By what percentage does lumber decrease in strength when pressure treated?

The correct answer indicates that lumber experiences a decrease in strength of approximately 25% when it undergoes pressure treatment. This reduction in strength is primarily due to the chemical processes involved in pressure treating wood, which can alter its physical and mechanical properties.

When lumber is pressure treated, it is infused with chemical preservatives that help protect it against decay, insects, and other environmental factors. However, the infusion of these chemicals can add weight and change the internal structure of the wood fibers. As a result, the overall strength of the wood can diminish, with studies and practical guidelines suggesting that a reduction of about 25% is a reasonable estimate for many types of treated lumber.

Understanding this decrease is crucial for builders, architects, and fire inspectors because it affects the load-bearing capacity of structures utilizing pressure-treated wood. Such knowledge is essential to ensure that structures remain safe and comply with building codes and standards.