29 October 2021

A "2X4" is not 2" x 4" in size


How did I get to my age without knowing this?
In the Americas, two-bys (2×4s, 2×6s, 2×8s, 2×10s, and 2×12s), named for traditional board thickness in inches, along with the 4×4 (89 mm × 89 mm), are common lumber sizes used in modern construction. They are the basic building blocks for such common structures as balloon-frame or platform-frame housing. Dimensional lumber made from softwood is typically used for construction, while hardwood boards are more commonly used for making cabinets or furniture.

Lumber's nominal dimensions are larger than the actual standard dimensions of finished lumber. Historically, the nominal dimensions were the size of the green (not dried), rough (unfinished) boards that eventually became smaller finished lumber through drying and planing (to smooth the wood). Today, the standards specify the final finished dimensions and the mill cuts the logs to whatever size it needs to achieve those final dimensions. Typically, that rough cut is smaller than the nominal dimensions because modern technology makes it possible to use the logs more efficiently. For example, a "2×4" board historically started out as a green, rough board actually 2 by 4 inches (51 mm × 102 mm). After drying and planing, it would be smaller by a nonstandard amount. Today, a "2×4" board starts out as something smaller than 2 inches by 4 inches and not specified by standards, and after drying and planing is minimally 1+1⁄2 by 3+1⁄2 inches (38 mm × 89 mm).
You learn something every day.  Photo via Reddit.

8 comments:

  1. Another factoid about lumber. One reason lumber is planed and the corners rounded is to help stop fire from spreading as quickly. The "furry" sides and sharp corners catch fire more easily than the smooth sides of modern lumber.

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  2. Long time builder here, its all about the money...

    Downsize for the same price or higher.

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  3. Based on the photo alone, I would have guessed Shrinkflation. https://en.wikipedia.org/wiki/Shrinkflation

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  4. This is one reason it's so hard to repair a hundred-year-old house. It's a pain to replace wood when you can't get the same size wood.

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    1. I live in a 1917 bungalow. Did extensive remodeling,correcting bad alterations from the past. Framing is not difficult, but requires furring on the interior: New lumber is flush with exterior siding, but interior dimensions are then short. Not rocket science, but a little labor intensive. No one uses the "same size wood." Pretty much impossible to buy other to have it custom milled.

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  5. Another fun thing to notice in the lumber is the rings. That 1920 piece was taken from a much smaller tree, but the rings are still pretty tight. The rings on the 2019 are much further apart, demonstrating how much more quickly trees grow now through optimized cultivation. However, the 2019 pine will be much, much less dense and far softer because of this.

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    1. Old growth lumber found in antique houses is far superior. True that.

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  6. If you are looking for lumber that is a full inch thick, ask for 5/4 (five quarter) boards. These are usually used as decking, but come in handy for repairs on older houses.

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