Roof Soft Washing in Portland, ME

Roof soft washing is the low-pressure way to clean a roof, and on a shingle roof it is the only method we use. In a climate with about 47 inches of annual rain and frequent fog, north-facing roof planes and anything under trees stay damp long enough for dark streaks, lichen and thick moss to take hold. A soft wash applies a cleaning solution that kills and loosens that growth, then lets rain and a light rinse carry it off over the following days and weeks.

Why pressure washing a roof is a bad idea

The gritty surface on an asphalt shingle is a layer of mineral granules, and it is what protects the asphalt from UV. Pressure strips that grit away. HomeGuide reports that roofing contractors, the Roof Cleaning Institute of America and the Asphalt Roofing Manufacturers Association all recommend against using a pressure washer on shingle or tile roofs. Lost granules do not come back. High pressure can also force water up under shingle tabs and flashing. The only roofs where pressure washing makes sense are solid metal roofs, and even there we keep it moderate.

Moss is more than a look

Black streaks are mostly cosmetic. Moss is different: it holds water against the roof, lifts shingle edges as it grows, and sheds into gutters, where it clogs downspouts. We do not scrape or pry thick moss mats, which tears shingles. Instead we treat it, let it die back, and remove what loosens with gentle brushing or a light rinse. Thick mats sometimes take two rounds.

What different roofs need

• Asphalt shingles: soft wash only, with solution strength set for the amount of growth
• Cedar shakes and shingles: a wood-appropriate solution and a careful rinse; badly worn cedar may need a roofer instead
• Slate: low pressure only, with care around brittle or loose pieces
• Metal: moderate pressure is acceptable, though a soft wash is often enough

Safety and access

Many Portland houses are tall and steep, with dormers, chimneys and tight side yards. Much roof washing can be done from ladders and the eaves, keeping foot traffic on the shingles to a minimum. If a roof is too steep or fragile to work safely, we say so. We also look for missing or cracked shingles, lifted flashing and sagging gutters while we are up there and point them out, because washing is not a repair and a damaged roof should be fixed first.

Plants, gutters and runoff

Roof solution comes down through the gutters and downspouts, so we wet and cover plantings at the drip line, check where downspouts discharge, and rinse beds afterward. Downspouts that dump onto a driveway leading to the street are redirected to the lawn for the job.

Keeping it clean longer

Trimming overhanging branches lets the roof dry faster. Zinc or copper strips near the ridge release metal ions in the rain that slow regrowth; HomeGuide lists zinc strips at about $30 to $60 per 50-foot roll and moss prevention treatments at $100 to $250.