Wooden fence cladding is common here, they're the fences between neighbors that use horizontal wooden cladding attached to a fence post.
Douglas fir is a popular choice, which can expand a lot during rainy days.
The recommendation is always to leave some horizontal spacing between the individual boards to allow for wood movement.
But another recommendation is always to use 2 screws on either side of the board (so 4 screws per board) when attaching it to the fence posts to prevent the board from cupping and warping.
Why don't these two screws cause issues? Why doesn't the wood split and fly off the fence posts when it expands? It seems completely restricted by the screws, and is constantly under changing moisture conditions outside. Is it because individual wood fibers don't run all the way through the wood and leaving space between boards is enough?
Can anyone help me answer why on the one hand you need to leave space between each board to allow for wood movement, and on the other you are screwing it down with 2 screws on each site, seemingly preventing wood movement. Thanks.
After looking through several books regarding building codes, using fasteners in this way does cause issues with many species of wood. To avoid this, oversized pilot holes should be used so the wood can move to minimize tension on the screws. Countersinks should be avoided and wide flat screw heads should be used instead.
What I don't understand is why this system of using fasteners on cladding and decks is so popular when it doesn't allow for wood movement and many building codes advise against it.