement at my mom's house, I used the 1.5"x 2 foot sheets of pink foam insulation, and installed them by putting 1x3 furring strips over the seams and then using tapcons to hold the furring strips up. The insulation was held up by the furring strips, not by adhesive. I did this because the blocks were painted and I didn't think glue would hold. I then drywalled over the furring strips using the moisture resistant green drywall and it turned out very nice. No moisture/mold problems so far.

Putting foam inside of the cement blocks would not give you much insulation, there would be a great deal of thermal bridging through the end/center webs of the blocks. I agree that insulation on the outside would be the most effective, but I'd only do that if you also had a water problem and wanted to install a new drainage system at the same time.

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  #10  
Old 01/29/09, 09:00 AM
 
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I will second the part about putting insulation on the outside of the block wall. It makes a significant difference even if its just 1" it provides a thermal break so the walls arent significantly cooler than the basement air. It fixes the condensation problems almost entirely by itself.

-Mallow

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