Philadelphia termite and WDI inspection guide: wood-destroying insects, treatment options, and what buyers need to know

Philadelphia's pre-war rowhouse stock sits on wood floor joists, subfloor, rim joists, and stair stringers that have been in contact with or in close proximity to soil for 80 to 140 years. That combination of wood, soil contact, age, and urban density creates a meaningful wood-destroying insect risk profile that every buyer in this market should understand before the inspection contingency expires. Subterranean termites, carpenter ants, and powder post beetles are all documented in Philadelphia's pre-war housing stock, and the damage they cause ranges from minor and easily treated to structurally significant and expensive to repair.

This guide covers what a Wood-Destroying Insect (WDI) inspection is, what the NPMA-33 report tells you, what insects are present in Philadelphia rowhouses and how to identify them, how FHA and VA loans treat WDI findings, treatment types and costs, structural damage repair scope, and an 8-item buyer checklist for managing WDI findings within an inspection contingency.

What a WDI inspection is and what it costs

A Wood-Destroying Insect (WDI) inspection is a formal inspection performed by a licensed Pennsylvania pest control operator (PCO) that evaluates a property for evidence of wood-destroying insects. It is distinct from a general pest inspection: a WDI inspection focuses specifically on insects that destroy wood structure, and it results in a standardized form (NPMA-33, the Wood-Destroying Insect Inspection Report) recognized by mortgage lenders.

• Form NPMA-33. The NPMA-33 is the nationally standardized WDI inspection report form. It identifies whether visible evidence of wood-destroying insects (active or inactive), evidence of previous infestation, or evidence of previous treatment was found in accessible areas of the property on the inspection date. The form distinguishes between four insect categories: subterranean termites, drywood termites, carpenter ants, and wood-boring beetles.
• Licensed inspector requirement in Pennsylvania. In Pennsylvania, WDI inspections must be performed by a licensed pest management professional. General home inspectors are not licensed to perform WDI inspections unless they also hold a Pennsylvania pest control license. Order a WDI from a licensed PCO separately from your general home inspection.
• When lenders require it. FHA and VA loans require a WDI inspection (on NPMA-33) on all transactions where there is evidence of or concern about wood-destroying insects, and VA requires it on all purchase transactions (except condominiums) regardless of visible evidence. Conventional lenders vary: Fannie Mae and Freddie Mac do not require WDI by default, but individual lenders may require it if the appraiser notes concerns or if the property is in a high-termite-risk area.
• Cost. WDI inspections from licensed Pennsylvania PCOs in Philadelphia typically run $75 to $175. The inspection should be ordered and completed within the inspection contingency period so that any findings can be addressed before the contingency deadline.
• Timing. Order the WDI inspection at the same time as your general home inspection, so both are complete well before the inspection contingency deadline. If a WDI inspection reveals active infestation, you will need time to get a treatment bid and potentially a structural repair estimate before responding.

Wood-destroying insects in Philadelphia rowhouses

Four types of wood-destroying insects are documented in Philadelphia's housing stock. Their identification, behavior, and infestation patterns differ, and each requires a different response.

Insect	Prevalence in Philadelphia	Behavior	Key Indicators
Subterranean Termites	Most common; present throughout the metro area	Live in soil colonies; enter structures through soil contact, foundation cracks, and mortar joint gaps; consume wood cellulose; build mud tubes for above-ground travel	Mud tubes on foundation walls, floor joists, and utility penetrations; hollow-sounding or damaged wood; swarmer wings near windows in March to May
Drywood Termites	Less common; more typical in southern climates but documented in Philadelphia	Live inside the wood they infest (no soil contact needed); found in wood framing and furniture; smaller colonies than subterranean	Pellet-shaped frass (fecal pellets) near infested wood; no mud tubes; exit holes in wood surface
Carpenter Ants	Common; active primarily April through September	Do not eat wood; excavate galleries in soft or moisture-damaged wood for nesting; indicate an underlying moisture problem in the structure	Sawdust-like frass mixed with insect parts (legs, wings) near active galleries; large black or bi-colored ants (1/4 to 1/2 inch); galleries that run across wood grain (unlike termites which follow grain)
Powder Post Beetles	Common in pre-war rowhouses with hardwood flooring and antique furniture	Larvae bore through hardwood; adults emerge through small round exit holes; can remain dormant for years in dry conditions	Fine talcum-like powder frass near or below infested wood; small round exit holes 1/16 to 1/8 inch diameter in hardwood floors, trim, and furniture; common in pre-war hardwood flooring

Rowhouse-specific termite risk factors

Philadelphia's pre-war rowhouses have structural characteristics that create elevated subterranean termite risk compared to newer construction or detached homes. Understanding these risk factors helps you know where to look and what to ask during the inspection.

