Hi Everybody. great board here.

We are installing 3/4 white oak prefinished tongue & groove in a small cottage which has a crawl space (24 + inches) & no vapor barrier. We did moisture tests by taping down plastic, and there was no moisture, but often, the air in the house is damp. The subfloor under the carpets we pulled up was good, and we only had to replace one piece of the plywood. Above the crawl space the floor is 3/4" plywood, tar paper, then 1/2" plywood. I plan to use another layer of tarpaper, but was wondering id there was any annitional benefit to adding a layer of red rosin paper. I'm alsayws worried about moisture in the future.


Any suggestions. The wood is acclimating even as I write and will be sitting for 2 more weeks.

All solid wood floors that are nailed down over a crawl space (which you have) REQUIRE a 6 to 8 mil polyethylene vapor barrier to be installed on the GROUND in the crawl space. One needs to cover ALL the earth, overlapping the seems by about 12". Weight the plastic down with bricks, rocks, sand, etc. No organic materials (ei. wood) Also NWFA and NOFMA expect a 15 lb. asphalt paper as a moisture RETARDER ( Not Barrier) laid on the subfloor prior to the installation of any nail down floor. That red rosin paper is worthless as a vapor barrier. Wood subfloors need to be within 4% moisture content of materials for strip flooring, 2% for plank flooring. Cross ventilation of the crawl space is equally important, as is lot grading and drainage. If the earth in the crawl space is now damp or wet, you can expect problems with your floors. It must be dry!

Thnaks, Gary. I suspected as much. Was going to add the rosin paper over the tar paper just to make the installation easier and the boards easier to slide. I'll look into the vapor barrier.

I hope you mean by looking into the vapor barrier you mean one will be installed. If you don't prepare for your floor to cup.

Please,for your own sake, heed Tandy's advice.

Plastic over the dirt is NOT an optional requirement. It is a must. Plastic stapled to the joists from underneath is not a bad idea,either.

Yes. we are installing a 6 mil vapor barrier next week. i've heard varying theories on how to fasten it to the cinderblock walls. some have said use plastic expansion screws. some say use a pieces of wood screwed in along the edges along the perimeter, then a bead of caulk where the plastic meets the wall. any advice?

Don't use wood in a crawl space. It is organic matter and could attract termites. If you must use wood, at least use pressure treated. The NWFA doess't consider attaching the plastic to the walls that important. Simply let the plastic extend up a few inches and weight it down with rock, sand, bricks, old chunks of concrete, etc. If you have enough foundation vents (should equal 1.5 sq.ft. of vent openings per 100 sq.ft. of total floor space) then any little amount of vapor that gets past the plastic will be carried out by the foundation vents. BTW, BLACK polyethylene is preferred over clear. Good luck!

Thanks for the info gary, and all of your help. I'm doing as you suggest, and the builders vapor barrier is an opaque blue, bot black, but it's not clear for sure. I'll use pressure treated wood.

But we have no wents in the baasement, and we live in such a cold winter region that we have opted not to install them. P.S> I know this is the subject of a GREAT debate.

judy

I did not know a basement was involved. Is the floor of the basement dirt? If this is a basement and not a crawl space all we have been telling you does not apply. I will hand my answering of what you should do in your area with basements that are not climate controlled.

soryy everyone. it's a crawlspace, NOT a basement. you 've all been giving me great advice. the whole house is about 900 sq ft overall. there is an exposed dirt floor in the crawlspace (over about 80% of the space ) there is a poured concrete floor (about 8 x 10') in the front portion when you walk in the door. it's one of the nices, cleanest crawlspaces i've seen. the front portion where the concrete is, has a clearance of about 48". the REST of the crawlspace is definitely just that. the clearance in there varies from 36" to, yikes, 24" in some parts. i'm worried that i won't have enough room to manuever in there, that's why i was considering using the wood strips to attach the plastic. i think it will be easier, and faster, overall to secure it that way. i like the idea of the expanding plastic bolts, but i think it will be very hard to do, given the clearance.

i've been checking out websites, and this one seems comprehensive. take a look...

http://www.taunton.com/finehomebuilding ... h00107.asp

thanks for your help.

Very good article from Fine Homebuilding. Don't think I've ever seen anyone go to such lengths as the author in sealing up a crawl space. One thing, did you catch the sentence where he said he removed "all organic matter before sealing up the crawlspace". If you want to bolt the plastic to your walls, fine. I'd rethink using wood though. Best of luck.

yes. i saw that part. guess i'll continue the search for an alternative. if anything comes to anyone, give me a shout. jusipo@aol.com.

hey all...i posted this question well over 5 years ago. i followed the advice and am so happy to report that MY FLOORS (3/4 prefinished bruce hardwood)over a crawlspace with no cross ventilation ARE BEAUTIFUL. no cupping. no troubles. just warm -cozy in winter and nice on bare feet in summer. finished the entire house NOTE:i did not not skimp on the plastic vapor barrier...bought construction grade, this forum is GREAT. do what they tell you.

Well, that is excellent news. You don't often get a 5 year follow up.

I know just enough to be real dangerous! Hehehehe!!

Very nice of you to come back and tell us how things went. Yes, the contributors on this site are some of the best in the industry and combined, have more knowledge than many manufacturers.