Rate of Wood Shrinkage
Rate of Wood Shrinkage
(OP)
Not so much a structural engineering dilema here, but I havent heard much on the Wood Design forum....
I'm cutting stair stringers out of 2x12's for a set of deck stairs. Based on my elevation changes and rise/run requirements, I have planned out all my dimensions and cuts based on an 11.25" width 2x12.
Now, I go and get my PT 2x12's, and either they just cut the tree yesterday, or soaked the bundle of 2x12's in the river for a month before putting it out for sale (KD19 my a$$). The actual width of these soaking wet 2x12's is 11.5". If I lay out my marks on this 11.5" board based on my 11.25" calculations, I will not have level/straight treads, etc.
So how long will I need to wait before the moisture content of the board gets down to something reasonable and shrinks to the 11.25" width?
I'm cutting stair stringers out of 2x12's for a set of deck stairs. Based on my elevation changes and rise/run requirements, I have planned out all my dimensions and cuts based on an 11.25" width 2x12.
Now, I go and get my PT 2x12's, and either they just cut the tree yesterday, or soaked the bundle of 2x12's in the river for a month before putting it out for sale (KD19 my a$$). The actual width of these soaking wet 2x12's is 11.5". If I lay out my marks on this 11.5" board based on my 11.25" calculations, I will not have level/straight treads, etc.
So how long will I need to wait before the moisture content of the board gets down to something reasonable and shrinks to the 11.25" width?






RE: Rate of Wood Shrinkage
RE: Rate of Wood Shrinkage
In a worst case scenario, where wood has been saturated in the exterior environment, frozen before any evaporation of the moisture, and installated in a building (generally a house) where it is enclosed and then dried in service in a heated area, the shrinkage generally causes severe cosmetic problems, especially where drywall and tile exist. It also creates tilting countertops, when the cabinets are along an exterior wall where the rim joist does not shrink as much because it is greatly affected by the exterior environment.
Also, keep in mind that the cross-grain shrinkage is 30 to 50 times greater than the longitudinal shrinkage. I don't think you'll have dimensional problems, as the lumber generally shrinks evenly, but the slope of your treads could change.
Try to find a better lumber supplier who may have kiln-dried after treatment lumber, and if possible (and this is a big IF) see if you can find treated grade no. 2 or better.
RE: Rate of Wood Shrinkage
RE: Rate of Wood Shrinkage
Just kidding. I dont want to be responsible for you releasing the PT chemicals into your house
RE: Rate of Wood Shrinkage