Q: I am building a new house and I am interested in wider boards of about 5 inches, but I have heard these can have problems with cupping.
Is this true and if it is, is there a way to avoid the problem?
A: The wider the board, the greater is the chance of cupping. Having said that, the only thing which causes this to happen is excess moisture in the wood itself, either from poor climate control in the house, from installing over a crawl space that has not had steps taken to prevent moisture from rising up under the floor, and such things as this. Make sure you leave at least a 1/2 gap along the walls to allow for any expansion that may occur. The wider the board, the more mass to expand. I believe quarter sawn is much less likely to be affected by this problem at all, though it may be more expensive.
Make sure when this floor is installed that you let it acclimate to the rooms for at least a week. All wet trades must be completed with the heating/air-conditioning in place and functional. Make sure the sub floor is within 4% of the wood flooring as far as moisture content. 7-9% is considered normal range for wood such as oak. If the plywood is reading 20% don’t install the floor.