Can we talk about how much wood actually moves after it's milled?

I found out today from a guy at the lumber yard that a 2x6 can shrink by almost a quarter inch across the face if it goes from 20% moisture down to 8%. That just blew my mind because I've been building decks for years and never really stopped to think about that kind of movement. How do you all account for seasonal changes when you're framing something that has to stay square?

2 comments

2 Comments

betty_shah3d ago

Yeah that 20% to 8% moisture swing is a bigger deal than most folks realize. The guy at the yard was talking about that quarter inch per 6 inch face, but for a 12 foot 2x6 that can add up to almost half an inch across the whole board if it's really wet to start. What I do is try to let my lumber sit on site for a few weeks before cutting anything critical, at least give it time to adjust to the local humidity. For decks I always leave a little extra gap between boards and use those hidden fasteners that let things move without buckling. Do you guys ever bother with kiln dried for exterior stuff or just use pressure treated and hope for the best?

john_hunt23d ago

Twenty years in construction and I still forget how much that green lumber moves. Drives me nuts when a deck rail buckles six months later.