Can cupping be caused by too small an expansion gap?

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Q: I have a wood floor that has been cupping since installation. The installer argues that we have moisture issues and we do show high moisture ratings. However, when we take up the baseboards the wood floors have been installed up to or within 1/8 inch of the drywall. I know wood needs space to expand but I am unsure as to what size expansion gap for hardwood flooring is appropriate.

Most significantly, can wood expand in width and in length? If it can expand in both directions then would it expand uniformal across rooms? (This is a first floor install over a crawl space.)

A: Wood expands across it’s width, the wider the board, the greater the expansion can be. There are formulas for calculating this, but I don’t have a chart I’m afraid. If this is 2 1/4 wide in a small room, only a 1/2′ gap may be required. Larger room, wider boards, 3/4″. You really need to correct the moisture issue though. Boards cut tight to the side walls will be part of the cause of a floor buckling. Cupping is all about too much moisture.

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