Graded Lumber and the Building Code
Most houses in Tennessee are framed with wood. Even if the outside has brick or stone siding, chances are that the structure of the floor, walls and roofs is made of softwood lumber. Most of the lumber used in building comes from large sawmills, but can the do-it-yourselfer with a portable sawmill use “home-made” lumber for their building projects? Maybe not...
Because the safety and lasting value of your house depends on structural integrity of the framing, a system of lumber grading has been devised to ensure that the wood pieces that are used in building construction are up to the task. The U. S. Department of Commerce has established the American Softwood Lumber Standard PS 20-70 that covers the requirements for structural lumber. This grading system takes into account such factors as knots and grain pattern to predict the performance characteristics of the wood. Lumber grading is usually done by specially trained personnel at sawmills who visually inspect each piece of lumber. Lumber produced at these mills carries a stamp that lists the grade, species, grading authority and producing mill.
Many building codes specify the use of certain grades of lumber for specific applications. In these cases, un-graded lumber cannot be used. It is possible to hire an inspector to grade your lumber and qualified graders can be located through one of the major grading agencies, for example the Southern Pine Inspection Bureau. However, at a cost of over $300 per day plus expenses, hiring you own grader can make your lumber more expensive than the factory-produced alternative.
In addition to carrying a grade stamp that satisfies the building code, lumber produced at sawmills has other advantages. Modern milling technology results in lumber that is often more uniform in size than the “rough sawn” lumber produced on portable sawmills. It is true that you can cut construction lumber that is a full 2” thick by 4” wide on a portable sawmill (as compared with the actual 1 ½” by 3 ½” dimensions of factory-produced “2X4”). However, this is not necessarily an advantage. Construction practices and accessories have been developed around the dimensions of factory-produced lumber. So, while a bigger piece of lumber may be stronger, the smaller, standard dimensions of factory-produced lumber are strong enough for normal building practices. Nails, insulation and other construction materials have been sized to fit the standard sizes too. Finally, most factory-produced lumber available in Tennessee (often southern pine) has been kiln dried. This reduces the weight of the lumber and helps to reduce the risk of mold and rot.
Cutting your own lumber or using wood from your own trees can be satisfying and can save money in some applications. However, using your own wood for framing lumber may not be “worth it” in the long run.