Question regarding vapor barrier

Old 06-12-15, 08:12 PM
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Question regarding vapor barrier

Hello, just joined!

I have a level lot with a crawl space. The crawl space extends under the front porch, and rain can get in between the boards. I am putting down a plastic vapor barrier, and just realized this situation.

Question - how should I handle this? If I put down plastic under the porch, rain will accumulate on it and add to the moisture under the house. Should I just put down plastic under the main part of the house, and staple a plastic barrier from the joists down to the ground where the house stops and the porch starts? This is a hundred year old house, just moved in and starting improvements.
Old 06-12-15, 08:29 PM
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I'm in a northern climate and we typically seal the crawlspace and insulate the walls. We then add heat and a dehumidifier (if needed) to condition that space. In SC you could insulate the floor and leave the crawlspace ventilated. Others that live in your climate will be along.

If the crawlspace is open to the space below the porch, are there any other vents?

Old 06-13-15, 04:01 AM
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You may want to post pictures of what you have so we can see what you see.

In the South we normally ventilate crawl spaces, but it has to be done correctly. One vent every 8' along all walls, I believe is the old Southern Building Code recommendation. The vents will be 8" x 16" so they will fit in the opening left by a concrete block elimination.

I am not sure just putting down plastic will help with any moisture problem emanating from your porch. That is why pictures will help us give you better information.
Old 06-15-15, 07:47 AM
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Fixing the rain getting in between the boards is not an option?
Old 06-15-15, 09:07 AM
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Everything under your porch should be treated like an exterior space. No poly or insulation under there at all, its outside the house. It should be ventilated since water can get into it, which was usually done with lattice or if it's brick, with some louvers. Any vapor barrier or insulation should only be done inside the house, in the heated/conditioned spaces.

The floor on such porches was usually tongue and groove which isn't leak-proof, but it was almost always heavily painted with an oil based enamel "porch paint", and sloped to the front so that it would drain. The front of the porch typically had a few 2x4 or 2x6 sized drain openings through the siding along the floor level in order to let any precipitation out.

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