Bathrooms are one of the most common places termites show up inside a home, thanks to the constant moisture around plumbing, showers, and poorly ventilated walls. Treating termites in a bathroom depends on two things: the type of termite you’re dealing with and how far the damage has spread. A minor, localized infestation can cost as little as $75 to treat, while more complex cases run between $263 and $1,032, with severe infestations reaching $1,750 or more.
Identify the Type of Termite First
Before you can treat anything, you need to know what you’re looking at. The two types most likely to appear in a bathroom are subterranean termites and drywood termites, and they leave very different evidence behind.
Subterranean termites build mud tubes, pencil-width tunnels made from soil, wood, and saliva that connect their underground colony to the wood they’re eating. These tubes are typically 1/4 to 1 inch in diameter and show up along foundations, basement walls, and sills. In a bathroom, they’re often hidden behind baseboards, inside wall cavities near plumbing, or in the crawlspace beneath the bathroom floor. A damaged subfloor may start to sag, and you might notice tile pulling away from the surface underneath it.
Drywood termites don’t need soil contact or as much moisture. Their telltale sign is frass: tiny oval-shaped pellets about 1 millimeter long, with six concave sides and rounded ends. These pellets collect in small mounds that look like piles of salt or pepper beneath “kick-out holes,” small openings the termites push their droppings through. The color of the frass matches whatever wood the termites have been eating. If you see pin-sized holes in drywall or wood trim near your bathroom with little pellet piles below them, you’re likely dealing with drywood termites.
Why Bathrooms Are Especially Vulnerable
Termites are drawn to moisture, and bathrooms provide it constantly. Leaking supply lines, slow drains, condensation on pipes, and poor exhaust ventilation all soften wood and make it easier for termites to consume. Subterranean termites in particular thrive where soil moisture meets wood framing, which is exactly what happens when a bathroom sits on a slab or above a damp crawlspace. Even small, chronic leaks behind walls can create conditions that attract a colony and go unnoticed for months or years.
Foam Treatments for Wall Cavities
For termites inside bathroom walls, expanding foam termiticides are one of the most effective localized treatments. The foam is injected directly into wall voids where it expands to fill gaps and coat surfaces that liquid sprays can’t reach. Here’s how it works in practice:
- Locate the activity. Look for mud tubes, damaged wood, sagging drywall, or frass piles. In bathrooms, check around the base of the toilet, behind vanity cabinets, along baseboards, and near any plumbing penetrations in the wall.
- Drill small access holes. Small holes are drilled into the infested wood or drywall to create entry points into the wall cavity. These are typically placed near confirmed termite activity.
- Inject foam slowly. The foam is injected gradually so it has time to expand and fill the entire void, reaching termites that would be impossible to target with a surface spray.
Foam products used for this purpose contain active ingredients like fipronil, which disrupts the nervous system of insects on contact. What makes fipronil particularly effective against termites is the “transfer effect.” Termites that contact the chemical carry it back to the colony, spreading it to other members through normal grooming and feeding behavior. This means the treatment reaches termites you never see.
Liquid Barrier and Bait Treatments
If the infestation extends beyond the bathroom walls into the subfloor or foundation, a localized foam treatment won’t be enough. Two broader approaches are commonly used, often together.
Liquid termiticide barriers involve applying chemical to the soil around and beneath the structure. A trench is dug along the foundation, the termiticide is applied, and the soil is replaced. This creates a continuous treated zone that kills termites as they pass through it. Common active ingredients registered by the EPA for this use include fipronil, imidacloprid, bifenthrin, cypermethrin, and permethrin. Each works by disrupting the insect’s nervous system in slightly different ways. Liquid barriers cost $3 to $16 per linear foot.
Bait systems take a different approach. Stations containing slow-acting insect growth regulators are placed in the ground around the home’s perimeter. Termites feed on the bait and carry it back to the colony, where it inhibits development and gradually collapses the population. Active ingredients in bait systems include hexaflumuron (the first termiticide registered as a reduced-risk pesticide by the EPA) and noviflumuron, both of which disrupt termite growth rather than killing on contact. Bait systems cost $8 to $12 per linear foot and require ongoing monitoring, typically on a quarterly basis.
Borate Wood Treatments
Borates are commonly used as a preventive spray applied directly to exposed wood. They’re most practical during renovation or new construction, when wall framing and subfloor joists are accessible. If your bathroom termite problem requires tearing out damaged drywall or replacing rotted framing (which it often does), treating the new and remaining wood with a borate solution before closing the wall back up adds long-term protection. Borates penetrate the wood and make it toxic to termites that try to feed on it later.
What You Can Do Yourself vs. What Needs a Pro
Consumer-grade foam termiticides and borate sprays are available, and a small, clearly contained pocket of drywood termites in accessible wood trim can sometimes be handled as a DIY project. But bathrooms complicate things. The damage is often behind tile, inside wall cavities, or beneath the subfloor where you can’t see the full extent without opening things up. Subterranean termites are almost always a professional job because effective treatment requires reaching the soil beneath or around the foundation, and misapplying termiticide can leave gaps the colony exploits.
A professional inspection typically reveals whether the problem is limited to the bathroom or has spread to adjacent framing, which changes the treatment plan entirely. Subterranean infestations cost $225 to $900 on average to treat. Drywood termite treatments range from $225 to $2,500 depending on severity, with whole-structure fumigation (tenting) at the high end costing $5 to $20 per linear foot.
Fix the Moisture Problem or They’ll Come Back
No termite treatment in a bathroom will hold long-term if the conditions that attracted them remain. After treatment, address every moisture source. Repair leaking pipes and supply lines. Replace any caulk or grout that’s allowing water behind tile. Make sure your bathroom exhaust fan actually vents to the outside (many older homes vent into the attic, which just moves the moisture problem). Check the crawlspace beneath the bathroom for standing water or soil-to-wood contact, both of which invite subterranean termites back.
If the subfloor has been damaged, it needs to be replaced, not just treated. Termite-weakened wood loses its structural integrity, and layering new flooring over a compromised subfloor leads to sagging, cracking tile, and potential water damage that restarts the cycle.