Do 4″ wide planks need to be edge glued?

Q: We were recently told by a veteran wood flooring contractor that if we wanted to install solid wood flooring that was 4″ wide planks or more, it would need to be edge glued. When we asked some local wood retailers about this, they said they’d never heard this theory and basically said larger size widths are nailed down just like the narrow widths.

Can you offer some clarification on this?

A: 4″ Isn’t that wide. The wider the board, the closer the nail spacing should be. If you go beyond 4″ I would recommend ‘end’ gluing. The wider the board the greater potential for expansion, contraction and cupping if the environment is not well controlled.

Similar Q: I want to use shiplap for a floor and fasten it with square headed nails. Would you recommend gluing as well?

A: If the boards are 5 or more inches wide I’d probably glue the ends of the boards. There is a likely chance as with most things, you will get some movement because of changes in temperature and humidity. I don’t think you necessarily want to try to prevent that because you will fail and if there is big movement something will break. If you do use an adhesive I’d find something that stays flexible. I’m not against using adhesive though.