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How can I create a vapor barrier between my home and its crawlspace which frequently has standing rain water that must evaporate and drain? Some first floor rooms have smelled damp for years. I am renovating the home, so now is the time to fix this.

My house on Long Beach Island in New Jersey is built on a man-made land mass crossed by lagoons. The water table is only a foot below the surface of the packed silt soil. After a rain storm, the vented crawlspace has standing water which takes a few days to evaporate and soak into the damp soil.

Most of the crawlspace floor is loosely covered with old plastic sheeting. Kraft faced insulation hung between the floor joists, but I removed it after Hurricane Sandy flooding ruined it. I found holes and gaps in the plywood subfloor for wires, pipes, and even a large hole beneath the tub drain.

How can I create a vapor barrier between this wet crawlspace and the plywood subfloor? How can I fill the various sized subfloor holes around the electrical wires and copper pipes? I will be creating a plywood box around the tub drain, but should I insulate it? Before I install bedroom carpeting, can I install a vapor barrier on top of the subfloor?

I will make a separate post about the damp smelling rooms. Thank you for your input.

Wet crawlspace two days after 1.5" of rain

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I think you have to do whatever it takes to keep that water from pooling under there. French drains, dry wells, sump pumps, etc. You can't have that standing water there and not expect mildew smells to get into the house. After the water is mitigated, you need to have the crawlspace sealed, and dehumidified.

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  • The problem is that the water table is so high. If I dig trenches to channel the water, I'd hit the saturating water that's right below ground level. I will look into french drains. I don't think I can seal the floor and walls of the crawlspace, but must leave them open so that they can drain and air out.
    – FireFox31
    Jul 28, 2017 at 13:38
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I agree with BrianK. But, your biggest problem is the plastic. That, should be removed entirely and should've never been installed, especially in that fashion. The plastic is stopping the water from seeping into the soil and the plastic should've only ever been attached to the bottom of the joists and beams, so water could come and go without affecting the building's and people's lives.

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  • Thanks. The odd thing is, the plastic has been there for at least the 25 years that I've owned the house. There is no mold on the joists or subfloor, and only the bottom row of foundation cinderblock gets damp. And during a full house renovation, I found no mold inside the walls (but some 50-year-old insulation smelled bad). For decades, this standing water has not ruined the house. But it seems SO bad.
    – FireFox31
    Jul 28, 2017 at 13:43
  • Yep, most likely the moisture has been dumping right into the house and saving the structure from visible damage...there "may" even be warping or bowing to the floors above. Similar to what's in your picture. The mold and algae looks to actually be on the underside of the plastic and likely not on the ground or gravel, probably some on top too in the deepest puddles. But, that's basically your house for 25-years. Isolate the house or keep and worsen the musty smell. The permanent fix will be blatantly noticed after a month of drying out.
    – Iggy
    Jul 28, 2017 at 15:07

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