Power washing a cedar shake roof sent water into the attic: what owners should check

The owner wrote on Reddit's r/Roofing that the cleaning, repairs and treatment cost about a third of the price of a new roof. Keeping shakes clean matters: the Cedar Shake & Shingle Bureau (CSSB) recommends having a professional clear needles, leaves and moss, which hold moisture against the wood. On pressure washing the bureau is cautious. In guidance reprinted by a restoration contractor, it calls power washing the most contested topic in shake care, warns that inexperienced crews do significant damage, and wants each roof judged on its own for pressure, flow, nozzle distance and tip size.

Water inside is a known failure. A Cleaner Times guide for washing contractors says never to spray up and under shakes, because the water can end up in the attic or staining ceilings, and the spray can crack or loosen shakes. Soft-wash contractors quoted in the same guide rinse cedar at under 100 psi.

What to check now: get into the attic and look for wet or matted insulation, damp sheathing and framing around the vent, and stains on the drywall below. The U.S. EPA says water-damaged materials should be dried within 24 to 48 hours to prevent mold, and porous materials that turn moldy may have to be thrown out. If mold covers more than about 10 square feet, the EPA points owners to its professional remediation guidance. Photograph the damage before anything is moved.

Then put the claim to the contractor in writing: the uncovered vent, any shakes cracked or lifted by the wash, wet insulation and drying the attic. Check the treatment, too. The CSSB says a power-washed roof should get a topical treatment afterward, and it rejects any product sold as a sealant or waterproofer, because sealing locks in moisture that cedar needs to release.