We live in a NW climate with lots of rain, moss, and slugs. Our neighbors had some guy pressure wash the moss off of their roof. Took him all day.
Is it safe to do that? Our light colored composition shingle roof is 16 years old and has too much moss to scrape off. Some of it grows underneath the edges of the shingles. It seems like pressure washing would remove a lot of the tile/sand granules. Our neighbors roof looks great from across the street at least.
[quote=“Cingent”]We live in a NW climate with lots of rain, moss, and slugs. Our neighbors had some guy pressure wash the moss off of their roof. Took him all day.
Is it safe to do that? Our light colored composition shingle roof is 16 years old and has too much moss to scrape off. Some of it grows underneath the edges of the shingles. It seems like pressure washing would remove a lot of the tile/sand granules. Our neighbors roof looks great from across the street at least.[/quote]
I would not use a pressure washer on a roof, period.
You can try a broom or plastic scraper (be careful) or there are some chemicals that will work as well. And as far as your neighbors house looking good from across the street, that’s sort of a tradesman joke, “It’ll look great when I get home”. Maybe see if any local companies have some better method than pressure washing.
I agree with BC. I live in Seattle. Lots of moss. Broom off the large stuff as able from top down, careful as slick to walk. Go to Lowes or Feddies, etc. and get Moss be gone. Follow directions and let it do the work.
If you power wash a roof you need to be extremely careful not to use too much pressure.
It is very tempting to use just a little more pressure because just a little more works a lot better…
The problem is that with too much pressure you are removing the granules.
You need the granules to protect the roof from the sun, that is the primary purpose of the granules.
After a good power washing the roof will look great but if too much pressure is used a significant chunk of the roofs life has just been removed, it looks better though…
So IMO using a power washer on a roof is a big no no, people still do it though and the customer is happy because they don’t know that their roof was damaged by the power washing.
The damage is not immediately obvious.
A roof can be power washed as long as the correct tip is being used along with no direct high pressure.(As its already been stated)
I have seen what happens to a roof when a improper tip and high pressure is used and its nothing short of brutality to any roof system. It removes and cleans alright,It removes every granule on the shingle,blows out the matting and leaves a squeaky clean surface right down to the roof deck.(Experience bites)
Listen to everyone who posted here…do not pressure wash your roof.
Like Rickengie…I do the sweep (as well as a flat bare to scrap the tough moss that a broom does not get) and then use the moss-be-gone powder a day before the forecasted rain.
You have a 16 yr old roof with losts of moss. If you can afford it (especially if you have existing 3-tab on your roof—almost to the end of its life!) re-place your roof. If you cannot afford it…find a contractor who will perform the reccomendations I or others have posted here. Ignore the pressure washing…even if they say they will use the correct tip. Using the correct tip and getting too close to the shingle will damage it anyways.
ATTENTION ALL HOMEOWNERS - ROOF CLEANING
There are options:
1. Get up on your roof and clean your roof.
The problem:
The first to think about is safety. Water / heights / pressure / Hoses-are major tripping hazards /wet and slippery moss / soapy solutions / Spray wand kickback.
There is no more dangerous place on your property than on your roof. In addition to the normal dangers of being on the roof, the addition of water, especially on roofs with mold or algae, makes the roof slippery and even more dangerous than it would be under normal conditions. If you fall off your roof while cleaning or working on your roof…your homeowners insurance will not pay for your medical costs.
**2. Spray from the ground **
The problem:
Roofing materials are designed to shed water that is falling from above. When you spray from below you are spraying water up under the roofing materials and this creates the potential to lift and damage the shingles as well as drive water under them creating leaks.
Another problem when it comes to spraying from the ground is what type of solution you are going to use. It would have to be an extremely strong solution to even begin to work at all.
Pressure Washer - You see all over the web there are some huge arguments about using a pressure washer to clean your roof. Well, what is the pressure at? You can have a pressure washer
set to spray like a water fountain. You can also have one set so high you can permanently etch your name on the sidewalk. We operate in Erie, PA. We have seen homeowners watch us and pull out there pressure washing machine and start blasting and ruining their shingles. Not realizing we are using a low pressure-high volume rinsing machine. There are 2 solutions applied before we even bring the machine out. What you see is not always what you think you are seeing. Here is a video of Brink Kanga roof in Erie, PA using a three step spray solution roof cleaning process and a high volume low pressure rinse. Erie Roof Stain and Algae Removal Video
HUGE VARIABLE - What shape are the shingles in. Water being sprayed on a roof that is 2yrs. old vs. 18 yrs. old is a huge difference. Not all roofs are the same. Shingles age and deteriorate.
There are so many variables. It is just like the argument about zinc strips. Do they work?
Well how old was the roof they were installed on. Was the roof cleaned before they were installed?
What solution was used before the zinc strips were installed. Was there a protectant spray used before they were installed. What type of zinc strip is being used. What brand? What percentage of the product is actually zinc? How much of the zinc strip is shoved up under the shingle and how much is actually going to get rained on.
I am an owner of Brink Kanga Roof in Erie, PA and we offer roof stain removal / roof algae removal / roof moss removal / and roof stain prevention and maintenance. I think that the word “Cleaning” in roof cleaning makes the whole process seem easier than what it really is.
There are workers at Brink Kanga Roof that have been roofing for 10+ years and I still wouldn’t tell them to get up on a roof and go through the cleaning process without first training them specifically in the dangers of roof cleaning. There are different safety variables to be taken in consideration.
Getting back to the question and answer. Don’t use a pressure washer. Don’t waste your time researching for weeks how to clean it properly. Call someone that is a professional roof cleaner. Ask to see their insurance. Review your contract. Review the warranty given. Then go spend the hrs. doing something fun like going to eat with your family or friends or go to an amusement park and ride on the biggest roller coaster there is…wait, you’re saying you won’t go on the biggest roller coaster in the world…but you were considering climbing up on your roof and spraying water and solution all over etc. …Think about it? Stick to the coaster. 
Just teasing, but seriously don’t risk your lives homeowners. There are a lot of roofers including myself that have witnessed a friend / worker that had 20+yrs. experience fall to their death roofing. Roofing can and will kill you. I mean it literally. http://www.blackroofstains.com
Like onarooftop said, you want a low pressure/high volume roof wash. We use a proprietary agent called American Roof Brite. Keep in mind that this is work for professionals and not every roof situation is a good candidate for this process.
Any professional roofer can use a power washer. Just not for the average Joe. Better to just say no unless it is the pro who is going to do the work. Removes the blame game for the inexperienced.
You don’t ever power wash a roof. You Soft-Wash a roof. Power washing takes 5 years off the roof surface. We apply a special blend of soaps and let the rain rinse it off. It can take up to 4 to 6 weeks for the moss to come off the roof. There will be some granule loss under the moss and lichen. But that is normal.
I agree with using the correct tip and going slow and steady.Roof cleaning can be tough i would go with soft washing it.
Squeaky Clean
Never power wash roof shingles. No manufacturer recommends that. Our company is celebrating 100 years in 2023. www.rexroofinginc.com website 1st page scroll down to Copper
Cat Strips info. Only product that works against moss. Algae resistant shingles only work against black algae discoloration. Only Atlas with Scotchguard has lifetime protection. Ventilation helps keep the attic dry, but still may not address moss.