I just finished installing some prefinished solid hardwood flooring in my bedroom. The instructions had me leave a 3/4" gap between the flooring and the walls, which I dutifully did. this gap is supposed to be for "expansion due to changes in humidity."
What I can't figure out is how the heck this flooring could possibly expand. Now I understand that wood expands and contracts with changes in humidity, although primarily across the grain (with the grain hardly changes at all). The problem I see is that every single piece was nailed down to the subfloor, so if it is going to expand that much, isn't it going to pull out or atleast bend all the nails?
(background: floor was installed on the second story over a 3/4" chip-board subfloor. Room was approx 15'x20')
3/4" is a pretty big gap, but if it's recommended by the manufacturer, then it's probably right. I've installed Engineered Flooring and Hardwood, but in both cases, the warning is more for with grain expansion not across grain. In my case, it was 1/2" gap with maximum length of 24 feet with expansion joint in between.
Oh.... it will move alright!
I have seen wood floor stand at attention without proper expansion.
The wider the plank the greater the expansion. you must have put in a wide plank if it called for 3/4 the norm is 1/4-1/2 most guys are lucky to put 1/4 and that is because the builder is to cheap to put down 3/4 rd and they want a small 1/4 shoe mold.I have even had customer complain about the size of 3/4rd "It''s to big" I say "It's to bad" (not really).
It will expand and shrink enough to break nails that is why they sell those big big 14-12g staples. I use cleat, a steel cleat, a Powernailer cleat!
It will move like a chest when you breathe, all at once, each board impacts the other each board expands at the same rate.