San Francisco's coastal neighborhoods frequently exceed 85% relative humidity on summer mornings, making open-air drying useless after a water loss. Approximately 60% of the city's housing was built before 1960, leaving original galvanized supply lines and cast-iron drains prone to sudden failure. Every hour without extraction adds structural loss.
The most common losses involve Victorian balloon-frame construction, where water migrates vertically inside wall cavities before staining appears. The city's combined sewer system — portions dating to the late 1800s — generates Category 3 sewage backups during heavy rainfall across neighborhoods from the Tenderloin to the Excelsior.
California requires contractor licensing through the CSLB. Confirm your restoration crew holds IICRC S500 certification and provides daily psychrometric drying logs. For sewage-category losses, verify antimicrobial treatment documentation. Request a full clearance report before reconstruction begins.