So, I put an expansion onto an old cabin that I worked to get back to structural soundness a few years ago. It's what I could afford and I didnt mind doing the work.

Im not a carpenter, more of a wood butcher.

I've kinda dreamt of having hardwood floors, well my whole life. So I figured with this expansion it was the time.

The area though has large humidity swings. During the winter it gets fairly dry to the point you are shocking yourself on doorknobs, and during the summer it literally feels like we are laying down on wet pillows/blankets.

The room I want to lay wood flooring is 24x26 and it's fairly open sans a corner partitioned area and foyer area.

This sits over a crawlspace, and is near a pond and two creeks. So moisture IS a problem. When I paneled this room with 7/8" natural poplar, I have many boards that I can pound back against the wall a 1/8" because they expanded and lifted against the wall. When I did the ceiling this winter I was smart enough to leave much larger expansion gaps and much longer nails at an angle.

Now Im at the point that I want to install hardwood floors, and found quarter and rift sawn white oak 4" T/G unfinished White Oak for $6, which in my area is good. I picked this because I had been told that it does not expand/contract side to side like plain sawn does, instead if expands/contracts from top to bottom if that makes sense.

Well I did a little digging and while it doesnt expand/contract like plain sawn, it sure does expand side to side, just half as much.

If I use the formula they have online: I have a difference of 6-7% MC in my wood paneling so it probably would be the same for my flooring if not worse. If I multiple 7x the width of the board I get 28 x .0018 = .0504 per piece. If I take 24' x 12" I get 288 inches, I then divide 288 to the width of my board 4" and get 72 pieces which results in 3.62 inches!

Surely before dehumidification, wood flooring was a thing how then do people put down hardwood flooring? I expand the building will also expand and contract as well, but when I put a smaller gap in my paneling with that reasoning I obviously learned that my paneling expands/contracts much quicker than the building. I even popped window molding etc and had to rip pieces to allow for expansion.

So Im not sure what to take away here for wood flooring. Am I stuck with stone then?

I do plan to add some crawlspace dehumidification but the old building is leaky at best, and I would need some serious commericial dehumidification to really make any difference in this place, but something will be better than what we have now.

SO the question is, will my hardwood , even though it is quarter and rift sawn white oak, expand 3.6+ inches in a 24' span?

Thanks all, hopefully you can help me keep my dream alive with some logic here, or keep me from making an expensive mistake.

I should add I was planning on running the hardwood wall to wall with a 3/4" gap, however I will have heavy kitchen cabinety and an island sitting on top, or would it be more wise to put ply underneath and run hardwood up to the ply with a gap there as well?

Yess you can get that much expansion. With a plan to spread that much expansion over the whole floor, use washers between rows of flooring to give the wood places to swell into during the "damp" season. An eighth inch thick washer every two feet may look funny and you lay the floor, but the gap will disappear as the wood gets acclimated, depending on the moisture content when the flooring is laid.

Rift and quartered won't expand and contract like a flat/plain sawn, due to the way it's cut from the log. The movement takes place somewhere in the are of 30-90% vertically.