Foam against moist walls

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  #1  
Old 03-21-10, 05:25 PM
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Foam against moist walls

How big a problem is it to attach XPS or EPS directly to moist basement wall? The basement will remain unfinished. Will these materials create mold or other issues? Everything I see emphasizes problems with bats and studs for finished basements. Savings would be large - calculated at $450 per year for 1100 sf basement.

My thought is to only attach the material halfway down the wall, which would allow any moisture to drain and would avoid the most moist areas. I would attach with vertical lines of adhesive, and then blow foam to seal against the sill beam.
 
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  #2  
Old 03-22-10, 07:30 AM
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What's the cause of the moisture? I think your time and money would better be spent fixing your moisture problem. 2" foam boards are pretty expensive ($25 a sheet) EPS without foam backing are cheap though (I think like $10 a sheet or something). I used 1" inch EPS (with foil backing) on my basement, very cold day you can still feel a little bit of coldness on the surface (unscientific hand test).
 
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Old 03-22-10, 07:52 AM
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Hi Buffalo, I know it is obvious, but I have to say, first do all you can to eliminate the moisture. Now, the purpose of using rigid foam is that it does allow moisture to travel through it, all-be-it very slowly. But that would only be able to handle the normal moisture that diffuses through a concrete wall, not water but vapor. Limiting the foam to the exposed foundation, plus one foot below grade will take care of the majority of the heat loss and minimize the exposrue to the water leaking in. Remember, evaporating water takes about 1,000 times as much energy as raising it one degree.

As for mold, it needs three elements, spores, moisture and something to feed on. Spores are everywhere, you know there is moisture, so your only possibility to avoid it is to avoid any food/organic material. Since the foam is not food, avoid any wood products or sheetrock. It is a risky process, covering a wall that you already know is wet, but you are there to judge it better than others.

Now, for that calculated savings, optimistic. If you are living in a house above that basement, then basement walls only represent maybe 20% of the total heating costs. Insulating the wall area proposed might reduce that to 10%, which would imply your total heating costs are currently in the $5,000 per year range. I assume they are not that bad and we can go over the potential savings if you would like.

Bud
 
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Old 03-22-10, 09:07 AM
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Thanks for this input - this is very helpful. Very hard for me to address moisture, and I think that it mostly has been addressed by fixed gutters. To install drain tile would mean tearing up my neighbors concrete driveway (welcome to the city..).

Nate: did you see the effect in your heating bill? Are your 1st floor floors warmer?


Bud:

Originally Posted by Bud9051 View Post
Now, for that calculated savings, optimistic. If you are living in a house above that basement, then basement walls only represent maybe 20% of the total heating costs. Insulating the wall area proposed might reduce that to 10%, which would imply your total heating costs are currently in the $5,000 per year range. I assume they are not that bad and we can go over the potential savings if you would like.
Bud
Because my house is old style, the concrete block extends 3.5' above grade. For calculation purposes, I estimate that the wall is at design temperature to 2' below grade - so 5.5' of R-1.1 block wall, with 160' perimeter of wall. Even at 55F, the energy loss is pretty huge, and I came up with about 40% of my design loss once I insulate the upstairs walls this summer. I was really surprised.
 
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Old 03-22-10, 10:02 AM
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Yes, that is a lot of exposed concrete and as you know, concrete is BAD when it comes to heat loss. I'm assuming that you don't run a thermostat down there, so the inside temp actually tracks to some degree the outside. That effectively lowers the delta T a bit.

My son built a new home with 4' exposed basement walls and they light up with the IR camera. He is in the process of covering them and he keeps very good records for fuel use, so I should have some real numbers in a year or so as to the benefit.

But no question at all that it will save and I also like the simple math applied to a specific area, it is a real good way to judge potential savings. What the big software packages do that we can't with just the heat loss equation is account for solar gains and thermal mass. Plus the soil itself adds stability to the outside surface temperature. That is why I use just one foot below grade as I feel below that the yearly temperature difference is much less.

Just so I'm advising you properly, some jurisdictions will require a fire barrier over that rigid foam. 1/2" of paperless sheetrock is most common, although there are some expensive fire rated paints coming out.

If you haven't read about air sealing as yet, I'll attach a link just in case. It is a bit slow to open, but a good reference.
http://www.efficiencyvermont.com/ste...ide_062507.pdf

Bud
 
  #6  
Old 03-23-10, 06:46 PM
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Adding sheetrock will complicate this, but is a good idea. My plan is to only insulate the upper half of the wall, and leave the slightly damp (and warmer) lower area exposed. SO, I would glue and foam the beadboard to the concrete blocks.

If I attach sheetrock, the weight won't allow me to just use glue. Especially as the block is 1920's textured block, and it will be hard to get a solid adhesion. I'm hesitant to shoot nails or screws into my old block.

SO... maybe use widely spaced studs, even just 2x3's from the floor up to give a vertical support to the sheetrock. Then between the studs and the glue, everything would hold up? Or, maybe it would be OK to just screw into the old concrete blocks? That would be a lot easier.
 
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Old 03-25-10, 12:57 PM
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hopefully not thread-jacking, but I noticed the original poster in the first post made a comment about saving money. Was this to say that xxx amount of money is lost when heat travels through the uninsulated studs? Is it that much of a difference?
 
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Old 03-27-10, 07:14 AM
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mjjstang: for my 1100 SF basement, I calculate that I spend $475 per year heating energy that is lost through the basement walls alone. This is based 55F interior temp, 6F exterior temp, 6500 HDD, 160' perimeter, 5.5' height of block exposed (3.5' above grade and 2' below), R-1.1, and correction factor (Cd - from ASHREA) of 0.62. All of this is following the method from "Modern Hydronic Heating", 2nd ed, Siegenthaler.

Bringing that wall up to R-7 saves me about $325 per year based on my calcs. Pretty big number. It would be nice to have a warmer first floor too.
 
  #9  
Old 03-27-10, 03:48 PM
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mjjstang: Buffalo's calculations are using the average wall value which would include the reduction for studs when present. But studs do make a difference as the R-value for them is in the R-1.25 per inch range. So a 3.5" stud is just over R-4. When that is averaged in with the insulation, it does cost some, but only in the 5% to 10% range (just a rough guess).

Bud
 
  #10  
Old 04-08-10, 06:29 AM
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I finished my basement a couple years ago. I have poured concrete walls in my basement. I painted all my walls with dry-lock purchased from home depot then added glued foam insulation slabs to the walls then put up 2/4 studs. If it rains a lot outside I can feel a little humidity in my basement but not much. Other then that it is cool and dry at all times.
 
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