• Wood floor joists near soil grade. Pre-war rowhouses built between 1880 and 1940 typically have wood floor joists, subfloor, rim joists, and stair stringers in the basement or lowest level. Subterranean termites enter from soil, and in pre-war construction the distance between soil grade and the lowest wood members is often minimal. Foundation wall cracks, mortar joint gaps, and pier gaps provide direct pathways from soil to wood.
• Party wall penetrations. Shared party walls between attached rowhouses have penetrations for utility lines, sewer laterals, and historic structural connections. These gaps and penetrations create movement pathways for termites between adjacent properties. A termite colony in a neighboring property can enter your property through shared wall penetrations without any visible evidence on the exterior of your unit.
• Dirt floors and sump pits in pre-war basements. Many pre-war rowhouses have basement sections with exposed soil floors or sump pits that expose soil directly to basement air. Exposed soil in the basement dramatically shortens the path for subterranean termites from colony to wood structure. Any property with a dirt-floor basement area should be considered elevated risk.
• Wood-to-soil contact at rear additions. Rear additions, porch structures, and exterior wood steps commonly have direct wood-to-soil contact, particularly in older properties where additions were built informally without current code requirements for wood separation from grade. These are common termite entry points.
• Moisture conditions. Plumbing leaks, basement seepage, flat roof drainage failures, and poor site drainage create chronic moisture conditions that soften wood and make it more susceptible to both termite infestation and carpenter ant colonization. Moisture is both a risk amplifier for WDI infestation and an independent damage condition that should be addressed regardless of insect findings. See our Philadelphia basement waterproofing guide.
• Swarming season in Philadelphia. Subterranean termite swarming season in the Philadelphia metro runs from late March through May, with peak activity in April. Swarmer termites (reproductive winged termites) emerge from established colonies to start new colonies. Finding swarmer wings on interior windowsills or floor areas in spring is a strong indicator of an active colony in or adjacent to the structure.

Identifying termite damage and active infestation

Knowing how to recognize termite activity before the inspection -- and knowing what to look for when your inspector is in the basement -- puts you in a better position to ask the right questions and understand the findings.

• Mud tubes on foundation walls and floor joists. Subterranean termites build pencil-width mud tubes to travel from soil to wood above grade. These tubes are the most reliable visible indicator of subterranean termite activity. Inspect foundation walls, floor joists near the foundation wall, sill plates, utility penetrations, and piers with a flashlight. Fresh mud tubes are soft; dried tubes may be historical rather than active (though a PCO can assess whether tubes appear active).
• Hollow-sounding or soft wood. Termites consume wood from the inside out, leaving a thin shell of surface wood while hollowing out the interior. Tap wood members with a screwdriver handle and listen for a hollow sound. Probe suspect areas gently with the tip of a screwdriver: wood that crumbles, collapses, or feels soft indicates active or past infestation. This probing technique is standard in WDI inspections.
• Termite galleries vs. carpenter ant galleries. Termite galleries run parallel to the wood grain, with mud deposits within the gallery. Carpenter ant galleries run across the wood grain and have a clean, smooth appearance without mud. Distinguishing between the two is important because they indicate different problems: termites indicate active or prior insect consumption, while carpenter ants indicate a moisture-damaged wood area that attracted nesting.
• Swarmer wings near windows and floors. Wings shed by swarmer termites in spring are a clear sign of an established colony nearby. Look near windowsills, along baseboards, and in basement corners. Swarmer wings from termites are all the same length (unlike ant wings, where the front pair is larger than the rear pair).
• Evidence of prior treatment. Look for Sentricon bait stations embedded in the soil perimeter, Termimesh stainless steel mesh screens at foundation penetrations, or drill marks in the concrete slab near the foundation wall perimeter (indicating prior liquid termiticide injection). Prior treatment evidence does not mean the property is currently protected; treatment warranties expire and colonies can re-establish after protection lapses.

Treatment types and costs

Not all WDI treatment is the same. The appropriate treatment depends on the insect type, the extent of infestation, and the construction characteristics of the property. Get a treatment bid from a licensed Pennsylvania PCO within the inspection contingency period, so you have documented cost data to use in negotiating with the seller.

