It depends on what you care about most. Do you care about your roof warranty? If so, you must not pressure wash it. If your roofing fails due to manufacturer defects and you start a warranty claim they will send out an adjuster who is specifically trained on and instructed to look for signs of pressure washing. If they find signs, your warranty is void. Likewise, many roofing contractors will not honor workmanship warranties if a roof has been pressure washed, as it can disturb and prematurely degrade workmanship.
Do you have a metal roof? Do you mostly care about curb appeal? Then pressure washing may be the way to go, as it removes all of the dirt, grim, and most of the algae staining. If you choose to have your roof cleaned with pressurized water, you should hire a vetted professional with a solid portfolio with clear pictures of final products. Be careful with this one.
Home inspectors, roofing manufacturers, and many roofing contractors will tell you that all methods of mechanically removing moss is damaging and should be avoided. That includes scraping and brushing with abrasive brushes. Mechanically removing moss inevitably removes granules from the shingles.
The most gentle way to remove moss is to treat the moss with a moss killer, wait for the moss to die, and either let the rain rinse it into the gutters, blow it off with a leaf blower, or gently brush the moss off with a push broom.
We like the last method mentioned for traditional asphalt shingle roofs. It takes two days, but it is the easiest on the roof. On day one we come out and apply a zinc treatment to the roof. In the rainy seasons we apply a powder directly to the highest points on the roof and let the rain spread it around. In the dry seasons we apply the zinc treatment as a solution, so the wind doesn't blow the powder away and so you don't have unsightly white powder all over your roof.
On day two (2 to 3 weeks after) we blow, brush, rinse, or use a combination of the former to remove the dead brown moss. If there is still green moss on the roof, we need to apply another treatment and wait for it to die. Sometimes this can take a month but you can be assured that we will not void any warranties or excessively damage your roof.
We clean the gutters out completely and move all of the moss either into the woods/bushes on site, your yard waste bin, or haul it away.
Preventing it from growing. We offer maintenance plans that will prevent or prolong you from needing mechanical cleaning. Our maintenance plans are extensive and thorough. We will keep the moss at bay and make sure you don't have any other roof issues. In the next section you will learn all about our maintenance plan.