Wood flooring newb in need of guidance. 1957 CA ranch style home on raised foundation with existing oak flooring and a 4 month old , 150sq ft living room extension on concrete slab at same elevation(approx. 1/8" under) as existing oak flooring. Would like new wood flooring over entire living room space(550sq ft old + 150 sq ft new), but unsure what to use in this situation. Do I need a 3/4" plywood base screwed and glued first, can I just use a vapor barrier over the concrete and use engineered over the entire space, should it be nailed,floated, glued and any of the above combinations of solutions. Help! The HD's and Lowe's have been less than worthless in my search for answers.

I can only assume, it is an engineered cross-ply oak, glued down directly to the concrete.

Careful of new concrete. It has a lot of moisture vapor emissions.

Are you saying I should use an "engineered cross-ply oak" given my situation? Would I be gluing down the entire floor, even over the existing oak flooring, or would I nail where possible and glue over the concrete?
Thanks

I assumed wrong


The existing hardwood... What thickness is it? Is it a solid or engineered?


Raised foundation? As in peer & beam?

Sorry for the lack of sufficient info. Its a pier and beam raised foundation with sufficient crawl space to manuver around. The existing wood floor is the original 3/4"(?, I think)thick x 2" wide solid oak floor from 1957. I've taken many crawls under the house for various projects and noticed that the pier/beam intersection had been shimmed in a couple places. Is this normal, is there a better way, and/or should I tie the beams together with 2 x 8's spaced every ? to help reinforce/strengthen the floor.

Thanks again for the response Floorguy!

I have worked in similar conditions in jersey. I have good luck with putting in 3/4 plywood with the Remington nailers. Then 15# felt paper, and then a 3/4" solid floor. This process will eliminate any moister issues with the concrete, and you should not need to crawl around to tie joists together. Some subfloor glue under the ply never hurts either. Good luck

Sorry for the need for clarification, but your saying I can lay down 3/4" plywood(after applying the 15# felt) over the entire area(existing wood floor and concrete extension), nail the plywood to the existing wood floor(and glue it to the felt , which is glued to the concrete?) and nail the new 3/4" wood floor over the entire area? Being unfamiliar with flooring nailers, will the 3/4" plywood thickness provide a thick enough substrate over the concrete or will the nails "bottom-out", bend, etc if they penetrate beyond the plywood thickness?

Thanks for your response.

Interesting. I am trying to follow but what you said "150sq ft living room extension on concrete slab at same elevation(approx. 1/8" under) as existing oak flooring."

Does this mean the new concrete is 1/8th inch below the top of the old wood flooring or 1/8 inch below the bottom of the old wood?

Sorry, will clarify. Try to feather out hight difference from the existing wood to the concrete with 30# felt. This is done by stacking several sheets of the felt paper and overlapping(like a deck of cards--stack it up--and then slide them out--get the idea?)then glue and nail the plywood. and then the 15# felt(no need to glue, just roll it out), then nail the new floor. Yes the 3/4 nailer will work fine if you use 1 1/2 fasteners, not 2"

How about screwing the plywood down instead of nailing it.

Can anyone address what to do before you just "nail down" plywood to concrete for the fella? I mean lets be specific here artisian. No skippy the steps!

What about addressing going from concrete to wood. Would we possibly get some panelization here from the wood moving in difference to the concrete slab?

1/8" is not going to effect the ¾" plywood, as you go from one to the next.



I would float the subfloor over a moisture retarder and fasten the finish flooring, to it. I would not puncture the moisture retarder, by fastening down the plywood, unless I have spread asphalt roofing mastic, to set the moisture retarder into.


What good is a moisture retarder if you puncture it everywhere?

The concrete still needs to have MVE tests to determine if it is acceptable.

Floating subfloor!

Wow!

true, if you feel the need to float, I've never been a fan though have done for the occaisional client. If a moisture ckeck is done to the concrete, and it is in the green, would you not be safe with the felt on top. I just think the floor has that nice tight feel when everything is fastened. Have you ever had moisture problems in this house, if not you would need a good amount of water(a flood) to ruin the floor--which homeowners would cover.

With a floating subfloor, you don't lay 4x8 sheets. You cut the plywood into 2x8 planks and stagger them, randomly, across the floor.


If the concrete tests OK today, does that mean it will be OK next week, after the rains we had everyday since your test?

Is concrete MVE static, or is it dynamic?

Is your 15# felt going to surpress MVE, all by itself?

Seen many wood floor cupped and buckle, and it had 15# felt over the plywood and poly plastic under the fastened plywood over the concrete. One had been installed for 9 years before they had enough rains to cause a problem.

Then explain why you would float a subfloor with a plastic retarder instead of the wright way with mastic and plastic, fastened?

Maybe the floor with 15lb felt had nothing to protect it like poly over the dirt or the poly fastened without mastic and layered.

I am just trying to learn from the WFMA expert here. I is just a poor ole installer out west. Things are different out here. Everything shrinks. I would hesitate to float a subfloor here. Actually I would refuse.