What pressure washing does to asphalt shingles
Pressure washing strips the granules off asphalt shingles. Those little stone granules aren't decoration: they're the shingle's sunscreen and armor, protecting the asphalt underneath from UV and weather. Blast them off and you've fast-forwarded years of wear in an afternoon.
High pressure also drives water up under the shingle courses, breaks the adhesive seal between shingles, and can loosen flashing. The roof looks clean from the driveway. Up close, it just aged a decade.
It can void your warranty too
Shingle manufacturers are clear on this: damage from improper maintenance, including high-pressure washing, isn't covered. As a CertainTeed Certified contractor we install roofs to manufacturer spec, and we maintain them the same way. A pressure-washed roof can lose warranty protection exactly when you'd want it most.
What safe roof cleaning looks like
Safe asphalt roof cleaning is hands and air, not blasting: scraping and soft-brushing the moss off (working with the shingles, not against them), blowing the roof and valleys clear, then applying a treatment that kills the remaining moss so it releases on its own.
It's slower than pressure washing. That's kind of the point. The goal is a roof that's clean and still has all its granules.
If your roof is due, here's what our cleaning service includes. And for everything else moss-related, the Moss Handbook has you covered.
What about 'soft washing'?
Done right, soft washing (low pressure plus a cleaning solution) can be appropriate for some surfaces, and some reputable companies do good work with it. Our position for asphalt shingles in our climate is simpler: mechanical removal plus treatment gets excellent results with zero risk to the granules, so that's what we do.
Whoever you hire, ask one question: 'what PSI touches my shingles?' If the answer is a pressure-washer number or a blank stare, keep looking.