Underlayment over Advantech?

Old 01-25-11, 10:12 AM
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Underlayment over Advantech?

I have a 20'x20' area on the second floor of my new addition that I intend to cover with carpeting. The subfloor is 3/4" advantech T&G glued & nailed (ring shank) to
10" joists spaced 16" oc. Will I need to install a plywood underlayment or is this considered solid enough as is? The joist span is 12' max. The floor feels very solid already. The space will be used as a bedroom/hallway.

thanks for your opinions
Old 01-26-11, 04:24 AM
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Welcome to the forums! Sorry for the delayed response. It is customary to apply another 1/2" plywood at opposite grains to the Advantech prior to installing flooring, whether it be tile underlayment or wood. How does your floor match up to the remainder of the house. I would suspect it is a little lower than the remainder. If so, apply the additional 1/2" then put down the carpeting. IF it matches, then carpeting would be no problem. If you ever decide to pull the carpeting and install hardwood, you may want to add more stability to the floor, so provided you have the space, you can do it now. You didn't specify the size of your floor joisting, as that will have some effect on what you should do.
Old 02-22-11, 06:33 AM
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If the rooms to get just carpet any thickness underlayment that's subfloor rated, that gets all the floors even will work.
The problum I see is with Advantec it's made so there's a gap at the seams to allow for expantion. There going to show through the carpet.
Over time those nails are going to work loose once the wood drys out. I'd add a ton of 3" long ceramic coated deck screws. Look over some of the other post where there now stuck with removing the carpeting to get to the sub floors to now add screws.
Any under layment never gets attached into the joist and the seams below should never line up with the underlayment.
Underlayment rated means it will have ext. glue and no voids in the cores.
What your trying to do is pull down the underlayment tight to the subfloor where there is always a tiny gap between the joist.

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