Rigid foam board on recessed wall

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Old 06-02-10, 12:06 PM
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Rigid foam board on recessed wall

I'm not exactly sure what this type of basement wall is called. I have a cinder block wall that thicker on the bottom half then the top half. You can see it in the picture. Does anyone know the name of this type of wall? I'd like to install rigid foam as insulation but all the instructions assume a flat wall. How can I do this on this type of wall? Also how would I go about installing the foam around the water pipe or gas meter as pictured?



 
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Old 06-02-10, 01:41 PM
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Hi vman and welcome to the forum. I will assume from your handl you are in NJ, so some frost and some cold. Can't say why they built that out, could have been done when constructed or added later. Depending upon what you are looking to do, you can add a couple of inches of rigid to the upper area, some on the slope, and then one inch below. Omitting the areas where water and gas pipes are. If that is a 4" step and you added 2" up top and 1" below, you now have a 3" step. Use 2x6's and remove 3" in width on the lower half, match the wall, and frame away. Pressure treated on the bottom and a 2x6 top plate. Before the wall goes up, carefully air seal and insulate the rim joist all the way around. Check with your termite inspectors to see what they might need for access for future inspections.

As for covering the water and gas, I wouldn't, at least with anything permanent. You should have access and you don't want to isolate them from their heat source, the room.

That should get you started. Others will add their thoughts.

Bud
 
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Old 06-03-10, 11:57 AM
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Thanks for the welcome and info bud. I never thought to alter a 2x6 to fit the wall. I believe it was originally built this way, not sure why. It makes everything a pain in the ass.

So you suggest I cut the rigid foam in 3 sections, fasten them to the wall, then tuck tape them together? I'm curious though, why only an inch below the angle in the wall? What if the angled part was below grade? Would you still suggest this?
 
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Old 06-03-10, 07:53 PM
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Below grade requires much less for insulation. My normal recommendation is to insulate the above grade exposed concrete plus one foot below grade, all insulation on the inside. Below that one foot line, the resistance of the soil slows the loss of heat, which is what insulation does. The farther below grade, the less insulation you need. Concrete walls also need to breathe a little. Since there is always moisture on the outside, moisture in the blocks themselves needs a way to get out. Right now it is evaporating to the inside before you see or feel it, but it is there. One inch or rigid foan, no plastic or foil covering, will allow a slow diffusion of that moisture so the moisture level in the blocks doesn't build up to match the outside conditions.

The upper portion of the walls, especially any exposed surfaces, is the most important.

Bud
 
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