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Crawl space weatherizing

Posted by braytonak (My Page) on
Sun, Sep 9, 07 at 16:23

I just finished reading a similar thread, but think that some of the points made don't apply to my situation.

An Energy Rater looked at my home and said the crawl space (exposed foundation walls, approximately four to five feet of height with unsealed sheets of plastic strewn on the sandy, 90% dry, ground) is where I could make the biggest improvement. He gave me a diagram that shows what I should do. This is all fine and dandy, but it made me wonder. Here's what the diagram says to do:

1) Lay vapor barrier across the exposed earth floor and seal with caulking at all edges and penetrations.
2) Apply vapor barrier to foundation walls and seal with caulking.
3) Install insulation over the foundation walls, as well as on ground inward from the wall for four feet.
4) Seal the perimeter of the floor joist area with styrofoam sheets and seal.

This is all based on a climate that can see -20F days. The crawl space is partially conditioned, as in it gets its heat from whatever leaks from the heating pipes, hot water pipes and through the floor. Ventilation is allowed in the summer (May / June through September) through two naturally aspirating vents in the wall.

This sounds to me like a way to actually create problems with mold under the barrier or behind the floor joist perimeter.

My biggest questions are A) Should I really be sealing a crawlspace to the point that it could become a swimming pool, B) Should the walls have traditional faced or unfaced fiberglass insulation, 2" styrofoam panels (faced with foil) or some professionally applied spray-on foam, which probably eliminates the need for a vapor barrier on those walls?, and lastly C) How would those insulating products be attached? There is currently about two feet of insulation that is stapled to the horizontal framing on top of the cement foundation, which is then just hanging over the wall. (Doesn't reach the ground by any stretch of the imagination.)

Thanks to anyone who makes it through my lengthy questioning!

Follow-Up Postings:

RE: Crawl space weatherizing

Look at the Building Science website, they will have a lot of info on the why's and how-to's to accomplish what the energy rater has proposed. Also, they will suggest that you keep the crawl vents closed/sealed and make the crawl into a conditioned area, like you would a basement.

If the crawl is assembled and sealed properly, it shouldn't become a swimming pool; drainage and a sump pump/pit can always be incorporated.

Yes, spray-on foam can accomplish the sealing and insulation function with one product, but it is a pricey way to go. You will have to be the one to determine if the cost is right for your situation.

Here is a link that might be useful: Bulding Science paper: Conditioned Crawlspaces

RE: Crawl space weatherizing

Thank you for the information! I'll have to analyze that document closely. Perhaps the State has similar information that can point out any differences for this climate.

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