Buying an old Philadelphia rowhome: basement checklist

Why the basement deserves extra attention

Census data summarized by the Economy League of Greater Philadelphia show that roughly four in ten homes in the city were built before 1940. Many rowhomes and twins of that age stand on fieldstone, rubble or brick foundations laid in lime mortar, with no footing drain and no vapor barrier. Add a combined sewer system serving close to half the city’s area (Philadelphia Water Department) and party walls shared with neighbors, and the basement is where many surprises hide.

A damp basement is not automatically a deal-breaker – most can be fixed – but you want to know what you are buying and what it may cost.

Read the seller’s disclosure first

Pennsylvania requires sellers to complete a Seller’s Property Disclosure Statement. It asks directly whether the seller is aware of any water leakage, accumulation or dampness in the basement or crawl space, and about any repairs or other attempts to control water, including when and by whom (49 Pa. Code § 35.335a). Read those answers closely and ask for invoices and warranties for any waterproofing work – some warranties transfer to a new owner.

Walk-through checklist

Bring a flashlight and look for:

• Water stains, tide lines or rust at the base of walls, furnace, water heater and stored items
• White crust (efflorescence) or crumbling mortar on stone and brick walls
• Fresh paint or new paneling on only part of the basement – ask what it covers
• A musty smell, mold on wood or drywall, or a running dehumidifier
• A sump pit: is there a pump, does it have a lid, is there water in it?
• An existing interior drainage system (a gap or channel along the floor edge, a membrane on walls) – ask for the warranty
• Floor drains: signs of backups such as debris rings or stains around them
• Cracks in the floor slab or walls, bulging walls, sagging beams
• Outside: gutters and downspouts (including the neighbors’), cracked sidewalk joints along the front wall, rear areaway drains

Inspections worth ordering

• A general home inspection with a close look at the basement and moisture readings on the walls.
• A sewer scope (camera inspection of the line from the house to the street). Old clay or cast-iron laterals can be cracked or root-filled, and repairs are the owner’s responsibility. If the lateral is broken, the city’s HELP program offers zero-interest loans for repairs, according to the program information on phila.gov.
• A waterproofing contractor’s assessment if you see signs of water, so you have a scope and price before you settle.
• A structural engineer for bulging walls or significant cracks.

What repairs typically cost

Use quotes, not averages, when negotiating. Our detailed Philadelphia cost guide explains what drives the price in rowhomes.

After you buy

• Apply for the Basement Backup Protection Program if floor drains have backed up; the Philadelphia Water Department pays for backwater valve installation for eligible customers.
• Fix gutters, downspouts and the sidewalk joint along the front wall before tackling the inside.
• Talk to neighbors about shared problems – a neighbor’s downspout can flood your basement.
• Add water backup coverage to your homeowners policy; standard policies usually exclude sewer backups.
• Plan a lasting fix for seepage: interior drainage and a sump pump are the usual approach for stone basements.

Sources

• Economy League of Greater Philadelphia: Philadelphia housing (U.S. Census Bureau ACS data)
• Philadelphia Water Department: Green City, Clean Waters
• 49 Pa. Code § 35.335a: Seller property disclosure statement (Cornell LII)
• City of Philadelphia: Basement Backup Protection Program
• U.S. Inspect: Sewer scope inspection
• HomeAdvisor: Foundation or basement waterproofing costs in Philadelphia, PA
• Fixr: How much does it cost to waterproof a basement? (2026 data)
• This Old House: Sump pump cost
• NerdWallet: What is water backup coverage, and do you need it?