Insulating a crawl space, and frozen drain pipe

hjihjiJanuary 28, 2007

We recently had the kitchen redone in our 1840's Vermont farm house. The kitchen is over a crawl space. Before the remodel, insulation had been pushed up in between the floor joists and held into place with netting of some sort. Now, we know it's not enough insulation and want to add more. My contractor, who works exclusively on older homes (remodeling; not tearing down and rebuilding) suggests that we add more fiberglass to what's there, and then cover it all with foam board insulation. His reasoning for this is that the foam will seal everything in, making it airtight (if done correctly), and it will keep the mice out of the insulation.

I'm not sure this is the best approach to take. It seems like the foam board won't be providng much R-value, since it would be too far from the underside of the floor. Instead, it seems like it would be more of a support for the insulation, something that could be accomplished much more cheaply with some plywood or even plastic tarps, stapled in place. If I were doing it myself (which I never would), I would pull out all of the old insulation, put 1" foam board up against the floor, caulk it in place, cover that with batts of fiberglass, and then cover all of that with tarp or plywood.

Please give me your thoughts on this. The reason it's an issue right now is because our drain pipe has frozen and the water is stuck in our sink (it's been below 0F for a week or so). We never had this problem before the work was done, and so I think that the insulation that was in place before the remodel, has been disrupted and isn't keeping the pipes protected any longer.

We have heat tape against our water pipes, but not against the drain pipe. Thank goodness.

Thanks for any thoughts/wisdom/critiques you can offer.


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R value is cumulative and does not depend on distance from the heat source.
Foams have some of the highest R-values per inch available, and cost like it.
If correctly done his proposal makes sense.
You need a very good seal at the outside of the foam to prevent moisture entry since it will act as a second vapor barrier.
Luckily most of the vapor in a crawl space comes from the earth and not the interior.
Air infiltration casuses a lot more heat loss than less than adequate insulation.

    Bookmark   January 28, 2007 at 12:09PM
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Depending on cost, you might want to consider blowing in icynene. I did it under one section of my house and the floors are notiecably warmer. So much so, in fact, I am blowing it under the rest of my house. Its pricey, but effective and needs no vapor barrier.

    Bookmark   January 30, 2007 at 10:13AM
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I have a similar problem.

Wianno, icynene is an interesting idea. As you note, it's pricey. Does anyone know if there any similar products that I can spray on myself (to save money)?

    Bookmark   January 30, 2007 at 12:23PM
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There is a product called tiger foam which is a closed cell product. Icynene is open celled. Tiger foam is like Great Stuff in 20lb propane type cylinders, and DIY. See their web site, I never used it before and know nothing more about it. if you use it, post back your results!

Do the research on open v closed cell. Not sure wht is best in what application

    Bookmark   January 30, 2007 at 4:33PM
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