My husband and our contractor friend are installing our hardwood this weekend. They were supposed to undercut the drywall so we could leave a 3/4" gap on all sides. However, in their infinite wisdom (and my absence) they did not do that and only left 1/4" on all sides Neither one believes a 3/4" gap is necessary. The instructions for the hardwood state minimum of 1/2", larger for larger rooms.

It's a 3/4" solid patagonian rosewood floor, stapled, going over a 9' basement. The good news is, we can always undercut the drywall after the fact too. The living room is 13' wide and 24' long, with the wood going the length of the room (so the major expansion will be over the 13' width). The bedroom is 15' by 16', and then a 3' wide hallway.

How exactly does wood move when it's stapled anyway? If I can explain that to them, maybe they'll believe me

So, who is right? And how important is it that I make them go back and undercut the drywall?

It is true one can go back and undercut at any time, but after you make the cut how are can you remove the cut portion? You can't without removing a starter row or last row.

For rooms of your size I would just leave it for now, or, go ahead and make the cut and let the cut portion fall down in the gully, that will offer about an 1/8" more because Sheetrock sticks out a little from studs anyway. Manufacturers use a rule that the expansion should equal the thickness of a board. You do not need 3/4" expansion in a normal residence.... now large gym floors, ect. would be a different story.

As long as the house is acclimated and the flooring matches, and the house stays at those conditions, the flooring won't move. If you do have high moisture that does cause some floor expansion, it will only move toward the wall the tongue is facing so that would be the only wall that might need to be cut. Sheetrock crumbles pretty easily so more then likely you wouldn't need it to be cut out.

The rule of thumb is 1/4" per 12' of flooring for expansion. Some woods and products are more/less stable then others so that can change a bit and on very large areas you can use washer spacer in the flooring as you install to allow for expansion like in gym floors. 100' across.

If your solid flooring expands enough to push into the wall and start to buckle more then likely you have major water leak some where and it's time to call your insurance agent. Wouldn't matter if you had 1" for expansion or 1/4", if the flooring expands that much it's pulling the fastners loose and it's time to tear out and replace.

Perhaps they felt that undercutting the drywall is unnecessary because the baseboard and shoe molding combination would provide plenty of space for a gap? Of course, if you installed the hardwood butted against the drywall, then such an expansion gap is impossible to achieve without undercutting.

Regardless of the answers folks give you, refer to the hardwood installation instructions for the specification--your warranty depends on it!