Finishing basement, insulation questions


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Old 07-20-09, 12:11 AM
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Finishing basement, insulation questions

My house is new construciton (built in 2007) in the Watertown NY area and I have no A/C in the house. If you know upstate NY you know why we don't have A/C.

I'm planning on finishing the basement and want to do it so that I reduce the risk of mold as much as possible. The foundation is all concrete block walls with no exterior or interior insulation. I plan to put a tyvec vapor barrier against the concrete wall then my R13 insulation then the sheetrock.

My overall question is; is this the most efficient/cost effective way of insulating while reducing my chances of mold growing?

Thanks in advance for any input.
 
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Old 07-20-09, 07:57 AM
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First of all, forget the vapor barrier against the basement walls. Don't even use negative waterproof coating.

All vapor barriers do is to trap moisture behind them, as they do not keep moisture from infiltrating the porous concrete walls through capillary action. Once you finish the wall there is no saying what is going to happen behind that vapor barrier.

According to the U.S. Dept of Energy - EERE recommendations through their Building America initiative as well as Building Science Corp. typical moisture in basement walls and floors should be allowed to evaporate and dry into the basement.

You also did not mention what kind of insulation you are using, but I would not recommend fiberglass, for two reasons:
1- It soaks moisture like a sponge and wet fiberglass looses all its R-Value.
2- Fiberglass is usually held together by an urea-based adhesive. Urea is an organic compound. Organic matter + moisture = mold.

For basement insulation, EERE Building America, recommends the used of closed cell foam board insulation directly against the walls as best practice.

Actually if you can, avoid using anything organic and water absorbent in basement finishing, including wood studs, wooden floors or sub-floors, drywall.

Unless you plan to remodel your basement often, look for inorganic and 100% waterproof finishes that are capable to withstand humidity and that will not get ruined in case of a basement flood or a water accident burst pipes and washing machine hoses, leaky water heater tank, etc)
 
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Old 07-20-09, 08:29 AM
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Unfortunately CyFree is correct, but you are fortunate, you are here before the project is all completed, which happens all too often. The good news is, they have learned a lot over the years about how to and not to do basements. Especially in these air tight, energy conscious times.

Here is some reading: BSD-103: Understanding Basements —

Attention to air sealing and insulating the rim joist area and foundation areas exposed above ground. I usually extend to one foot below grade and leave below that as is.

You will se the link likes rigid insulation as CyFree suggested. There are surface grinders that can make short work of preparing a smooth surface for the foam board.

This will get you started. More questions welcome.

Bud
 
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Old 07-20-09, 09:45 PM
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Based on that article the most cost effective way is to use Rigid vapor semi-impermeable insulation behind the stud wall then insulate the wall cavity with unfaced fiberglass. Should I leave a gap between the rigid insulation and the concrete wall, or does it really matter?

Is the mold resistant drywall of any real use or is it more money for no real value?

I guess the point is don't try to fight the water/moisture, just try and manage the best you can.
 
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Old 07-21-09, 02:49 AM
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Manage is correct as all basements will/do have moisture. Just helped on a small basement where they chose the paperless. The thinking was to avoid providing any food. He installed I taped, getting too old to throw that stuff around. Only issue was the surface, had a cloth like texture and where the mud was applied it was nice and smooth. Tested with paint and really noticable. Had to skim the entire surface with a thin coat. Probably should have thinned and applied with a roller. Came out nice and don't have to worry about any future moidture problems. As for insulation, you won't need any extra below grade and the studs can be up against the rigid or set off. Max 1" rigid below grade as the perm goes down with thickness. If you are air sealing the entire basement, you will need to provide a combustion air source for your furnace/boiler. At some point it would be good to have a pressure test to make sure dryer and other fans don't don't steal the needed air.

What started out simple, finishing a basement, becomes one of the most technicial projects you can undertake.

GL
Bud
 
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Old 07-21-09, 03:53 AM
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thanks for the response Bud,

What do you mean by air sealing the basement?
 
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Old 07-21-09, 04:54 AM
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The outer perimeter of the box formed by the floor joists (basement ceiling) is called the rim joist. The cracks and crevices created in its assembly and where it sets on the concrete wall is often a major source of infiltration. Also, since stack effect is a 24/7 flow of air, with warm air exiting the upper levels and being replaced by cold air entering the lower levels, this rim joist is a noticeable source of cold air. The link provided shows some detaining to insulate this area at which time the application of some can foam will seal things up very well.

Again, although it seems counterproductive, make sure you have a source of combustion air for the heating sys. Newer units have or are capable of having a sealed source of combustion air. Worth looking into.

Those of you who are young enough will almost certainly encounter energy costs that are off the scale. Russia and China are becoming rich on energy revenues and are spreading their influence around the world, essentially buying up future sources of energy. On the other hand, we are becoming poor due to our excess use of a commodity we have to import from others. So how much insulation do you add? Our current government is considering REQUIRING all homes to be brought up to energy star standards. Rules to that effect are already in place in some areas.

Sorry for the speech.
Read up on HRV's and ERV's and have a radon test done before and after.

GL
Bud
 
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Old 07-22-09, 06:32 AM
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Bud is correct in his recommendations, specially concerning sealing the basement and the need to provide a consistent air supply for furnace and combustion appliances.

That is a biggie. You do not want to depressurize the space with those appliances there. And of course there is always the carbon monoxide concern. I hope you consider have detectors down there and around the house if you don't already have.

Bud, excellent take on US's energy efficiency problems. And when it comes to homes, I was reading an interesting an interesting article that says that basically, heating and cooling technologies are about as energy efficient as they can get at this point, but we are still far behind, because we overlooked insulation, air sealing and moisture control for way too long.

Just do you know, racinnation, the U.S. Dept of Energy reports show that you can get enormous energy savings with basement insulation alone. That means that besides having a nice finished room, you will be saving some money in energy bills...
 
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Old 07-22-09, 07:11 AM
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Thanks for all the input; I didnít realize finishing the basement would have to be such a well planned operation.

Concerning the furnace; my furnace is Propane and in the basement. It currently draws fresh air from 2 locations on the main floor of the house and from the basement. Is the fresh air return what you are referring to as combustible air?

I also have a Pellet stove located in the basement; does that play a role in the efficient use of the furnace as far as the combustible air quality is concerned?

I'm currently working on drawing all this out in AutoCAD; I'll post an image tomorrow so you can better visualize what I'm talking about.
 
 

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