Washington State is home to two types of termites: subterranean termites and dampwood termites. Subterranean termites are the ones that cause serious structural damage, while dampwood termites infest wet, decaying wood and rarely threaten sound structures. Both are found across the state, from the Puget Sound region to eastern cities like Spokane and the Tri-Cities.
Two Termite Species, Very Different Risks
Subterranean termites live in the soil and tunnel upward into homes, eating through dry or damp wood from the inside out. They build colonies underground and can reach wood that appears perfectly sound. These are the termites that cause real structural damage in Washington.
Dampwood termites, specifically the Pacific dampwood termite, nest inside moist, water-damaged wood. They need consistently wet conditions to survive and don’t build soil tunnels. Because they depend on already-rotting wood, they’re more of an indicator that you have a moisture problem than a structural threat on their own. If the moisture source disappears, dampwood termites typically can’t survive.
Where Termites Are Found in Washington
Washington State University’s Subterranean Termite Mapping Project has documented termite populations across much of the state. Confirmed infestations span the greater Seattle, Tacoma, and Olympia metro areas on the west side, along with Kitsap County communities like Bremerton, Port Orchard, and Poulsbo. On the east side, Spokane, the Tri-Cities (Kennewick, Pasco, Richland), and Yakima all have documented populations.
The WSU mapping data shows termites are predominantly found in loamy soils rather than clay or rocky soils. Since loamy soils exist throughout many areas of the state, subterranean termites can potentially be found well beyond the major metro areas. If your home sits on loose, loamy ground, the risk is higher than if your foundation rests on dense clay or rock.
Signs of Termite Activity
Subterranean termites leave a few telltale signs. The most distinctive is mud tubes: pencil-width tunnels made of soil running along foundation walls, both inside and outside. These tubes connect the underground colony to the wood it’s feeding on. You might spot them on concrete foundations, along basement walls, or in crawl spaces. The wood itself may look intact on the surface but sound hollow when tapped, because termites eat from the inside out.
Dampwood termites are harder to spot because they live entirely within the wood they’re consuming. Look for soft, water-damaged wood around the home, particularly near plumbing, in poorly ventilated crawl spaces, or where gutters have been directing water against the structure. If damaged wood crumbles easily and you find small pellet-like droppings nearby, dampwood termites may be present.
A thorough inspection covers the interior, exterior, crawl space, and attic. Pay special attention to foundation walls, both inside and outside, and anywhere wood contacts or comes close to soil.
Treatment for Subterranean Termites
Subterranean termite control typically requires professional treatment. The traditional method involves applying a liquid termiticide into the soil around and under the building, creating a chemical barrier that prevents termites from reaching the structure. The most reliable modern products are non-repellent, meaning termites can’t detect and avoid them. Instead, termites pass through the treated soil and carry the chemical back to the colony.
The other major approach uses baiting systems. Bait stations are installed in the ground around the home’s perimeter. They contain cellulose material (essentially processed wood) combined with a slow-acting insecticide that disrupts termite growth. Foraging termites find the bait, feed on it, and share it with the colony over weeks, gradually eliminating the population. Several commercial baiting systems are widely used by pest control companies.
Both methods work, but they operate differently. Liquid barriers provide immediate protection and can last years in the soil. Bait systems take longer to work but target the colony itself. Many pest control firms use a combination of both, and the right choice depends on your home’s construction, the severity of the infestation, and soil conditions around the foundation.
Treating Dampwood Termites
Dampwood termites don’t require the same aggressive chemical treatments. Because they depend on consistently moist wood, the fix is eliminating the moisture source. That means repairing plumbing leaks, improving ventilation in crawl spaces and attics, cleaning gutters so water doesn’t pool near the structure, and replacing wood that’s already rotted or been damaged by prolonged moisture. Localized surface sprays may be used in some situations, but removing excess moisture is the primary treatment. Once the wood dries out, dampwood termites can’t sustain a colony.
Preventing Termites in Washington Homes
Moisture control is the single most important factor. Keep the ground around your foundation dry by sloping soil away from the house, maintaining gutters that drain to a low point well away from the perimeter, and avoiding irrigation that sprays the house or saturates soil near the foundation. Installing a footing drain that directs water away from the home adds another layer of protection.
Clearance between wood and soil matters more than most homeowners realize. Maintain at least 18 inches between wooden beams or joists and the soil in crawl spaces. Siding should sit a minimum of 6 inches above soil level, though 8 to 12 inches is better. Crawl space vents need to be at least 6 inches above the ground.
Consider replacing wood mulch and vegetation within 2 feet of the foundation with crushed rock, pea gravel, or concrete pavers. Wood mulch holds moisture and provides a food source, both of which attract termites. Along the same lines, seal gaps around pipes and conduits that penetrate the foundation, since these are common entry points. Preservative-treated or borate-treated lumber for sill plates and other ground-contact framing adds chemical resistance where it matters most.
For new construction or major renovations, physical barriers offer long-term protection. Metal mesh barriers can be installed around foundations, under concrete slabs, or at expansion joints. Sand or basalt particle barriers, installed in trenches around the foundation or under slabs at a minimum depth of 3 inches, physically block termites from passing through because the particles are too large to move and too small to tunnel between. Curing concrete slabs slowly, for at least seven days, reduces the shrinkage cracks that termites exploit to enter a structure.
If you’re buying a home in Washington, a pest inspection is worth the cost regardless of which part of the state you’re in. Subterranean termites have been documented from the wet Puget Sound lowlands to the dry Tri-Cities, and their presence in loamy soils means few areas are truly risk-free.