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Posted by The Insulator on February 21st, 2000 06:37 PM
In reply to I'm with Jay, please explain by bc on February 21st, 2000 04:42 PM [Go to top of thread]

The thinking on crawlspaces has been to vent them w/ closable vents. The Idea was to open the vents in the summer & close them in the winter. The problem w/ this is that by venting in the summer, your opening the cool crawlspace to the hot humid outside air. The net result is bringing moisture into the crawlspace. When the hot humid air hits the cold surfaces, condensation results.

On the other hand, if you reverse the venting (Open in winter / Closed in summer, you stop the moisture from entering, but create other issues. Obviously, you would need to insulate the floor & plumbing, & heat tape any plumbing outside you thermal envelop (if water doesn't flow, all latent heat will dissipate & freeze the lines). Also, your now exposing your foundation to the cold, opening the possibility of lofting & shifting the same as experienced in mobile homes. Another factor is that unless you have in floor heat, the floor will be cooler in the winter because the heated air will rise away from the floor, never allowing it to fully warm with the rest of the house.

By insulation the perimeter (preferably with foam board, since it is also a vapor barrier) and installing a vapor barrier on the ground, you don't need the venting since your preventing most of the moisture from ever entering the crawlspace (95% vapor barrier coverage solves 95% of the problem). The only factor that would create any difficulty is if you have leakage or water draining into the crawlspace, then it's best to solve the problem & not the syptomn.

At this point, your best to include the crawspace in your heating system (if you have forced air, perhaps install a register). This would keep everything warmer, including the floor. Again, you wouldn't need to vent this anymore than you would any wall in the house.

I hope this helps

The Insulator

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