Treatment Type	Typical Cost (Philadelphia)	Description	Notes
Liquid termiticide perimeter treatment	$500–$1,500	Drilling through concrete slab or foundation perimeter and injecting termiticide barrier in soil; creates a chemical barrier between soil colony and structure	Retreatment every 5 to 10 years; requires drilling and patching of slab or foundation perimeter; effective against subterranean termites
Bait system (Sentricon)	$1,200–$2,500 install + $300–$500/year monitoring	Bait stations placed every 10 feet around soil perimeter; termites find and feed on bait and carry it back to colony; colony eliminated over 3 to 6 months	Requires annual monitoring contract; colony elimination is slower than liquid treatment; does not require drilling in most applications
Borate wood treatment	$800–$2,000	Borate solution applied directly to exposed wood in basement and crawl space; absorbed into wood and kills insects that consume treated wood	Prevents future infestation in treated wood; not suitable for active infestations as primary treatment; effective for powder post beetles and as a preventive measure
Fumigation (drywood termites)	$2,000–$8,000	Tent fumigation with Vikane gas (sulfuryl fluoride); entire structure sealed and fumigated; kills all drywood termites throughout structure	Required for drywood termite infestations; not effective against subterranean termites; licensed fumigators are less common in Philadelphia than in southern markets; requires vacating property for 2 to 3 days
Spot treatment	$200–$600	Targeted injection at isolated infestation area; foam or liquid termiticide injected directly at the infestation site	Appropriate only for very limited or early-stage isolated infestations; not appropriate for widespread subterranean termite colonies that may extend beyond the treated area

Carpenter ant treatment and the moisture problem

Carpenter ants are the second most common WDI finding in Philadelphia rowhouse inspections. Unlike termites, carpenter ants do not consume wood for nutrition. They excavate galleries in soft or moisture-damaged wood to create nesting spaces. A carpenter ant infestation is almost always a sign of an underlying moisture condition that has softened wood in the structure and made it attractive for nesting.

• Identification. Carpenter ants are large (1/4 to 1/2 inch), black or bi-colored (black body with reddish thorax), and may be winged (swarmers) or wingless (workers). The frass from carpenter ant galleries looks like coarse sawdust mixed with insect body parts (legs, antennae, fragments), distinguishing it from termite frass which contains mud, and from powder post beetle frass which is very fine and talcum-like.
• Treatment. Exterior perimeter spray combined with interior crack-and-crevice injection typically costs $300 to $700 for a one-time treatment. Annual monitoring contracts run $150 to $300. Treatment kills the carpenter ant population but does not eliminate the moisture condition that attracted them.
• Address the moisture source. Every carpenter ant infestation should prompt a search for the moisture source. Common sources in Philadelphia rowhouses include: plumbing leaks at drain connections behind walls, roof infiltration through failed flat roof membranes or flashings, basement seepage from foundation wall cracks, and condensation from inadequate attic ventilation. Treating the carpenter ants without fixing the moisture source means the infestation will recur. See our Philadelphia mold guide and Philadelphia plumbing guide for related issues.
• Structural implication. The wood that carpenter ants choose for nesting is typically already soft and compromised by moisture. Any area with active carpenter ant galleries should be probed for wood rot and assessed for structural adequacy. What presents as a pest problem on the NPMA-33 may also represent a structural condition requiring repair.

Powder post beetle identification and treatment

Powder post beetles are common in Philadelphia's pre-war rowhouse stock, particularly in properties with original hardwood floors, antique trim, and older furniture. The larvae bore through hardwood, consuming the wood and leaving a fine powder-like frass as evidence of their activity.

• Identification. The key indicators are fine talcum-powder-like frass near or below suspect wood (often appearing as small piles or dusting on surfaces below), and small round exit holes in hardwood floors, trim, and furniture, ranging from 1/16 to 1/8 inch in diameter. The frass from powder post beetles is much finer than carpenter ant frass and does not contain insect parts.
• Old inactive infestations. In pre-war rowhouses, it is very common to find old exit holes and frass in hardwood floors and trim that represent historical infestations that are no longer active. An inactive infestation in dry conditions may not require treatment. A licensed PCO can assess whether an infestation is active (fresh frass, soft wood near holes) or historical (hard wood, discolored frass). Don't negotiate on cosmetic historical infestation that required no treatment; focus on active infestations.
• Treatment. Active powder post beetle infestations in exposed wood are treated with borate application to the affected wood surfaces, typically costing $500 to $1,500 depending on the extent of the affected area. Surface finishes (polyurethane, varnish) on hardwood floors may need to be removed to allow borate penetration. In severe cases, replacement of infested wood members is required.
• Furniture and antiques. Powder post beetles are also common in antique furniture and can spread from infested furniture to structural wood. For buyers purchasing a property that includes the seller's furniture, note that infested furniture should not be brought into a new home without treatment.

WDI report requirements in real estate transactions

The WDI inspection requirements differ by loan type. Understanding what your lender requires and what the findings mean for your transaction saves time and avoids surprises during the mortgage process.

