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Old 04-22-2008, 08:16 PM   #1
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Underlayment height for tile / carpet....

My current subfloor is in terrible condition: dozens of soft spots throughout the house and EVERY step we take, the floor squeaks and creaks. There is no underlayment at all.

Along with a new subfloor, I will be putting down an underlayment prior for new tile and carpet. Initially, I was simply going to put down another 3/4" underlayment for both the tile and carpet, but am now reconsidering.

With a level underlayment throughout, once I put down the cement board and tile...will that be too high for a nice transition with the adjoining carpet, which will go down directly on the plywood underlayment?

How about a 1/2" underlayment for the tile, to "lower" it a bit in relation to the adjoining carpet?

I am confident in doing this project. Permit pulled, just bought a toe-kick saw to remove the old subfloor. Will glue / screw the new one in...but any words of wisdom are welcome.

What type of plywood is recommended for the above?

Thanks in advance!!!

Is a 3/4" subfloor + 1/2" underlayment + cement board structurally acceptable? (I would think so, since there is only a 3/4" subfloor in place right now, which I think is very marginal!)
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Old 04-22-2008, 09:13 PM   #2
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When properly fastened, 3/4" plywood subfloor with joists at 16" o.c. and joists not overspanned, should give you a good subfloor. Adding another layer of plywood of course is always a good idea, the more the better. You should be fine with 1/2" underlayment. You decide the levels you want and whether to go thicker in the carpeted areas.

Rather than 1/2" backer board under the tiles, you can use 1/4" or even better Ditra membrane which adds only 1/8".

Subfloor is 3/4" t&g exposure 1, nailed and glued to the joists. Underlayment is square edge B/C grade spaced 1/8" and fastened only to the subfloor, not the joists, no glue for the underlayment.

Let me know the type, size, spacing, species, grade and unsupported span of the joists. We always start with the framing.

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Old 04-23-2008, 12:12 AM   #3
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Thanks, Jazman!

I have 10' span 2x8's...16" o.c. Grade, type and species are unknown, sorry. Joists and framing appear solid & in great shape. Unknown why the subfloor throughout the home is in such sad shape...dry climate, no water damage...

Subfloor: Should I trim the T&G edge (make it a square edge) where it will butt up against the wall? Do I butt it up firm against the wall, or leave a 1/8" space?

I plan on blocking the joists around the wall perimeter for extra support.

What type glue / screws do you recommend for this project?

Thanks again, this forum rocks!

Last edited by scheenstra; 04-23-2008 at 12:16 AM.
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