Wood shrinkage 1

[LPPE]

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?

 

[boo1]

What probably happened is the boards were not re-dried after pressure treatment. Typical PT in central and eastern U.S. is southern pine. The fiber saturation level is reached when it holds moisture content of about 28%. The wood shrinks approximately 1% for every 4 percent points below the 28% level. Experience has shown that lumber dried to 19% moisture content, installed outdoors, will undergo limited dimensional changes.

I have let wet PT boards dry for 30 days with good results. Local humidity and temperature will influence you air-drying time. Ensure good ventilations.

Cheers

 

[ctmtwilliams]

I don't know where you live but here in California nomimal 2x12 (commonly Duglas Fir) is 1.5 x 11.5, and the same goes for PT lumber. I wouldn't expect 0.25 of shrinkage in width with PT lumber.

 

[boo1]

Common diminsional size of 4S-2"x12" softwood though out the U.S are 1.5" x 11.25".

 

[ctmtwilliams]

My bad, 1.5 x 11.25 is correct, sorry.

 

[LPPE]

I currently reside in the Northeast.

Unfortunately, all the PT lumber we get around here seems to be soaked. And normally you dont have the space to lay it out and cant wait 30 days for it to dry. It's unfortunate, but you lay out your 5/4x6 deck boards with a 16d nail gap between each board, and in couple months the gap has widened to almost 1/2".

It's really too bad the lumber yards dont seem to care about what quality of lumber they provide. Even framing lumber is similar. It's stamped KD19, and its damp to the touch. Drive a nail, and you get water splattering up at you. Why pay the extra for KD when its not? False advertising.

 

[boo1]

Less than 10 percent of all treated wood is kiln dried after treatment, and supplied only on request. (KDAT appears in the quality mark.) If you can’t wait for the wood to stabilize or need a better fitting product ,request the KDAT products. Even then .....

See for study at link at:

http://www.fpl.fs.fed.us/documnts/pdf2001/shupe01a.pdf

Note: With the SYP TP, pre-drilling hole within two inches of the ends prior to nailing reduces splitting.