A recent code change now makes it easier to build with used lumber. Previously, section R104.9.1 required used lumber to be in good condition and free of any obvious areas of decay. It also had to be identified with a grade mark or have a certificate of inspection from a lumber grading agency to verify the strength characteristics. Much of the available used material has no grade stamp; and it is expensive and time consuming to have a lumber grader provide a certificate.
Used lumber still needs to be in good condition and free of obvious areas of decay, but an exception has been added stating used lumber not having a grade stamp or certification shall be assumed to be Douglas Fir-Larch No. 2 and can be used as provided by the lumber span tables for that grade.
This change is intended to make it easier to used salvaged material. Recent requirements by the City of Portland for deconstruction of buildings is likely to make more used material available. There would be very limited use of the salvaged material without the ability to use it in regulated buildings. This change will make it more feasible to recycle dimensional lumber and keep useable material out of the landfill.
Just because the code allows used lumber to be treated as Douglas Fir #2 does not mean it is a good idea to do so in all cases. Some lumber will be found from trees that do not have the strength of Douglas Fir, especially in areas where Ponderosa Pine or Lodgepole Pine is common. There will be some Douglas Fir material that is less than No. 2 grade. Also, the strength characteristics of Douglas Fir has changed over the years and lumber from as recently as 20 years ago is not as strong as the lumber currently coming out of the mills. Lumber with lesser strength used as if it is No. 2 grade could cause structural problems or even building failures.
A wise practice when incorporating used lumber for structural purposes is to evaluate, as best you can, the actual species and grade of the material and use the span tables in the code for the material it most closely resembles instead of the span table for Douglas Fir No. 2.