# Hardwood Parallel Over Shiplap Subfloor?



## seattlealex (Dec 17, 2009)

Hello floor pros.

My wife and I bought a house that was built in 1961 and has some real nice shag carpet in a few rooms. Gotta love that shag! We plan on having a new wood floor professionally installed, however I will be doing all the prep work with the subfloor.

Our plan is to rip out the carpet and install 3/4" hardwood (3 1/2"). Both of the rooms getting the hardwood are next to the hall, which has a slate floor. We'd like to install the new wood floor to be level with the slate.

The slate is 1/2" higher than the current subfloor under the carpet. The subfloor is 1"x8" shiplap installed diagonally over 2x10 joists and then a layer of 3/8" plywood over the shiplap. 

I'd rather not rip everything out and install new plywood, but I will if that's what it takes.

I'm also willing to install blocking between the joists, so I can run the new floor parallel to the joist. (would this be a glue & screw?)

I've read a bit online from nofma and from what I read they say installing over the 3/4" shiplap would be okay if it's flat and property nailed down. nofma also say "hardwood should be installed perpendicular to joists", which I read it to say it doesn't have to be.

I will need to install some thin plywood on the shiplap to bring it up to the level we want (1/8" or 1/4") not sure yet. Any suggestions on best product to do this?

I have good access under the floor, so blocking the joists, or caulking the shiplap (if needed) is very doable.

Any thoughts on transition from slate to wood?

Any advice would be appreciated. Thank You. :notworthy


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## PrecisionFloors (Jan 24, 2006)

If it were mine, and the existing 3/8 is in good shape, I would install 1/4 Birch underlayment (look for Halex, Multiply, or Powerhold) run it opposite direction to existing. Install with a narrow crown 3/4" staples. Then you can run the hard wood any direction you want. I doubt you need any blocking but I'm not there....when in doubt, overkill is consistently more fun 
What is the current edge like on the slate? Will the wood be running parralel or perpendicular to it? Is it straight?


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## seattlealex (Dec 17, 2009)

Thanks for the reply.

I guess my description of the job wasn't very clear. In order to get the new wood floor level with the existing slate I'll have to remove the 3/8" plywood which is on top of the shiplap. then I'll have to install some 1/8" plywood or underlayment, so the new 3/4" hardwood is level with the slate. Maybe we just need a few layers of 30 pound tar paper to bring it up. What do you think?

Any thoughts on installing the flooring parallel to the joists?

The slate floor is broken flag stone, so the edge next to the hardwood is a bit rough. I'm assuming that we'll need to put in a strip of morter to even it out.

I've attached a drawing of the job to make it a little more clear.

Thanks, Alex


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## astor (Dec 19, 2008)

*Better diagonal*

What is the distance between joists?12" or less?
The best solution to this is installing the wood floor diagonal opposite direction of the the subfloor.I would not install another 1/8".The high difference will be only 1/8" between slate and the wood which is not noticeable once you apply grout between.Or gradually rise up in that section with shims/or ply.
If you install the wood parallel to the joists you take a some chance of getting gaps,squeaks and in long term waving problems.
Carefully examine the subfloor for any sagging between the joists,let a heavy person stand and see if there is a movement when stepped out.


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## seattlealex (Dec 17, 2009)

The joists are on 16" centers and 16 1/2 feet long. I just read the install instructions from NWFA and it said installing solid wood parallel was acceptable if cross bracing is installed between joists. They don't specify the technique or number needed, however another site said to install cross bracing in the middle of the joist span or every 8 feet, whichever is shortest.

The NWFA document also stated it's acceptable to install hardwood over solid subfloor planks, but they specify 1x6 installed diagonally. The wood I have is 1x8 diagonally installed. I'm not sure if this is a problem or not. I think I'll just have the installer come over and look at it. 

Thanks


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