http://us.f1.yahoofs.com/users/adefc3e/d572/__tn_/c787.jpg?phzJYlBBH06nT2xN

We removed this board and another 120 s.f. from a floor that has the 6-mill poly on top of the plywood subfloor, then 30 pound felt. There is a 2' crawl space with no ventilation underneath. The nail did not rust above the poly and the floor did not buckle. The floor joist rotted and the plywood subfloor is wet and full of termites but the vapor retarder kept the moisture away from the flooring, This floor was installed in the early 80's and still looks new, everything under the flooring is shot.
It looks like the poly and felt sealed around the nail and stoped moisture from getting to the flooring. Every day is a new experience.
Buddy

Well, I will have to practice with this photo thing.
Buddy

I'd like to see that. Send it to Ken. I take it the dirt under the crawl space was not covered or was it?

I wondered what Buddy was trying to say when all I saw was this picture in my mailbox. I thought "okay what now," until I saw his message here.

I always thought using poly was a no-no with a wood subfloor? Promotes mold growth doesn't it?



Btw, I changed the title Buddy

When I was just starting out and the NWFA was not yet formed, my employer had us use poly over wood subfloors. He told us this was to stop moisture from getting to the oak floors. It wasn't until I became licensed and began to work for myself that I found out that this is not recommended. As you know, there are no building codes for floor covering so it was never explained that this could promote rot. Vapor transmission is one of those controversial subjects. In some parts of the country, they install plastic to the wall studs before covering with sheetrock. Is this good or bad? Personally, I think the position NOFMA and the NWFA take make sense. In case of moisture in crawlspace, eliminate the source first. Then look into vapor barriers placed on the earth. There are some types of crawl space areas that are sealed up (which I think is a bad idea) so if there is moisture build up, where is that vapor going to go?
In the case of Buddy's job, it looks like it was trapped in the crawl space and promoted rot and termites. What's worse, replacing a floor or replacing subflooring and floor joists. That house was probably constructed improperly to begin with with no crawl space ventilation and poor lot drainage. What is amazing is that no moisture or termites made it to the oak floors. I guess plastic isn't very tasty to termites.

Ernesto, The dirt is not covered with poly, it would have been underwater anyway. They are going to cover it now and correct the water buildup problem.
Ken, Yes there is mold and mildew everywhere under the plastic. Some of the fiberglass insulation is hanging to the ground and water has wicked up to the floor joist.
And Gary, The lot drainage was blocked with lanscape timbers and dirt piled against one outside wall blocking the water under the house.

It sounds like you guys have been there.
Buddy

I got a question for you guys which follows along the same idea.

Whats the difference if you glue a sheet of vinyl flooring on top of a wood substrate as compared to using poly under a wood floor over a wooden substrate?

Would potentially cause the same problem yet you never here of the floor rotting because of a vinyl install do ya?

Ernesto,
You bring up an interesting point. While polyethylene and sheet vinyl are not the same thing, I wonder what the perm rating would be for each? Way low, I'm sure; and that is what matters in this instance. Keep in mind that it is NOT the poly film that causes rot but the excessive humidity in the crawl space. I've seen homes less then 10 yrs. old with their pony walls rotted out because their crawl space was like a swamp. And this was over homes with carpet that had no vinyl or wood to trap moisture in the subfloor. Independant studies have shown the value of installing a 6 to 8 mil vapor barrier on the ground, whether one gets a wood floor or not. In a scenario where there is an existing vinyl kitchen floor over a crawl space that is damp and the owner wishes to have wood installed in it's place, it probably would not matter if one installed a poly film under the wood floor as this would not change what is already happening. However, the wood installer would be exposing himself to liability. And keep in mind that expecting a plastic film on a subfloor to totally protect the wood from moisture is a crap shoot. Homeowners with crawl spaces are well advised to ensure the space remains absolutely dry year round or install a poly vapor barrier.

Exactly Gary. Which brings us back to the NWFA's position on using a plastic barrier/retarder under wood. I thnk its a moot point. The focus being on the dryness of the crawl space or basement being the primary consideration.

It is not quite that simple,Stephen. Plastic is not a retarder. It is a barrier.

Therein lies the important distinction. Felt backed vinyl or roofing felt will diffuse moisture. The diffusion of vapor is key. Retarders give the vapor sort of a staging medium,for lack of a better term. Plastic has no capacity to do that. It forces whatever is under it to keep all of the moisture.

KnowutImean?

KnowutImean



Have you considered condensation into your barrier theory?

Or could we call it a moisture attracter?

What I stated,Perry, is not theory. If you have an idea to share,or a criticism of what I have stated,why not simply post it?

Even through all that adhesive Chuck? Ya sure? What about gas bubbles in vinyl? I'd like to test that theory someday. How would you test that Chuck?

All that adhesive? WTF are you talking about? Bubbles from what? Water vapor? All gasses dissipate at some point. The permeabitily of the material that constrains the gas is the variable. Helium balloons eventually fall to the ground due to dissipation.

Methinks you are ignoring the felt backing part of the equation.

All gasses are not equal in value. Some are more volatile than others.

Are you just screwing with me,or would you really like an explanation?


Food for thought:

Why is vinyl seam sealer stored in glass?

Some dessert.

How is it that ice can evaporate at below freezing? It did not melt. Must be gaseous in nature. Try it with an ice cube in your freezer.