Adequate sub floor for hardwood?

Hello-

I have a contractor building a porch to the house, it will be raised off ground from 6"(next house) to 20" (porch outer wall) setting on Big Foot concrete filled pillars. Floor joists 2x12, 16" OC. 2x6 outer walls. I want to install 3/4" solid prefinished hardwood flooring either 2.25 or 3" width at variable lengths.

The contractor wants to lay 1/2" 4x8 plywood on top of joists then 2(stacked) - 4x8x2" foam (closed cell, non compressible) blue board for a total of 4" depth @ R value of 10. Then on top of the blue board 3/4" tongue & groove plywood. Total subfloor depth is a sandwiched 5.25". Is this acceptable for a hardwood floor subfloor? The blue board is said to act as a vapor barrier also, although I will have poly & recommended under layment under the hardwood flooring installation, question is, is the blue board O.K here?

Thanks, Robes-

 

Just to be clear, the contractor wants to install the wood flooring on top of the foam?

What type of floor, floating, glue down, nail down?

 

Hi Marq1-

The floor will be nailed down 3/4" solid prefinished. So, from the top down in order it will be: 1) 3/4" hardwood. 2) manufacturer recommended under layment. 3) 4 mil poly vapor barrier. 4) 3/4" tongue & groove plywood. 5) 2" blue board. 6) 2" blue board glued to #5 above. 6) 1/2" plywood.7) all above resting on top of 2x12's on 16" centers.

 

Honestly, I've done a lot of floors but never came across this configuration.

Typ the nail down flooring is on top of the sub floor (with underlayment) so nails can penetrate the sub floor and joists.

I would have concern that the flooring would not be securely attached to the floor with that layer of foam. The additions that I have seen had all the foam/insulation between the joists!

 

Are you sure you understand his method? Because I think you don't understand what he is going to do.

Generally you would drop 1/2" plywood in BETWEEN the joists (rests on top of 1X2 cleats) then you drop the insulation BETWEEN the joists. The 3/4" plywood goes right on the joists. Not 4 1/2" above them.

From a nailing standpoint, the only thing that matters is the top layer of 3/4" subfloor, which- if it's glued and screwed to the joists- is adequate.

 

5/8" plywood is minimum for nail down hardwood. 3/4" minimum if using OSB. As others have stated, it is the final layer of subfloor that matters. I Use 15# felt paper under the hardwood as a sound deadener and vapor barrier. Eliminate the poly as it is not needed.

Wouldn't batt insulation between the joists suffice without this complicated sandwich you are putting together?

 

XSleeper-

Talked with contractor and he corrected me as follows. He will seal all joists with a hand painted on deck sealer. There will not be anything between the joists. 1st layer on top of joist will be 1'2" ply glued down, next layer (on top of 1/2" is the 2" blue board glued to 1/2" ply. On top of blue board goes 3/4" T & G CDX + glue. This 3.25" sandwich is then screwed down with 4" screws. This is the subfloor he insists is the way to go. He says the blue board is closed cell foam, non compressible and also is a vapor barrier.

I insisted changing out his 3/4" OSB (Gold; suppose to be made for/as subfloor for hardwood using sealers & waxes) "chip board" to 3/4" CDX T & G, he's fine with doing that. He also said he'll run this buy his flooring "go to" guy to get his opinion. The contractor is also telling me to go with staples over nails for my 3/4" Hickory.

 

As long as he follows a good screw pattern, it sounds fine to me. (Since its not 4" of foam like you originally said). The plywood is a good call.