Dimensional lumber used in framing (i.e., 2×4, 2×6, etc.) is usually sold after planing and kiln drying. That’s why a 2×4 is actually 1.5″ x 3.5″. The stick of lumber from which that 2×4 was made was originally sawn to dimensions of 2″ x 4″. The length of these “rough sawn” boards is the nominal length plus at least 2 inches. So an 8′ 2×4 in rough-sawn form is 2″ x 4″ x 98+”.
You can buy rough-sawn lumber at most saw mills. Most of the time what you buy is “air dry” from stacks that have sat out in the mill’s yard for a year or so. The moisture content is still high, say 20%, but nothing like true green lumber right off the saw.
The main advantages of rough-sawn lumber are:
- 50% greater cross-sectional area (for a 2×4), which makes it stronger and stiffer. This is highly significant in bending/beam applications as with joists and rafters.
- Rustic appearance from the raw sawn surfaces.
- Lower environmental footprint from reduced transportation and processing costs.
- Supporting local saw business (the saw mill, the loggers, and the wood lot owners).
The main disadvantages of rough-sawn lumber are:
- Weight…more than 50% heavier for a 2×4. This only really matters if you’re hauling it a significant distance.
- Varied appearance due to weathering in saw mill’s yard.
- Variation in length of 1/8″ – 1/4″.
- Shrinking possible across the grain (but not typically along the grain).
Interestingly, rough-sawn lumber is not usually cheaper than conventional finished lumber, especially for 2x4s. The big box retailers like Home Depot and Lowes price their 2x4s as loss leaders; so low that there aren’t many local saw mills that can compete on price. Still, the dimensional lumber is not a very big expensive item on most projects, so the price differences don’t matter much.
Some of my research suggested that rough-sawn would not be as straight as conventional lumber. I didn’t find that to be true. The dimensional lumber at most lumber yards is not the nicest wood…it can be warped and full of knots. I found that the rough sawn from my local mill was, if anything, straighter than what I could get at the lumber yard.
I found working with rough sawn no problem at all. The only thing that requires some attention is the lengths of the sticks. You can take one of two approaches: you can sort the lumber a bit so that the differences between adjacent sticks are not too great and just live with it, or you can trim each stick to length. I mostly took the “live with it” approach and ended up with a structure that was very plumb and true.