3/4" hardwood over 3/4" T&G subfloor

benjamincall

I would like to run my 3/4"x4-5/8" hardwood parallel to the 3/4"x3" T&G subfloor. Should I place a layer of plywood over the subfloor?

Just Bill

yes, but most T&G subfloors I am familiar with run at an angle to joists. A layer of plywood would isolate the subfloor.

Dairylander

What kind of subfloor?

drtbk4ever

The company I am using to install my hardwood suggests that no additional subfloor is needed in this situation if the hardwood runs Perpendicular to the floor joists.

That of course, is dependent on the type/condition of the current subfloor.

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Bill

A DIY Noob that knows just enough to be dangerous.

JazMan

Benjamin,

Installing the hardwood perpendicular to the joists is the normal way to do it. Did you mean to say parallel?

Jaz

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benjamincall

Yes, I understand the flooring should run perpendicular to the joists. My concern is that I heard from someone that hardwood flooring should not be installed parallel to the T&G. The subfloor planks are about 3" in width. I can't have both, since the T&G is perpendicular to the joists (not on the diagonal). Do you see any problem with running the flooring parallel to the subfloor without adding a layer of 1/4" plywood?

benjamincall

3/4" T&G (doug fir?).

The 3/4" T&G is in pretty good shape. It has been hacked here and there for registers and the like, but it seems sound. It has gapping here and there but nothing that seems like a problem.

Gary in WA

I would add the plywood to isolate from the sub floor board's movement with the seasons or any other moisture changes: http://www.woodfloorsonline.com/tech...oodwater1.html Two layers moving at different rates and distances, spells problems.
My 2 cents......
Be safe, Gary

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benjamincall

Gary,

Would 1/4" plywood do the trick? What about fastening?

Gary in WA

Read the new floor manufactures suggestions on fastener length, 1/4" may work. I've put 1/4" plywood on 2x6 car-decking many times. Be sure to use a vapor retarder, not red rosin paper, if over a crawl space or bath, laundry room. This is way better than asphalt coated paper: http://www.fortifiber.com/aquabar_b.html H.D. carries it.
http://www.johnbridge.com/vbulletin/...ad.php?t=58241

http://www.hornerflooring.com/techgu...watervapor.pdf

Be safe, Gary

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benjamincall

Will luaun do the trick?

benjamincall

This is from hardwoodinstaller.com:

There are other older subfloor systems one may encounter and not used anymore. They include:
• 1&1/8" T&G plywood subfloor installed at 90 degrees to 4"x 6" beams spaced 4 feet OC. • 1&1/2" x 5" T&G solid fir deck boards installed at 90 degrees to 4" x 6" beams spaced 4'00" OC. • 1x8 solid fir/pine boards installed at 90 degrees to joists spaced 16" OC. • 1" RED-X T&G particle board subfloor installed at 90 degrees to joists spaced 2'00" OC. • 3/4" or 5/8" particle board found mostly today in modular and mobile homes.

Older subfloors shown above should not be removed but overlaid with 1/2" CDX plywood that is well stapled (2" around perimeter and 6" OC) or glued and nailed/screwed. In all cases, subfloors and underlayments are to be flat to within a 3/16" tolerance in an 8-10 foot radius.


The "older subfloor" that is closest to mine is the 1x8 solid fir/pine at 90 degrees to the joists. Mine is 1"x4" (3/4" by 3.5" true dimension) T&G. Apparently I need to put down 1/2" CDX plywood. I notice the Home Depot says the luaun it sells is "moisture resistant" and is suited to high humidity areas: http://www.homedepot.com/Building-Ma...atalogId=10053

benjamincall

Here's a site that recommends 3/8" or 1/2" CDX glued and screwed to the plank subfloor.

http://www.hoskinghardwood.com/Hardw...ub_floors.aspx

On this forum, I've read that you want to use narrow crown staples and no glue. Does any one have conclusive evidence from the industry pointing to one method over the other?

Here's one more:

http://www.thefloorpro.com/community...erlayment.html

Gary in WA

The luaun doesn't have the layers required for nail withdraw resistance, for me. http://www.apa-europe.org/Languages/.../PDF/R340G.pdf

Be safe, Gary

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benjamincall

That reference was awesome!

Here is what I gleaned from the article (editorial notes in red):

1. Use a minimum plywood thickness of 3/8" "over lumber or uneven surfaces." I believe this standard applies to to the T&G planks.

2. "Space [underlayment] fasteners so they do not penetrate framing."

3. Avoid the use of construction adhesive because it can create installation and appearance problems for "certain types of resilient sheet flooring products." I'm installing hardwood, but I believe that advice indicates that I won't need to glue the underlayment.

4. Use 3d ring-shank or screw-shank nails that are a minimum of 12-1/2 gauge in diamter. Wouldn't my 1/4" crown stapler do the same job? Since I'm using 3/8" CBX, would I go with staples that have a 1-1/8" leg to avoid pentrating the framing members?

5. Fasten panels 3/8" from their edges.

6. Fasten panels every 6 inches along the edges.

7. Place fasteners in an 8-inch grid in the field (eight inches north-south and east-west).


I've read all sorts of conflicting recommendations on the Web, so the above recommendations seem to be points of confusion. The APA is a source I trust, so I'll stick to this information. Please let me know if I've misinterpreted. Thanks, Gary!