Protecting Exposed Subfloor From Build Up Of Water - Painting - DIY Chatroom Home Improvement Forum

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Old 07-25-2011, 12:45 PM   #1
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Protecting exposed subfloor from build up of water

Hi all,

Im looking for a method to keep water from accumulating on a platform-like-floor-system I just built. The platform will eventually have a small cabin sitting on top of it, but that cabin wont be raised and closed in for a number of months (anywhere from 4 to 9).

My dilemma is this: The subfloor is 1" rough sawn hemlock boards, but between them and the joists is housewrap with taped seams. The joists will eventually be dense-packed with cellulose, so the housewrap will 1)help contain the cellulose when its blown, and 2)act as an air barrier. However, the hemlock boards have shrunk considerably since they were laid down, which has opened up fairly significant gaps between them (1/2" in the most dramatic places). Whenever it rains, water gets between the hemlock boards, and pools up on top of the housewrap. This makes it so the hemlock boards are sitting on top of and around water. I want to do something to stop this from continuing to happen.

The added layer to this dilemma is I am currently living over a portion of this platform in a canvas wall tent, so tarping the whole thing is not the most desirable option at all (dont want to live and walk on a tarp or poly all the time).

So, I'm looking for options to prevent this accumulation of water. Here are the options I can think of:

1. Tarp the whole thing once there's no water on the housewrap, and either deal with living atop it, or live somewhere else.

2. Lay down tarp everywhere but the area covered by my (large) tent in such a way that I can easily roll it up and down, so that the tarp isnt neccesarily covering the platform at all times, but only at certain times (night, rainy periods, periods of expected rain, and when we're away for extended periods of time).

3. Lay down 3/8" underlayment plywood over the whole thing, with caulked and taped seams, and put down a coat of primer or some other effective water sealer (any suggestions on what in particular?) over the whole thing. Keep it uncovered until winter approaches, and then tarp the whole thing (if there isnt a structure over it yet) before the snows come.
  • a) Would this work? Would primer or another sealer actually be able to prevent the plywood from deteriorating while exposed for a number of months?

Any other suggestions? Opinions on my current options? Personal experiences?

Any suggestions appreciated, thanks,


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Old 07-25-2011, 06:58 PM   #2
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That house wrap and the water that it traps will destroy the hemlock before the cabin is finished.

I think you should slash the house wrap down the center of the floor joists---you could tape it together later--but at least the decking will dry out from underneath.

If you can't stop it from getting wet--at least give it all the help you can to dry out.


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Old 07-26-2011, 08:04 AM   #3
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Thanks for the reply.

Yeah, I think I'll have to do that. I just dont know what to do to keep the joists and anything else from rotting in the process. Under the joists, in the joist bays, are pieces of plywood to act as a floor to catch the cellulose. Even if I poke some holes in the housewrap and take off the rim joists (which Im about to do today), I hope the rain water wont rot out that bottom layer of playwood.

We'll see I guess.

Man! I wish I had realized all this sooner.
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