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Old 07-28-2010, 09:48 AM   #1
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Hardwood over OSB and moisture barrier?


Installing hardwood floor. Have 5/8 particle board over 1/2 plywood as sub floor. I suppose this in not suffient sub flooring? If not, I plan to pull up particle board and replace with 5/8 OSB and screw it down. Now to vapor barrier. Subfloor is above crawl space which can be damp from time to time. Should I install felt above and below OSB to keep any moisture from getting to OSB? If so is felt ok or should I install plastic below OSB and felt above? I plan to nail down hardwood flooring.

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Old 07-28-2010, 02:16 PM   #2
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Hardwood over OSB and moisture barrier?


i didn't even think 1/2" subfloor was legal anywhere. as for the osb, have you priced it against 3/4" TG plywood? depending on what the 1/2" subfloor you now have is going over it with 3/4" TG plywood would not only stiffen the floor quite a bit, it could also get you ready for tile should you choose to do so. how big is the cost difference?

i know people do it, but i wouldn't staple hardwood over particle board, the staples don't attach with nearly as much bite as a harder subfloor. a floating floor could be an idea though

as for felt between your existing subfloor and the osb? you shouldn't be getting any moisture on your existing floor. small amounts are no big deal but constant damp is bad. the one place you do need a pad/barrier is between the hardwood and subfloor.

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Last edited by racebum; 07-28-2010 at 02:20 PM.
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Old 07-29-2010, 04:38 PM   #3
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Hardwood over OSB and moisture barrier?


I didn't think 1/2" ply was legal either, but it's there. OSB is about half cost of plywood. If I replace particle board with OSB (by nailing and gluing) then I nail hardwood down, the nails would penatrate OSB and about 3/4 way into plywood. Shouldn't that give me enough holding power with nails? Felt would then be installed only above OSB and below hardwood? I wouldn't need anything under the OSB to keep mositure from possibly coming up from crawl space?
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Old 07-29-2010, 04:45 PM   #4
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Hardwood over OSB and moisture barrier?


#15 felt is cheap and you could if it's a worry. my only comment was more or less that plywood will eventually fail if it's most as well. still for peace of mind you could easily roll #15 over the plywood and under the osb. if your plywood does start to warp from the moisture the tar paper will prevent it from getting into the osb. by the way, does your plywood actually measure 1/2" or slightly over? if so that's 5/8", 1/2" plywood actually measures .416" on a caliper or just a hair under 7/16"

now, if you never plan on doing tile the osb is fine. if it's ever a thought you have to buy that spendy 3/4" TG
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Old 07-30-2010, 08:56 AM   #5
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Hardwood over OSB and moisture barrier?


Existing plywood measures 1/2" with a ruler and no stamping on plywood to indicate thickness. No plans in future for tile. Reason I inquire about felt under the proposed OSB because there is a foil paper between the existing plywood and particle board. Naturally the builder put it there for a reason. That's has caused my question on felt above and below the proposed OSB. Thanks.
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Old 07-30-2010, 04:19 PM   #6
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Hardwood over OSB and moisture barrier?


totally agree, if that was there in the first place there is probably a reason for it
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Old 07-30-2010, 10:12 PM   #7
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Hardwood over OSB and moisture barrier?


Found this link on here some time ago. http://www.buildingscience.com/documents/insights/bsi-009-new-light-in-crawlspaces?topic=resources/cond-crawlspaces This is what some experts say you should do about a crawlspace. As far as the subfloor material, I like Advantech which is also t&g and the same price as ply. True, the OSB is half the price but is it worth it to save that money now and have to worry about it down the road.
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Old 08-02-2010, 11:04 AM   #8
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Hardwood over OSB and moisture barrier?


Jim, Thanks for the link... a ton of good info to consider. A question, when installing felt do I over lap seams or tap them and if it's tape , what kind?
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Old 08-02-2010, 01:10 PM   #9
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Hardwood over OSB and moisture barrier?


Overlap the seams of felt paper. Use this from H.D.: http://www.fortifiber.com/aquabar_b.html

Don't use OSB, use real plywood. Are you face nailing the wood flooring?

Wood flooring and water do not mix: http://www.woodfloorsonline.com/tech...oodwater1.html

Be safe, Gary

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