Crawlspace preparations for moisture control

MurphyMan

I am just completing a 3/4"x3-1/2" oak installation in the 30 y-o house we just bought. So far, so good and we are pleased with the outcome, consider ing we have no previous experience.

The subfloor is 3/4" plywood, over a crawl space. The 1,200 sq. ft. crawlspace has clear plastic over gravel, but it is torn in spots had has generally deteriorated a bit in spots over the years. Also, the crawl space vents seem to be partially blocked.

I want to make sure that the floor stays nice and flat, so I am planning on having the plastic replaced next week. I see that I am supposed to use 6 mil black plastic. Just curious, why black and not clear?

Any other recommendations? I am planning of completely removing the old stuff, then installing the new.

FYI - have read this thread: Cupping of wood floor, need input and it got me thinking.

Ed911

I'm also interested in hearing comments here. I too need to put down some plastic moisture barrier.

fixrite

black plastic as opposed to clear plastic is better in this situation as clear allow light to contact the ground and promote growth )of plants weeds etc) which is NOT what you want. In regards to your crawl space you can do one of two things, treat it as a heated area (which means heating it) or allow it to be a cold zone and have it vented and then apply insulation in your flooring to reduce the temperature difference. I would also install a vapour barrier to reduce the moisture transfer between zones. Knowing what your humidity is in your home also helps you in reducing cupping and swelling of your flooring. Have seen it where it has heaved the floor almost 2 inches. Not trying to scare you but knowing what you are up against is always a good thing. So installing a humistat in your home allows you to monitor the humidity in your house as well as making what ever changes are necessary.

fixrite

Just where do you live as it makes a big difference.

MurphyMan

We are in southern Illinois. 90 SE of St. Louis.

My flooring supplier just gave me a complimentary relative humidity indicator - not calibrated of course.

Typical humidity right now is reading abound 41%.

CrawlSpaceMoist

41% in the air of the crawlspace? That sounds pretty good.
I prefer the clear plastic. if you're concerned about 'stuff' growing under the poly and light shining through it... how much light do you have in the crawlspace and do you have any plants sprouting down there in past years? If seeds aren't getting beneath it when it's in bad shape, it should be even better when you get a new poly, wall-to-wall and pinned in place.
6mil is typically what's required by codes as a minimum - just check with your local code enforcement office.
And the reason I don't like black plastic? Hides critters! With a clear or white poly you can see what's going on. Black, you could have anything down there and not see it until you crawl up on it.
Finally, a 'vapor barrier' between zones. I'm assuming they're talking about in a vented crawl space adding a vapor barrier at the bottom of the joists. Be careful! This could potentially trap humidity from the home beneath the floor and cause a lot of issues. Likely, probably not. But possible.

fixrite

Moisture barriers are normally installed on the WARM side of the wall floor ceiling etc. If you wanted to you can install a vapour barrier on your floor underside. This would mean you would have to wrap the floor joists and have the vapour barrier follow the underside of the floor. This is not easy to do but does provide the moisture barrier that in a high humidity situation is necessary to do. If the relative humidity indicator is not calibrated correctly, then you could be setting yourself up for future problems. If you do not heat your crawl space then you will need to ensure it is vented correctly based on the square footage of your crawlspace. Then install a good vapour barrier and some roxul insulation held in with strapping. That will isolate the humidity and provide a barrier of insulation for your living area above. Your other choice is to hire a company to install spray foam which would both seal it and give you the insulation you require. Can't remember which one is to be used in this situation ( open or closed cell spray foam) but that is easy to find out. If you had the funds I would suggest the spray foam as it is the best product for this situation. Check your area and get a few quotes along with a history of the company. Hope all works out well for you.

DrumBum

i would also suggest louvered vents in your crawlspace that open and close with temperature changes

MurphyMan

Here is an update.

Since I never seem to know when to stop, I have decided to fully encapsulate the crawlspace. Much of my information is from here: http://crawlspaceinfo.com/Crawl_Spac...nditioning.htm

I got a quote from a local company and they wanted almost $7K for the job. I ordered materials and will get it done for less than $1,200. I am going the whole route; sealing the vents, wrapping the piers, and sealing the floor.

I think it will have an overall benefit to the house.

There is a lot of information about the benefits of encapsulating the crawlspace, and I think it's the best way to go.

Gary in WA

I didn't see that ad mention termites anywhere.... If you run plastic up the wall, have a few inches at the top for termite inspection, if you are in any areas with them, ask locally: http://termites101.org/termite-basic...ites-by-region

http://www.fpl.fs.fed.us/documnts/te...entilation.pdf

With the foamboard on the wall, and the ground plastic vapor barrier taped to that, you still need to condition the (air) space, per minimum Code: http://www2.iccsafe.org/cs/committee...E_06_64_07.pdf

If the HVAC ductwork is down there, it may be better to insulate the floor- pp.3; http://www.advancedenergy.org/buildi...l%20Spaces.pdf

This covers most of it, hit F5 if it stops; http://www.buildingscience.com/docum...ance-and-codes

For damp vented crawls: http://www.buildingscience.com/docum...n-crawlspaces/

Need more? just ask.....too late now.

Gary

__________________

MurphyMan

Thanks, Gary.

In the old installation, they had barely glued the foam board to the cinder bloc and they placed it so it came even with the top of the block. Incorrect method, I know.

I went under yesterday and found I can easily pull each piece of foam board off, and better yet, if I set it on the floor, I have a 5" gap at the top.

This makes it a lot easier, I had feared I was going to trim each piece of board. I'll just re-glue the board to the lower position and leave the 5" gap. Two of those five inches will be used to attach the barrier, leaving three inches for termite inspection.

I am going to condition the airspace. Not sure how to interpret the numbers, but I am planning on cutting two 4x12 holes in the duct work at opposite ends of the crawlspace. One for supply air and one for return.

I start work on it in earnest in three days.

Sam

Sammy 2

I used a product called Stego Wrap for a vapor barrier.

pucks101

I like that encapsulation idea. My crawl space is much nicer now that I made it a "heated space". The idea of ventialting a crawl to the outside through a couple little screen vents is just a failure...