Termites can eat pressure treated wood, but they generally avoid it. The chemicals infused into pressure treated lumber are toxic to termites, making it far more resistant than untreated wood. However, “resistant” is not the same as “termite-proof,” and under certain conditions, termites will feed on pressure treated lumber, sometimes causing serious damage.
How Pressure Treatment Deters Termites
Pressure treated wood is created by forcing chemical preservatives deep into the wood fibers under high pressure. The goal is to saturate the wood with biocides that kill the organisms responsible for decay, including fungi, bacteria, and insects like termites. The core ingredient in most modern formulations is copper, which acts as both a fungicide and an insecticide. Different products add other active ingredients: tebuconazole and propiconazole target fungi, while some formulations include compounds specifically designed to kill insects.
When a termite bites into properly treated wood, it ingests these chemicals. Copper disrupts the termite’s biology at the cellular level, and the insecticidal compounds can be lethal even in small amounts. Some chemical treatments go a step further by making the wood hydrophobic, meaning it repels water, which also makes the wood essentially unrecognizable to the digestive enzymes termites rely on to break down cellulose. Without the ability to digest the wood, termites get no nutritional benefit from eating it.
When Termites Attack Treated Wood
Despite the chemical protection, there are real-world scenarios where termites successfully feed on pressure treated lumber. The most common reasons come down to inconsistent chemical penetration, aging, and extreme termite pressure.
- Uneven chemical absorption. Pressure treatment doesn’t always penetrate evenly throughout the wood. The heartwood of some species resists absorbing preservatives, leaving pockets of essentially untreated material. If termites find these areas, they can tunnel through them just as easily as untreated lumber. Cuts, notches, and drill holes made after treatment expose completely untreated interior wood.
- Chemical degradation over time. The preservatives in pressure treated wood don’t last forever. Exposure to rain, soil moisture, and UV light gradually leaches or breaks down the active chemicals. Wood that was well-protected when installed may lose effectiveness over the course of 10 to 20 years, especially in regions with heavy rainfall or high soil moisture.
- Formosan subterranean termites. Not all termite species respond the same way to treated wood. Formosan subterranean termites, found across the southern United States, are notably more aggressive than native species. Colonies can number in the millions, and their sheer volume means some workers will push through treated wood that would deter smaller colonies. They’ve been documented causing damage to pressure treated structures, particularly where chemical retention is on the lower end.
- Insufficient retention levels. Pressure treated wood comes in different grades based on how much preservative it retains. Wood rated for above-ground use has a lower chemical concentration than wood rated for ground contact. If you use above-ground rated lumber in soil or in consistently damp conditions, termites are far more likely to attack it. The wood simply doesn’t contain enough preservative to hold up under those conditions.
Use Categories and Retention Levels
The American Wood Protection Association (AWPA) classifies treated wood into five use categories based on how much biological threat the wood will face. The categories range from interior use with no weather exposure all the way to permanent submersion in salt water. Each category specifies a minimum chemical retention level, which is the amount of preservative that must be present per cubic foot of wood.
For termite resistance, the category matters more than most people realize. Wood intended for ground contact requires significantly higher preservative levels than wood used for a deck railing or fence picket that never touches soil. If you’re building something that will sit in or on the ground, especially in termite-heavy regions, you need lumber rated for ground contact or higher. Using the wrong category is one of the most common reasons pressure treated wood fails to stop termites.
Where Treated Wood Is Most Vulnerable
The places termites are most likely to attack treated wood are predictable. Any spot where the wood stays consistently moist is at higher risk, because moisture accelerates chemical leaching and also attracts termites in the first place. Subterranean termites need moisture to survive, so they gravitate toward damp wood regardless of treatment.
Posts set directly into the ground are a common failure point. Even with ground-contact rated lumber, the buried portion of a post sits in constant contact with soil moisture and the termite colonies living in that soil. Over years, the preservative concentration drops while the termite pressure stays constant. Deck ledger boards, where a deck attaches to a house, are another frequent problem area because they can trap moisture between the deck frame and the home’s exterior wall.
Field cuts deserve special attention. Every time you saw, drill, or notch pressure treated lumber on a job site, you expose raw, untreated wood. Applying an end-cut preservative solution to these exposed surfaces is the standard recommendation, but it provides far less protection than the original factory treatment. Termites can and do enter through these weak points.
How to Maximize Termite Resistance
Pressure treated wood works best as one layer in a broader termite prevention strategy, not as a standalone solution. Choosing the right retention level for your application is the starting point. For anything touching the ground in a termite-prone area, select wood rated for ground contact at minimum.
Reducing moisture around treated wood extends its protective life significantly. Good drainage, proper flashing, and avoiding soil-to-wood contact where possible all help the preservatives last longer. When you make field cuts, coat every exposed surface with a brush-on preservative rated for end cuts.
Physical and chemical termite barriers around foundations add another line of defense. Stainless steel mesh barriers, sand barriers, and soil-applied termiticides create zones that termites struggle to cross before they ever reach the wood. Regular inspections, particularly of ground-contact areas, catch early damage before it becomes structural. In high-risk regions like the Gulf Coast and Southeast, annual inspections are standard practice even when pressure treated wood is used throughout the structure.
Pressure treated wood dramatically reduces the likelihood of termite damage compared to untreated lumber, but it does not eliminate the risk entirely. Thinking of it as termite-resistant rather than termite-proof will lead to better building decisions and fewer surprises down the line.