Another crawl space…
I would like to improve upon the poly vapor barrier that exists on the dirt floor of my crawlspace. I have read the ‘crawlspace article’ penned by Martin but have some specific questions.
First, a description of my situation. A full basement under the ell of the house leads to the crawlspace under the main house, which is accessible via a ‘basement window’ (the frame of the window exists, the window does not). Roughly 3 and half walls of the crawlspace lie on the outside of the main house (the remaining wall falls under the junction of the ell and main house). The ‘exterior’ walls of the crawlspace are granite blocks which have been sprayed with closed cell foam, the rim joists have been sprayed as well. The remaining portion of the crawlspace wall consists of a cement ‘hallway’ between the basement and the crawlspace access point and a rubble wall. In general, there is no foam on these interior walls.
1.) I would like to use the poly that has been placed to the extent feasible. It is likely 6 mil poly placed over the uneven floor of the crawlspace, including some rocks. Any problems so far?
2.) The existing poly on the floor of the crawlspace was sealed to the exterior walls by the foam in some places but it is not attached to the foundation walls along most of its perimeter. Lacking a convenient way to attach the poly to the foam or the concrete block/rubble wall, is simply placing bricks/rocks on top of the plastic sufficient from an overall moisture management standpoint? If not, do you have any other ideas for effectively anchoring the poly?
3.) The edges of the poly sheets were not taped where they overlap. What is a good tape to use for this purpose? In the crawlspace article I read it indicates using a compatible tape or mastic. What, specifically, would be considered compatible with poly?
4.) The poly has some small holes in it in some of the more traveled portions of the crawlspace. Will the relatively small number of defects seriously undermine the performance of the barrier? If so, could taping them be sufficient and keep me from having to install new poly?
5.) If I were to install new poly, would it be unwise to install the new material over the old?
6.) Given the configuration of the crawlspace relative to the basement, what might be the best way to incorporate an exhaust fan? There are 2 basement windows along the exterior walls of the crawlspace and 3 in the full basement. Should I incorporate a fan into one of the crawlspace windows and replace the window between the basement and crawlspace to (sort of) isolate the crawlspace (the rubble wall is hardly airtight) or something else?
7.) Looking on the internet, most of the exhaust fans I see move air at much higher rates than needed for the crawlspace (estimated at ~20 cfm for the ~900 sq ft crawlspace). Any ideas who might make more suitably sized fans?
Thanks a bunch!!
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