Philadelphia's combined sewer system, dating partly to the late 19th century, regularly surcharges during heavy rain, forcing sewage backward into basements through floor drains. Summer relative humidity averages above 65%, and Hurricane Ida in 2021 caused over $100 million in insured losses in the metro — making fast response critical.
Sewage backup — IICRC Category 3 — is Philadelphia's most serious water damage scenario and requires full demolition of all porous materials in contact with the water. In rowhouses with shared masonry walls, moisture migrates laterally, often saturating adjacent units before the source homeowner detects any staining.
Pre-1978 properties require a contractor with EPA Renovation, Repair, and Painting (RRP) certification before any demolition proceeds. Ask your contractor for their RRP cert, and add a sewer backup endorsement to your homeowners policy before a loss — it typically costs $50 to $150 per year.