Newbie Hardwood Underlayment Questions

Old 11-09-08, 08:35 AM
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Newbie Hardwood Underlayment Questions

Hi. Thanks for helping me to cure my ignorance about installing hardwood flooring. I have a few very novice questions.

I have carpeting in my living room that I am going to replace with prefinished bamboo flooring. I am choosing my materials and contractor now, and I want to have a complete understanding of the options and the work involved.

The carpet is tacked and is sitting on top of what appears to be 1/2" plywood. This appears to be the subfloor, but it it possible that it is a second layer of plywood on top of the plywood subfloor.

I have been reading about the various underlayment options, and I am confused about whether the underlayment is supposed to include a second layer of (good) plywood on top of the subfloor. I am planning to put 15lbs builders' felt directly underneath the bamboo.

So, my questions:
Do I need both the plywood and the felt for the underlayment?
Is this any different if my subfloor is 3/4" plywood rather than 1/2"?
Given that I have carpet (in a home constructed in 1980), is it likely that the tacks are attached directly to the subfloor, or to an underlayment layer on top of it?

Thank you for your help!
Old 11-09-08, 09:03 AM
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Odds are you subfloor is 1/2" or 5/8" plywood nailed directly to the joists. You can check it yourself by looking down the side of a furnace vent if any come up thru the floor, or even drilling a small hole -- say 3/4" thru the subfloor and measuring the thickness. Your carpet is likely attached directly to the 1/2 or 5/* subfloor with tack strips. Regardless of the thickness what you need to do is:
1. with a screw gun screw the subfloor to the joists every 6"-- this will reduce the possibility of floor squeaks
2, the need for the moisture barrier (felt) is dependent on your site conditions and the probability of moisture. If you're over a basemrnt this would be overkill. If you're over a crawl space with high moisture content (not a good situation on its own) then maybe. Chances are its overkill.
3. the need for additional underlayment is again dependent on your site conditions. How firm is the subfloor? WHat condition is it in? How smooth is it? In a 1980's house chances are additional underlayment under 3/4" bamboo flooring is overkill.

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