Were 2x4s ever really?

by Jonathan Gennick

Fair warning: this weblog entry has absolutely nothing to do with computers.

I'm doing some minor remodelling in my house, which is a somewhat older house built in the early 1950s. Tonight I've been installing furring strips for a new basement-bathroom ceiling, and all that working with wood has resurrected some long-standing questions I've had about lumber sizes.

Consider the lowly 2x4, that staple of home construction. The 2x4s I buy today are actually 1 1/2 x 3 1/2. Ok, I understand, and maybe I'm wrong about this, that half an inch in either dimension is lost to the kerf from the saw blade and the subsequent sanding required to get a smooth finish on the board. Frankly, that seems a lot to lose from sawing and sanding, but ok. However, in my house are many old 2x4s, and all of those are 1 3/4 x 3 9/16. Why? Were saw-blades thinner in the old days? At what point did this great transition occur, and why? It's not just my house, by the way. Consistently I see 2x lumber in older houses that is 1/4-inch thicker than any 2x lumber I can buy today.

My second long-standing question concerns edges. I can go to the homestore and buy all sorts of 1x lumber with squared-off edges. But any 2x lumber that I buy always has rounded edges. Why is that? The rounded edges don't blend too well with the squared edges on all the 2x lumber in my house. You see, whenever it was that 2x lumber shrunk in size, that must be when it picked up the rounded edges too.

In the grand scheme of things, these are trivial questions, but I'm sure there's an interesting story behind the answers. And that's what I want, to find the interesting story.

Do you know why lumber sizes changed, and when? Do you know why the edges of 2x lumber are rounded instead of squared? If you do, please post. I want to know too.


2002-10-15 02:36:01
2x4 or not
In the UK if you ak for a 2x4 you would usually get a piece of wood that is actually 50mm x 100mm (minus a bit for cutting), our builders went metric quite a while ago, but still use the old names. The metric size is slighter smaller.

Maybe that's the reason for the effect you're seeing.

Jonathan Gennick
2002-10-15 05:56:05
2x4 or not
That's really interesting. I just measured one of my 2x4s (a new one) with the metric side of a ruler and came up with dimensions of 38mm x 89mm. That's smaller than yours. I think I have 2x4 envy now.

You know, Canada's on the metric system, and I live only an hour an a half or so from Sault Ste. Marie, Ontario. Next time I get out that way, I'm going to hop across the boarder, buy a 2x4, and see what I get.

2002-10-15 06:31:01
2x4 or not
http://www.woodforgood.com/building/scomp/sizes.htm has a load of info on wood sizings, table 4 is especially relevant. American and Canadian standard 2x4s seem to be 38mm x 89mm (with rounded arasses) as you've discovered.

I was guessing a little earlier at 2x4s in the UK being 50mm x 100mm, looking at that website they're more likely to be 47mm x 100mm or even 47mm x 97mm


2002-10-15 07:24:20
While I can not explain the differences between old 2x4s and newer 2x4s, one big reason that the wood is not actually 2x4 is that the measurement is taken well before any curing of the wood. That is, the uncurred wood is initially cut at 2x4, and then left to dry out and cure. I think it is the curing that accounts for the greatest percentage of the shrinkage.
2002-10-16 04:07:21
2x4 or not
Just to complicate matters, I can buy 100mmx50mm in my local woodyard, but all the lengths are in feet and inches :-)
2002-10-16 09:14:48
2x4s aren't 2x4 because they can get away with making them smaller (thanks to the standards in this area). Even rough cut 2x4s are cut well under 2x4 (and no, blade size is not a factor). It may be the case that there was a fair reason for setting the standard size so small, but I would imagine that it was good ole fashioned lobbying.
2002-10-18 08:58:04
Those were the days
I grew up in a family of three generations of home builders and remodelers. Before I started working with computers I was a carpenter myself. My father and his brothers owned a large lumber yard in Westmont, IL. I start working with my father during the summer when I was eight years old--and was always scolded for asking too many damnned questions. Regardless, I asked all the old guys for "history of" on everything that came to mind. I also had several opportunities to work on houses over 200 years old. From that experiance and hearsay, here's my take:
In the old houses we remodeled, 2x4s were actually rough-sawn 2 x 4 inches (or larger). I recall my Uncle Leonard talking about his grandfather hand sawing timber into 2x4s. When the industrial age (manufacturing in early 1900's) became a reality in the U.S., 2x4's were still rough sawn at approximately 2x4 inches, but now by machines. As an improvement to handling them on the job, they eventually became planed (smoothed) from the original rough sawn 2x4 stock. This created a 3 3/4 x 1 1/4 inch 2x4. As building codes were established, they specified the minimum number of 2x4's that could be used in a wall and other applications. Then, as mechanical engineering improved in the residential building trades, actual load brearing tests revealed that less lumber could be used (conservation of lumber) and the existing building codes could still be met. So now we have roughly a 3.5 x 1.5 inch 2x4 (or smaller at some home improvement stores). Yes, just like everywhere else, those engineers under the orders of the accountants conserved raw material to increase profit and the availablility of a fixed resource. That's about 500 kid questions--and all the adults irritated by them--condensed into one paragraph. That's my story and I'm sticking to it.
2002-10-29 07:13:33
2x4 sizes
I too like Balesd worked the trades before taking on a job with these infernal machines. Lumber size was reduced as the timber was dressed not just for pretty sake but a rough sawn 2x4 can vary wildly in size all on it's own. Dressing the timber makes it easier to expect a consistent size when building. Economics are one factor that size has been reduced from earlier timbers to todays roughly current 3 1/2 x 1 1/2 but another is it's a very sad fact as things stand today we may see in our lifetime clear 1x12 lumber becoming as precious as a mint Mickey Mantle baseball card. Shaving a quarter inch off a dimension may seem trivial at the consumer level but it translates into millions of board feet of extra production from the mills that crank this stuff out.