Transaction Type	WDI Requirement	Treatment Requirements
FHA loan	WDI inspection on NPMA-33 required when the appraiser notes evidence of infestation; in practice often required in pre-war markets as a matter of lender policy	Any evidence of active infestation is a required repair before closing; appraiser must note visible evidence of infestation; lender will not fund until re-inspection confirms treatment and no active infestation
VA loan	WDI inspection required on all VA purchase transactions except condominiums; required regardless of whether visible evidence of infestation exists	Active infestation is a required repair before closing; evidence of previous infestation must be disclosed and assessed; VA appraiser guidelines require treatment completion and re-inspection before loan funding
Conventional loan (Fannie Mae / Freddie Mac)	Not required by Fannie or Freddie guidelines by default; individual lender may require if appraiser notes concerns or if property is in a designated high-risk area	Lender-specific; if required, treatment and re-inspection typically follow the same framework as FHA
Cash purchase	Buyer's discretion; no lender requirement	Strongly recommended in pre-war Philadelphia properties, particularly in high-risk neighborhoods with dense pre-war masonry rowhouses; all-cash buyers often skip WDI and regret it post-closing

Negotiating WDI findings during the inspection contingency

A WDI inspection finding gives you a documented basis for negotiation within the inspection contingency period. How you negotiate depends on what was found and the scope of any associated structural damage.

• Active infestation without structural damage. The most common negotiating outcome is seller-pays-treatment. Request that the seller engage a licensed Pennsylvania PCO to treat the infestation before closing and provide a treatment warranty transferable to the buyer. Get your own independent treatment cost estimate to verify the scope of the seller's proposed remediation. For FHA and VA loans, seller must treat before closing regardless of the negotiation.
• Buyer credit at closing. If the seller prefers not to manage the treatment themselves, a credit at closing equal to the documented treatment cost (with a reasonable contingency for additional findings once treatment begins) is an acceptable alternative. Use a documented PCO bid as the basis for the credit amount.
• Structural damage present. If the WDI report or the general home inspection identifies structural damage associated with infestation (compromised joists, damaged subfloor, degraded rim joists), negotiate separately for structural repair costs. Get a licensed contractor estimate for the structural repair scope before responding to the inspection. The treatment cost and the structural repair cost are separate line items in the negotiation.
• Prior treatment records. Request prior treatment records from the seller before your inspection. If the property was previously treated, ask for the treatment documentation, warranty, and the date of the last PCO re-inspection. A property with documented treatment under an active warranty is in a different risk category than one with no treatment history.
• Walking away. If the structural damage is extensive and the repair scope is unclear, or if the seller is unwilling to treat or credit, walking away may be the appropriate outcome. FHA and VA buyers in particular may have limited ability to close on a property with active infestation without lender-required remediation, which the seller must agree to finance.

Structural damage repair scope and costs

WDI damage to structural wood members in a Philadelphia rowhouse can range from minor section loss requiring sistering to extensive damage requiring full floor system replacement. Any structural damage assessment should involve a licensed contractor and, for damage to load-bearing members, a structural engineer. See our Philadelphia structural inspection guide for the full structural framework.

• Floor joist sistering. Sistering a damaged joist involves fastening a new full-length joist alongside the damaged one. For isolated joist damage in an accessible basement, sistering typically costs $200 to $600 per joist, including labor. If access requires removing finished ceiling from below, costs increase significantly.
• Full floor joist replacement. In cases of widespread termite damage across multiple joists in a basement span, full replacement of the affected floor system may be required. Full floor joist replacement for a typical basement span in a Philadelphia rowhouse runs $4,000 to $12,000 depending on span, joist count, and access.
• Rim joist replacement. The rim joist (the perimeter joist at the foundation wall) is a common location for subterranean termite damage because of its proximity to soil. Rim joist replacement runs $800 to $2,500 depending on length and access.
• Subfloor replacement. If termite damage has progressed from the joists into the subfloor, replacement of the affected subfloor area is required. Subfloor replacement runs $2,000 to $6,000 per room depending on subfloor type, joist spacing, and whether finished flooring above must also be removed.
• Stair stringer replacement. Stair stringers (the diagonal support members of stairways) are sometimes targets for subterranean termites entering from basement soil. Stair stringer replacement runs $1,000 to $2,500 per stringer. If all three stringers on a typical stair are damaged, total replacement cost can reach $3,000 to $7,500.
• Structural engineering assessment. For any damage involving load-bearing members, order a structural engineer assessment before finalizing the repair scope. A structural engineer can confirm whether the damage is localized or systemic, specify the repair method, and provide documentation that the repair meets current structural standards. Structural engineer inspections in Philadelphia typically run $600 to $1,500. See our Philadelphia home inspection guide for additional context.

8-Item Buyer WDI Checklist