Just how straight is kiln dried lumber?

[Jared Drake]

So, we finally got some land. And got it paid off. Now it's time to buckle down and settle on a house plan on details. Is kiln dried whitewood straighter than SYP? Is it worth the extra money? The reason I'm asking is because I want 12-14 foot sidewalls for a little extra headroom upstairs rather than building a short pony wall on a platform upstairs (I'm told that would create a "hinge-point"). I'm trying to get an estimate of how much lumber and how much money it'll take to frame up a 20x24 or 24x24 building.
Jared

[UK4X4]

as straight as the guy who picks it !

I hate delivered timber- what ever is on the lable

I'm the guy in the box store moving 20 long bow candidates to get at the straight ones down in the pile.

you can get engineered studs these days if you want the quality and don't mind the price !


But I'll leave it to Don for the technical edge......me I'm just a fussy shopper according to the wife

the last deck i built at the cabin -I recon the picked timber saved me about three hours over the delivered stack

[Don_P]

Moisture change is what makes wood move. KD framing is normally 19% but it will dry down to 8-14% in typical service. This is why a bundle of lumber can fly open when you cut the bands, it has dried and moved more. For fine work we specify closer to that equilibrium moisture content, flooring for instance comes in at 8-10%mc. In the cabinet shop I would try to be fair with everyone and knew I could get away with 12% in the south, I turned trucks around at 13% and ruined everyones day.

They've recently derated syp in #2 grades to where it is now one of the weakest woods. Wood bows, twists, crooks and cups, the only one that is the kilns fault is cup and that is rarely the problem in syp. It is one of the fastest drying woods, cup occurs when the kiln is running too slow. They hammer syp and it can take it, the cells are built for drying as opposed to something like white oak that dries at glacial speed.

Since dry wood is about twice as strong as green, generally if you can quickly dry the shell of a board it helps hold it in place during the rest of drying whereas air dried slowly develops strength and may move more in the process. Drying is like driving between ditches, to the left is cup and mold from going too slow, the right ditch is a pile of checked cracked lumber from shrinking that rapidly drying outer shell too fast and it cracks over the still swollen core.

Most of what causes deformation is twisted grain or "reaction wood", abnormal grain. In syp that reaction wood is from a big juvenile heart as well as compression wood caused by too rapid growth. In both cases the microfibers that make up the cell walls, rather than being aligned with the length of the tree, lay at an angle to the axis. Normal fibers on one side of a board that shrink only in width but not length coupled with reaction wood on the other side of the board that shrinks in both length and width is a recipe for a curve.
SPF is now rated stronger than SYP in #2. You used the term whitewood, if the stamp has european countries of origin run like the wind, weak eurotrash.

All that is just for wood tech info, I believe there is a thinking problem structurally. If you are trying to resist outward thrust with a stud you're backing up. It sounds like a situation that calls for a structural ridge beam I think.

[Erin]

I'm with UK, I never just take delivery.  I've hand-picked absolutely every board in my house. 
Consequently, it's all straight and pretty.  (Well, except the ones that are crooked because I picked them instead.  )

To the question of SYP vs. "whitewood", assuming #1 in both cases, SYP tends to turn into bananas as it dries beyond that minimal 19%.  So, either skip it and size up for SPF or, install it immediately.  Even then you might continue to fight the bow...