THE TRUTH ABOUT OLD GROWTH VS. NEW GROWTH FRAMING LUMBER
There is a widespread belief in the construction and carpentry world that old-growth lumber is inherently better than the new-growth lumber being harvested and milled today. While older wood certainly has a tighter grain and unique characteristics, the real question is whether modern new-growth lumber is structurally deficient for today's building standards. To find out, we need to look past the rumors and dig into the actual compressive strength numbers required by structural engineers.
UNDERSTANDING FLOOR JOIST SPAN REQUIREMENTS
When structural engineers create span charts for rafters and floor framing, they establish strict baselines for safety. These charts determine the minimum compressive strength, measured in pounds per square inch (PSI), required to safely support a load over a specific distance.
The minimum compression rate varies depending on the length of the lumber. For example, the minimum compression PSI rating for a standard 16-foot long floor joist is 237 PSI. If you extend that span to a 24-foot long floor joist, the minimum required compressive strength increases to 356 PSI. These are the hard numbers required to ensure a floor system will not fail under standard residential loads.
COMPARING THE COMPRESSIVE STRENGTH OF DOUGLAS FIR
To see how modern and historical wood stacks up against these engineering requirements, we can look at university survey data testing the strength of Douglas Fir. While variables like the exact age of the lumber and the specific harvest location play a role, the baseline averages are highly revealing.
According to the testing data, old-growth Douglas Fir tested at a compressive strength of 567 PSI. The new-growth lumber, on the other hand, tested at 464 PSI. It is true that the old-growth wood holds a higher PSI rating, which validates the idea that older wood is denser.
WHY NEW GROWTH LUMBER IS MORE THAN ENOUGH
While the older wood is technically stronger, that extra strength is largely unnecessary for standard residential framing. If the strict engineering minimum for a long 24-foot floor joist is only 356 PSI, the 464 PSI rating of new-growth Douglas Fir easily exceeds the requirement.
The difference in strength between the two generations of wood does not make a functional difference in standard framing applications. Modern homes are not suffering from structural failure due to the compressive strength of new joists and roof rafters. Until modern lumber starts causing framing to fail, there is no structural need to worry about using standard new-growth dimensional lumber.
THE PRACTICAL DRAWBACKS OF OLD GROWTH LUMBER
Beyond the numbers, there are practical job site realities to consider. Reclaiming used lumber from an old house or working with dense, old-growth wood can actually slow down a project.
Because of its high density, old-growth lumber is significantly harder to cut. Furthermore, it is notoriously brittle when it comes to fastening. Carpenters frequently experience splitting when trying to drive a toenail into old, hardened lumber. While the elevated compressive strength of older wood sounds great on paper, it often translates to a frustrating, labor-intensive framing process in the real world.
Ultimately, modern new-growth lumber meets all necessary engineering codes, is easier to work with, and provides plenty of strength for a safe, durable home.
THREE KEY TIPS
ALWAYS CHECK YOUR SPAN CHARTS: Never guess on joist lengths. Always consult local building codes and engineered span charts for the specific species and grade of wood you are using, as a 2x10 of Pine will span differently than a 2x10 of Douglas Fir.
PRE-DRILL RECLAIMED WOOD: If you do choose to build with reclaimed or old-growth lumber, save yourself the headache of split boards by pre-drilling your fastener holes, especially when toenailing or working near the end of a board.
INSPECT FOR CROWN: Regardless of whether your lumber is old or new, always sight down the edge of your joists before installing them to find the natural curve or "crown." Always install joists with the crown facing up so the weight of the floor settles the board into a flat position.
BONUS QUESTIONS AND ANSWERS
DOES MOISTURE CONTENT AFFECT THE COMPRESSIVE STRENGTH OF FRAMING LUMBER?
While compressive strength is a major factor in framing, another element heavily regulates how wood performs once it is sealed inside your walls. Building codes strictly regulate the moisture content of framing lumber, typically requiring it to be dried to 19 percent or less before installation. If wood is framed while too wet, it will shrink, twist, and warp as it dries out, which severely compromises its load-bearing capacity and leads to severe drywall cracking. To ensure your framing material is ready for drywall, it is always a smart practice to check the wood with a digital moisture meter before hanging your insulation.
HOW DO KNOTS AND WOOD DEFECTS IMPACT THE STRUCTURAL GRADING OF LUMBER?
Beyond the overall age or species of the tree, the physical characteristics of individual boards play a massive role in building safety. Code span tables rely on specific lumber grades, such as No. 1 or No. 2 structural lumber, which are assigned by inspectors who look for defects like knots, checks, and splits. These imperfections disrupt the continuous grain of the wood, creating weak points that significantly lower both the bending and compressive strength of that specific board. If a span requires extreme strength and clear dimensional lumber is unavailable, builders will often upgrade to engineered wood products like LVL (Laminated Veneer Lumber) beams, which manufacture out these natural defects entirely.
WHAT ROLE DOES BLOCKING OR BRIDGING PLAY IN FLOOR JOIST STABILITY?
Even if you select the densest, highest-quality Douglas Fir available, a floor system is only as strong as its lateral support. Building codes generally require solid wood blocking or metal cross-bridging at specific intervals along long joist spans to keep the floor structurally sound. This lateral bracing prevents the tall joists from twisting or rolling over under heavy dynamic loads, and it helps distribute localized weight across multiple framing members to prevent floor bounce. When installing solid blocking, applying a heavy-duty construction adhesive, like PL Premium, to the edges before securing them with a framing nailer is the best way to prevent squeaky floors in the future.
