Crawl space water proofing

[Ivan Vegvary]

Got most of my crawl space dug out to 42 inches so I can move around. Time to put plastic sheeting on the dirt. Got some 6 mil from HD. What's the best way to handle this 20 foot wide material. I ended up putting intermittent footings under the floor system on about 8 foot centers. Do I cut 10 foot strips above ground, drag them down there and run up the the sides of the footings, leaving enough overlap for the next 10 foot strip? Do I tape the seams together or use construction glue? What do I do at the foundations (edges of the house)? Should I lap up high enough to staple to the sill plate? Should I glue it to the sides of the concrete foundation? I'd like to make this as easy as possible. Suggestions from anyone that's done this would be greatly appreciated.

Thanks, Ivan Vegvary

[Tony Hwang]

Hi, Wonder why you need to do it? My cabin has crawl space(high enoungh I can sit up working on furnace, hot water tank, well pressure tank, etc. Walls are R20 foam insulated, floor is bare dirt which is always dry. Area has good air vent for furnace. If you have moisture problem wouldn't it trap moisture?

[Ivan Vegvary]

Hi Tony, Thanks for the reply. I don't know why I'm doing it either. Every book I read, web site I visit indicates that ground moisture should be sealed at the ground level and not allowed to penetrate the crawl space. Here, in the northwest, everybody covers their foundations vents during the winter due to thermal losses. I think this traps the moisture within and plastic sheeting is the preferred method to prevent moisture in the first place.

Ivan Vegvary

[Malcolm Hoar]

I'm not sure I would bother. At least, I haven't in my home.

Does your crawl space get really damp? Standing water? That's a problem but plastic sheet on top of the dirt isn't really going to solve your bigger problem.

If the dirt is nice and dry like mine, why bother with the plastic?

Since you're already messing around in that nasty space, it is worth ensuring that you have really good ventilation. That's much more benefitial than a sheet of plastic on the dirt.

I do have a vapor barrier between the sub-floor and my hardwood flooring, but that plays a somewhat different role.

[mm]

In Indiana we had metal louvers spaced along the foundation that let in air to the crawl space, which we were told to close during part of the year. (Winter or summer, I forget which part.)

We only went down to the crawl space once in 8 years, and that time I didn't walk even one step from the hatch, because it was one big mud layer. I was 10 and didn't have any money, so I didn't think of putting down vinyl, which probably cost a fortune then. Of course our crawl space was wetter than many or most. One corner of our yard was practically a swamp in the spring and it was four feet higher than the bottom of the crawl space.

Sorry, that's all I know. I don't know if you need vinyl or not.

[terry]

book I

Be careful not venting a crawl space such as that. Our first house (about 900 sq.feet) we did have small vents to permit cross draft of the crawl space, ther was also a furnace venting air up the chimney. No problems for 11 + years. A current neighbour did not vent and did not seal then ground below in his crawl space and now has rot problems in the joists and ledger boards of one corner of the floor above. The floor has dropped. My relative has similar situation to the OP and has had to install a continuously running vent fan to get the moisture down to a reasonable level!. My suggestion would be to put down heavy plastic and put some gravel over it.

[Wayne Boatwright]

On Wed 11 Nov 2009 10:49:01p, mm told us...

The bottoms of most homes built over crawl spaces today are completely sealed against moisture infiltration. Our home is 3 years old, and I remember the contractor providing us with a special 4" wide sealing tape to use in case we had occasion to penetrate the barrier.

Having said that, we have a totally moisture free crawl space, as we live in the desert. There is a ventilation shaft at each corner of the house, as well as a larger shaft for entry into the space.

If I felt I had to seal something, it would be the bottom of the house, not the dirt on the floor of the crawl space.

[teabird]

All these comments are good for thought, but if you are going to proceed it doesn't have to be complicated.

We just had an addition put on and they groomed the dirt flat then dropped on a heavy duty plastic. I'm sure they got theirs from HD too. Cut the plastic so it's easy to handle, I'd lay it out and cut around the footings. No tape, overlap the edges by about a foot or so, and right up to the foundation. A few rocks on the corners to keep it in place wouldn't hurt but aren't needed. My guy said they are shooting for 85% coverage.

I keep my vents open all year round.

[norminn]

You probably should not staple it to the sill plate or cover the entire inside of the wall....you need to be able to inspect inside of the wall for termite mud tubes.

[ALE]

Old thinking was to allow air into the crawl space. Many city codes required so many sq. in. of vents per sq. ft. of 'floor' crawl space.

The latest thinking is to seal the crawl space.

See the US Government recommendations here:

ALE

All these comments are good for thought, but if you are going to proceed it doesn't have to be complicated.

We just had an addition put on and they groomed the dirt flat then dropped on a heavy duty plastic. I'm sure they got theirs from HD too. Cut the plastic so it's easy to handle, I'd lay it out and cut around the footings. No tape, overlap the edges by about a foot or so, and right up to the foundation. A few rocks on the corners to keep it in place wouldn't hurt but aren't needed. My guy said they are shooting for 85% coverage.

I keep my vents open all year round.

[ALE]