vapor barrier placement and underlayment?

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Old 07-15-08, 10:36 AM
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vapor barrier placement and underlayment?

I have a split level home where the bottom floor is below grade. I will be installing an engineered hardwood floor on that bottom level. I currently have 3/4" OSB subfloor over 24" OC I-joists. I plan to add another 1/2" of OSB to that subfloor before installing the eng hardwood floor.

My question is where is the best place to put the vapor barrier. Options:
A) Insert vapor barrier between the existing 3/4" OSB and the new 1/2" OSB and also insert a vapor barrier between the 1/2" OSB and the eng floor. This seems a bit overkill but one of the installers who gave me a quote recommended this. I'm kinda worried that if mositure were to somehow get in between those layers of vapor barrier that it would be trapped.

B) only insert vapor barrier between the existing 3/4" OSB and the new 1/2" OSB. This seems like a good idea because it would protect the ends of the new 1/2" OSB from possible swelling if moisture develops unders the home; however, if I did this I would not be able to glue down the 1/2" OSB to the 3/4"...I would be left just screwing it down.

or
C) only insert vapor barrier between the new 1/2" OSB and the eng hardwood floor. Of course, the installer is planning to staple down the eng hardwood floor so I don't know exactly how effective a vapor barrier is when popped with a bunch of staples.


Also, one installer recommends I use one of those combo foam paddings that is close to 1/8" thick under the eng hardwood floor. The eng. hardwood floor is 1/2" thick and he plans on stapling the eng. hardwood floor down. It seems a bit strange to me to use a foam padding under a eng. hardwood floor that will be stapled down....that layer of foam seems like it would not be good for the staples if the wood can have movement in it.


Thanks for any possible help/suggestions!
Matt
 
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Old 07-16-08, 12:42 PM
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Matt -

Read my post on one of the below questions that talks about OSB.

You want to install 1/2" Advantech (sealed subflooring) *square edge - not tung and groove. Now, because your Floor Joists are 24" on center and not 16" on center, you will want to run your new subflooring in the OPPOSITE direction of the 3/4" current OSB Subfloor!

Each sheet of Advantech Subflooring you will want to glue down using an adhesive (Caulking Gun Tube Style) called PL-250 or its' equivalent. Apply it in squiggly lines 2" from the edge right to the other side, but keep any adhesive at least 2" from the edge, you want the next sheet to fit tight up against the previous sheet - so you don't want this stuff squishing out all over the place! Lay the sheet down walk on it, then lift it 6-8 inches up off the subfloor (osb one) and then put it back down... do this 3-4 times and this will activate the adhesive and your sheets will definetly not SQUEAK! Then SCREW down each section of new subflooring using the nailing pattern (small + signs on the Advantech sheets).

Once you are done laying the new Advantech subfloor, lay the blue foam (if you have moisture problem you may want to lay down a layer of 15# felt paper first (in the direction of the flooring) (overlapping each row by 6"). If you use the 15# felt paper (AKA "tar paper" (and I usually recommend it anyways), then install the blue foam. It will cushion the flooring under your feet and will actually help with sqeaking.

Follow the manufactures specifications for nailing down the floor, in fact most engineered floor manufactures REQUIRE the Blue Foam under the flooring and they will give you specification on how to install this foam. DO NOT OVERLAP THE EDGES OF THE BLUE FOAM! TAPE THEM WITH NO OVERLAP!!

Good luck,

Greg - Retired Hardwood Floor Install/Finisher Owner
Maine
 
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Old 07-16-08, 05:24 PM
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Thanks Greg...excellent suggestion however the installer has already purchased and delivered the 1/2" OSB. I actually got qutoes from 3 different installers and they all said they would just put 1/2" OSB on top of the existing 3/4" OSB. I wish I would have researched this Advantech product before giving them the go ahead.
 
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Old 07-17-08, 09:52 AM
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I would ask them to take it back in get the Advantech subflooring, it will cost a bit more per sheet but it will give you a protection against the money you are well spending. I have seen OSB subfloors fail horribly in high moisture situations and have had to rip out what OTHER floor companies with less experience have installed.

Remember that you have floor joists that spaced 24" OC, that is not a good thing and the adventech will strenghten up your entire floor system so much better than the OSB!

Just my professional opinion. Oriented Strand Board (aka OSB) is accepted by the National Wood Flooring Association and the National Oak Flooring Manufacture's Association... but, only in Floor Joist Spans of equal to or less than 19.2 inches!! See this link for more info.

Note the remarks in the OSB guide link about Crawl Spaces and moisture!!!! **NO GOOD

Greg - Retired Hardwood Floor Installer/Finisher
Maine
 
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