How much will an undried hardwood shrink in the axial direction?

Question

At the hardwood mill the man at desk said that the wood they cut (red and white oak, and poplar plus maple and others) is not kiln dried and can shrink as much as 6%. That makes sense to me and of course I would not build furniture with it, but for my application some shrinkage is not an issue width-wise.

My question is whether that 6% value is accurate for the axial/long/grain direction. Considering an 8' long piece of oak 2x4 or 1x4, which is 96", I find it hard to believe it would shrink just shy of 6 inches in length when kiln dried. I could picture an inch maybe, but 6", not so much. Is my assessment accurate on this?

Answer 1

Wood behaves anisotropically (differently in different directions.)

Common values for radial, tangential, and axial (aka longitudinal) shrinkage in red oak are 4%, 8.6% and 0.1-0.2% (not even called out in the data, but provided at the shrinkage information page, generically for all wood.)

So, in the direction you care about, 0.1-0.2% so between 3/32 and 3/16 of an inch for a 96 inch board.

If you are willing to dry it first (kiln drying is not required, it's just faster) you can certainly build furniture with air-dried wood. Or you can set up a simple lumber kiln, using plastic, sunlight, and fans and kiln-dry it yourself.