Pressure washing costs in Portland

Moss is part of owning a roof in Portland. Oregon State University Extension calls it inevitable in the Pacific Northwest, where seasonal rain keeps it thriving. The moss itself doesn't directly damage the shingles, it says. It holds soil, debris and moisture against them, and on an asphalt roof it can lift shingles and let water reach the layers below.

Getting it off takes a light hand. OSU Extension says experienced users may pressure-wash, but poor technique can damage shingles, and when in doubt a long-handled scrub brush is the safer tool. Clean the roof first, then treat. Zinc sulfate is one of the treatments it names, but not on a house with copper gutters, downspouts or flashing, because zinc corrodes copper. The long-term fix is trimming trees so more sun reaches the roof.

What you rinse off has rules too. Portland's Bureau of Environmental Services lists wash water from cleaning pavement or buildings among the things City Code 17.39 keeps out of storm drains. Send it onto a lawn or unpaved part of your property where it won't reach the street, or pour it into a sanitary drain on your property. A plain rinse of your siding is the exception, as long as no soap, chemicals, steam or heated water go into it.

Portland requires mobile power washing businesses to hold a Mobile Washer Discharge Authorization, and under it the washing happens on your property, never in the right-of-way, with the water contained on site.