Nailed-down flooring question

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Topic by tbone posted 02-16-2011 07:28 PM 3364 views 0 times favorited 7 replies Add to Favorites Watch
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3 posts in 5035 days

02-16-2011 07:28 PM

Don’t tell anybody I’m over here, but I just sneaked out from Lumberjocks. There’s a discussion over there about why there is such a large expansion gap recommended for nailed-down hardwood flooring. We all understand the concept of wood movement, but 3/4” seems way too much. If all of the planks are nailed down, then the general thinking is that the only plank to be concerned with is the one on the outer perimeter.

Can any flooring experts here tell us why that is wrong? ...or right?


View rrdesigns's profile


100 posts in 4642 days

02-17-2011 06:02 PM

You do need a gap for expansion, but that gap is usually limited to slightly less than the thickness of your baseboards. I have not nailed down hardwood floors although I have refinished them. I do, however, install floating laminate floors and a 3/8” to 1/2” gap works well for those.

-- Beth, Oklahoma, Rambling Road Designs

View CessnaPilotBarry's profile


5 posts in 4544 days

02-17-2011 10:15 PM


I’m on LJ’s but I missed that thread. Once upon a time, I put in a lot of hardwood flooring.

Manufactured raw hardwood flooring has a built-in gap, except for the top. If you put two pieces together, you’ll notice that the only contact is the edge of the show surface, the tounge and groove and bottom sections are relieved. You’d also notice this if you tried to edge glue flooring into a panel. As you tighten the clamps, the face will bow outward.

The edge gap is to allow the entire floor to expand and not bow. As an example, red oak can move 1/16”-1/8” PER FOOT in width. In theory, if you installed very dry flooring at the dryest time of the year, you could easily eat 3/4” per edge in a decent sized room during a humid summer.

Since the nailed boards have a bit of give, the expansion should distribute itself, then the following contraction should allow only very thin cracks to open up between boards. This is also why the planks aren’t glued.

In a perfect world, the original expansion will be perfectly distributed, then exactly taken up, then perfectly distributed again. The world isn’t perfect, so as the wood acclimates and moves back and forth over the years, some rows may end up with larger gaps than others.

On a related note, the back of the floorboards are milled to prevent the board faces from cupping. Breaking up the back surface prevents it from swelling as a whole face and cupping the other face. Concave (cupped) boards create mismatched edges and visible problems, convex boards are much harder to see and trip over.

View allmyfingers's profile


31 posts in 4179 days

02-27-2011 05:10 AM

we use a 1/4” gap on all floor installs

-- caring costs nothing

View Todd Thomas's profile

Todd Thomas

735 posts in 4979 days

02-27-2011 03:17 PM

we install some floors both finished and unfinished and I’m with Beth on this. We try to keep slightly under or baseboard measurement. This way the base covers incase we don’t use a toe mold….....plus it all cover your idea, my idea, their idea of a 1/2 inch when installing.

-- Todd- Oak Ridge, TN

View sillvan's profile


3 posts in 2171 days

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