Well, the party line is that they are 2x4 before they go into the planer and get dimensioned.
I have an older house and some of the interior framing is actually 2xX. However, the house is old enough so that that the boards are only sided on front and back, so the widths are not uniform. Often they didn’t even completely remove the bark.
Two inches by four inches is the rough-sawn dimension, that is, its size when it is first cut from a tree. After surface finishing and drying, the dimension shrinks to roughly 1 1/2 x 3 1/2, give or take, depending on the characteristics of the wood.
When dealing with lumber for woodworking and such it is refered to in 1/4’s and board feet(volume). A 1" board is 4/4, 2" is 8/4 and so on. those are rough cut dimensions so the board in that state is not smooth on any side. So if you had an unfinished peice of board 2" x 4" x 96" after surfacing it it would be 1.5" x 3.5" x 96"
I don’t know why construction went to using surfaced lumber. If you open up a 100 year old house the construction uses true dimensions, the 2x4’s are actualy 2" by 4".
For consistency. As noted previously, rough-cut lumber will not necessarily retain its dimensions after drying along its entire length. Naturally-occurring differences in wood density, quality, moisture content and other factors will cause different parts of the wood to shrink more or less than other parts as the lumber dries. Kiln drying followed by surface planing guarantees dimensional consistency over the entire piece.
Different surface treatments. When you were covering the walls with 3/8" thick wooden lath, 1/2" of brown mud, and 1/8" surface plaster, all applied by hand, there was plenty of room for error in the framing. All framing irregularities were corrected by the plasterer.
Now we are covering the walls with fixed thickness drywall, and any bends and sways in the wall are not easily corrected during the drywall taping.
I’ve heard this explanation before, but I don’t believe it.
Decades ago, in my high school shop class, they said this – but then the finished boards were said to be 1-3/4 x 3-3/4 – only 1/4 inch lost.
Now they claim a finished size of 1-1/2 x 3-1/2 – 1/2 inch is lost in finishing.
So modern planers are worse than older ones, and waste more wood? And it happened all at once; all the wood companies switched to these more wasteful planers at the same time? Hah!
I find it easier to believe that the wood companies simply decided they could make more money by reducing the actual size of a ‘2 x 4’ to something smaller, and got away with it.
I have a retired woodworking friend who makes beautiful hand-made pieces from raw lumber (actual tree limbs) and he says he seldom planes more than 1/16th to 1/8th of an inch away. Yet the big lumber companies let their machines run 4-8 times more waste than this? Again, hah!
Well, it’s not exactly waste to the big lumber companies. the sawdust is used to make particle board. I would be interested to know if the dimensions of finished lumber actually changed after particle board and similar engineered wood products became common.
I recall there was a change to federal regs about 20 years ago regarding the sizing of dimensional lumber. The wood products people claimed that their new methods of drying resulted in less shrinkage, therefore they should be allowed to cut their boards a little smaller so that the final product was the same size as their older boards. The Feds of course agreed, and the result is that boards (magically!) became smaller still.
I’ve tried Googling for more on this, but no luck so far. Anyone else remember this?
I was told about lumber sizes a long time ago by an old carpenter who remembered the changeover from unfinished lumber.
His story was that the lumber mills went to finished lumber for appearance and easier handling in the field. Things like fewer splinters.
The mills’ justification for the smaller size at the same price was that a) you didn’t have to use any more studs and joists of the smaller size and b) more pieces of lumber could be shipped for the same cost. As a result your cost as a consumer wasn’t any higher and you got a nicer looking product that could be handled manually without getting splinters.
Take that for what it’s worth. I guess maybe it computes, sorta, kinda.