Roof Cleaning, Moss Removal, Moss Treatment

Roof cleaning and regular care are essential here in the Northwest. Due to a long overcast and rainy season, combined with all our beautiful trees, our roofs can take a beating over time. Moss, lichen, leaves, needles, and other debris not only serve to make a home look run-down, but they also trap moisture into shingles, which speed the buckling process, cause water damage and decay. Regular roof maintenance can delay the cost of an expensive re-shingling by years.

Depending on the situation, we use leaf-blowers, brushes, or pressure-washers to clean most types of roofs. This is often done in combination with a cleaning agent and/or moss prevention treatment.

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 Here are our four main roof care options:

Option A:  Routine Care

  • Air blow loose debris
  • Moss treatment
  • Gutter cleaning
  • Clean up debris from ground

While this option will not get rid of old dead moss, it is the easiest on your roof and budget. It is also the norm for routine roof cleaning. We air-blow the roof of any loose debris and apply the treatment (usually zinc sulfate monohydrate, powdered or sprayed, depending on roof type and weather) before cleaning out the gutters and our mess from the ground. If your roof has very thin moss or is just beginning to green, this is the way to go. Here in the northwest, we generally recommend doing this annually, or every other year, depending on the amount of sun your roof gets. Please note again: If you want us to remove any moss, this is not the option for you.

Roof cleaning

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Option B: Roof Brush

  • Brush removal of moss
  • Air blow
  • Moss treatment
  • Gutter cleaning
  • Clean up debris from ground

Roof cleaning by brush can be a good way to go in certain circumstances. We brush off the moss, air-blow the roof, lay down the zinc treatment (see description in Option A) to kill off any moss left behind, and clean up our mess. Though this won’t leave the roof quite as clean as Option C, it is often a very close second, requires no water, and can be less expensive.


Option C: Roof Wash

  • Air blow loose debris
  • Apply cleaning agent
  • Wash off moss
  • Apply moss treatment
  • Clean out gutters
  • Clean up debris from ground

For roof cleaning that gets the roof looking as new as possible, a roof wash may be the best way to go. We begin by blowing off the roof and cleaning out the gutters if needed. Then we spray the whole roof with an outdoor cleaning agent to loosen the moss and wash the whole roof with a low-pressure, high-volume pressure-washer. After clearing out the gutters and downspouts (again), we rinse any debris that might have splashed onto your siding, clean up the ground, and treat the roof to prevent moss from growing right back. The Option C is a favorite method for those who simply must have their roof looking as sharp as possible.

Roof Cleaning before and after

Option D: Soft Wash 

  • Air blow loose debris
  • Soak moss with outdoor cleaning agent
  • Gutter cleaning
  • Clean up debris from ground

Many roofers prefer the soft wash for roof cleaning. This involves a pre-cleaning: air blowing off the loose debris, cleaning out the gutters, and cleaning up any mess we’ve made from the ground. Then we return to the roof to completely soak it with an outdoor cleaning agent (e.g. 30-Seconds Outdoor Cleaner). While this method will not remove the moss, it does kill it completely and immediately. This method is best used on roofs with thick shingles or very steep pitches where a zinc treatment will be less effective.

Frequently Asked Questions about Roof Cleaning and Care:

What types of roofs do you clean?

We clean most roof types: composition, aluminum, cedar shake, torch-down, pvc, and many types of tile. There are a few exceptions, however. We don’t clean soft aluminum tiles for example, due to damage liability. We also don’t clean roofs we aren’t equipped to clean safely or roofs in need of replacement or serious repair. If you have any questions about our roof care options for your own roof, please contact us.

I’ve heard you should never use a pressure-washer washing for roof cleaning. Why does your company pressure-wash roofs?

It is a well-known fact that pressure washers can do a lot of damage. A high-volume, high-psi pressure washer can actually bore a hole right through concrete without much problem. Knowing this has rightfully made most homeowners wary about having anyone pressure-wash their roofs. And a lot of contractors, who know less about pressure washers than they do about the potential damage they can do, insist that a pressure washer should never be used on a roof. But to that we say, “abusus usum non tollit,” the abuse of something doesn’t negate its proper use. Just because knives pose a threat to small children, doesn’t mean we don’t keep a few in the house and use them for preparing meals. We all know about knives because we all use them. Not everyone, however, knows about pressure washers.

The truth is that a commercial pressure washer in the hands of a well-trained tech is often the softest and best approach to moss removal, especially where the only other alternative is to use a wire brush. Because there is so much misinformation about pressure washing roofs and too many “cowboys” out there with pressure washers, it might be useful here to share one piece of knowledge our techs have about washing roofs that most people and many contractors* don’t.

For example: You might know that the type of tip used at the end of a pressure washing wand is one of the essential components in determining the outcome of a project. And you might also know that pressure washers come with a set of tips of varying degrees, from 0° to 40° plus a rinse tip. But did you know that those tips are sized to match your specific machine? If you own a 4-gpm 4000psi machine, you will have a set of four tips labeled 0004, 1504, 2504, 4004. The first two digits in each of those numbers tell you the degree of the flow of water from those tips: 0°, 15°, 25°, and 40°, respectively. The last two digits tell you the size of the orifice. In this case, 04, for the 4 gallons per minute (gpm) of water your machine is designed to draw. Now, if you were to replace these tips with size 08 tips on this particular machine, your pressure would drop substantially while you would maintain the same flow rate. You would now have a 4gpm 1000psi machine. In our case, we ordinarily use 8 or 10gpm machines at 3000 psi for concrete, aggregate, and other hard surfaces. The tips we most often use are size 09 or 10 tips. When cleaning roofs, however, we use size 12, 15, or more, depending on the roof type and condition to drop the psi significantly and eliminate the potential for damage.

This may be more than you wanted to know. And there are many other things a well-trained technician knows about pressure washing such as where to hold the wand in relation to the surface, pre-soaking with cleaning agents, what types of other tools can be used, when not to pressure wash, to name a few. All our techs are well-trained, smart, and experienced in cleaning roofs. If we offer the Roof Wash as an option for your roof cleaning, it will be done carefully with minimal abrasion and the end result will be beautiful.

*In reality, many roofing contractors know that psi can be adjusted downward. They also know that a pressure washer in the hands of a well-trained tech is often preferable for roof cleaning to rubbing it over with a wire brush. But, since they have no idea who’s doing the roof cleaning, or what kind of training they might have, they often simply recommend against pressure washing roofs for anyone except themselves.

How often should I have roof washed?

The best option for the life of your roof, whatever type, is to never wash it (or brush it, for that matter), but to maintain it regularly by blowing off the debris and treating the moss. However, this might not cut it for aesthetic preferences, especially if maintenance has been long-neglected. Aluminum, rubber tile (faux slate), and thick concrete tile may be washed every few years as needed without causing leaking or reducing the life of the roof. And those who simply must have their composition roof looking completely new in a very short period of time (e.g., the house is going on the market), washing may be the best option. If you have questions about your own situation, please don’t hesitate to ask one of our techs.

Do you clean with air-compression?

We use air-blowers (leaf-blowers) to remove loose debris from roofs, and we use high-volume, low-pressure pressure washers for more thorough roof cleaning, but we don’t use compressed air. We want to provide excellent service to our customers and haven’t been convinced that air-compression cleaning does a great job. Unlike water, compressed-air leaves a lot of dirt behind, yet it is still hard on the roof. If a roof must be cleaned and made to look like new, pressurized water in the hands of an experienced tech is the way to go. If routine leaf/debris removal is required for roof cleaning, a top-of-the-line commercial backpack blower is all that’s needed to get the job done.