San Francisco's marine layer fog brings moisture and salt into contact with exterior surfaces daily. Salt is hygroscopic, meaning it absorbs water from the air. When salt deposits accumulate on siding, window frames, or roof flashing, they pull moisture into the material. This moisture then migrates through walls via capillary action and vapor diffusion, wetting insulation and drywall from the inside out. Paint loses adhesion. Wallpaper delaminates. This cycle is worst in western neighborhoods like the Outer Sunset, where fog exposure is heaviest, and in areas near the Presidio and Golden Gate Park, where wind-driven salt spray reaches blocks inland.
San Francisco's building stock includes thousands of Victorians, Edwardians, and early 20th-century homes built before modern moisture management systems existed. These homes lack vapor barriers, rely on gravity drainage instead of positive drainage planes, and use materials like wood siding and plaster that are vulnerable to moisture intrusion. Understanding how these older systems fail and how to repair them without destroying historic character requires local experience. We work with San Francisco homes daily and understand the building methods used in different eras and neighborhoods. That expertise prevents costly mistakes and ensures repairs last.
