Wood Movement in Flooring

[Warren Wilson]

I am installing an "engineered" wooden floor over the plywood subfloor in my bedroom. The "engineered" material is essentially a nice plywood with a tough face. (By "nice"plywood I mean 8 plys in the half-inch-thick product with no voids).

So I am installing plywood over plywood and nailing it in place (nails at 4" - 6" intervals).

Here is my question: why does the manufacturer recommend a 1/2" expansion space around the perimeter of the flooring? It's plywood. It's nailed to plywood. The walls are built on the subfloor and everything is fastened to the floor joists.

I will, of course, follow the manufacturer's recommendations. But this slightly violates my sense of wood movement. (Even on the issue of the solid wood oak floor I installed elsewhere in the house, I am slightly puzzled, as it is very securely nailed to the subfloor throughout. This would seem to seriously inhibit independent movement of the subfloor and flooring, and with all those nails would wood expansion and contraction not create cracking and buckling instead of growth at the edge?)

[Erik Loza]

I sell engineered flooring. To answer your question, the reason is because once all the boards are glued together, they essentially expand and contract as one solid piece of plywood. From the center, out, unlike solid flooring, where each board will expand and contract independently. The fact that it has a plywood substrate is what mitigates any potential cupping or warping. I agree that it seems counter-intuitive if you're nailing it down (though it's often just glued down) but that is how it works. Also, the better quality the flooring (the plywood substrate), the less movement you will have. Hope this helps.

Erik

[Pat Barry]

I am installing an "engineered" wooden floor over the plywood subfloor in my bedroom. The "engineered" material is essentially a nice plywood with a tough face. (By "nice"plywood I mean 8 plys in the half-inch-thick product with no voids).

So I am installing plywood over plywood and nailing it in place (nails at 4" - 6" intervals).

Here is my question: why does the manufacturer recommend a 1/2" expansion space around the perimeter of the flooring? It's plywood. It's nailed to plywood. The walls are built on the subfloor and everything is fastened to the floor joists.

I will, of course, follow the manufacturer's recommendations. But this slightly violates my sense of wood movement. (Even on the issue of the solid wood oak floor I installed elsewhere in the house, I am slightly puzzled, as it is very securely nailed to the subfloor throughout. This would seem to seriously inhibit independent movement of the subfloor and flooring, and with all those nails would wood expansion and contraction not create cracking and buckling instead of growth at the edge?)
I think that the manufacturers instructions for the 1/2" gap on the perimeter is based on a floating floor install. If you are nailing it down, then it doesn't seem to make sense. Are you sure about the install instructions?

[Wayne Lomman]

It's not just a wood issue. Houses move over time. You have to allow tolerance for this movement. If you build a house to furniture precision it will destroy itself over time. Cheers