I see information like this a lot:

http://www.lacrosseflooring.com/news/lu ... ns-popular

"Because White Oak is quartersawn, it is a more stable flooring product than plain sawn lumber. It will naturally shrink and expand in its thickness, not width, so the floor remains more stable with fewer cracks showing between the boards in low humidity periods."

I have rift/quartered white oak ready for install. Indoor humidity is 33% and it's been acclimating for 2-1/2 weeks. Chicago region. Should I put a small gap (dime size) between every 8th row or so? Or will the wood not expand too much in the summer? coefficient of expansion of white oak is 0.00365

5in width with a 2% moisture content swing equates to (5*2*.00365) = 0.035" per row. 10 rows is almost 3/8ths of an inch.

So with the boards nailed, etc, how does wood flooring really move like this? My parents had white oak in a home that was run lengthwise and the width of the room was 40 feet. They never had problems for years and years and we didn't know any of this stuff. Installed ourselves in the wintertime. That floor was plainsawn. So across 40 feet that is 4inches of expansion per the official numbers. At the time we left 1/4in room for expansion at the wall. So the floor should have buckled under the pressure.

According to the manufacturer of my flooring, generally, only the last couple of outside rows expand, not the whole floor. The expansion is usually in the direction of the tongue. Think about how you figured it above. If that were the case, then even the standard recommended 3/4" allowance for expansion wouldn't be enough for nearly any sized room larger than a small bedroom.

FYI: wood expands most across the grain, and very little length ways. Thus, quarter sawn flooring would expand less than flooring cut across the grain.

"Think about how you figured it above. If that were the case, then even the standard recommended 3/4" allowance for expansion wouldn't be enough for nearly any sized room larger than a small bedroom."

Well that was my point. But I think as you say those figures cannot possibly be for each board in a floor, or the expansion gap would have to be huge.

I am going to get my RH close to 40% and install.