You have to be careful determining the method you want to use. As a homeowner or contractor I will explain the best way to make moss on roof surfaces disappear. This method will work on most roof types including asphalt shingled roofs. Asphalt shingled roofs are the most popular covering about 80% of homes. I’m a firm believer in following manufactures directions/recommendations. Following the directions for most asphalt shingled roofs for moss removal is how I found this great process. The Asphalt Roofing Manufactures Association represents the leading manufactures of roofs and they recommend this method as the only way to clean moss from roofs.
Moss roots itself into the roof surface as it grows. If you instantly remove the moss, you will damage the roof surface. The root of the moss will pull the top layer of granular from the surface. This is the first barrier of your roof. Compromising this barrier can result in rapid granular loss over time. This is why you should NEVER should pressure wash, brush, scrape or use high powered air to remove moss instantly.
The only way to follow the instructions from the leading roof manufactures is to apply sodium hypochlorite (AKA bleach) at a rate of 50% bleach and 50% water. Spray this mix to the roof surface thoroughly using a pump sprayer in order for the moss to take the bleach. Adding soap such as Dawn dish soap to the mix will help the bleach and water run slower down the roof surface. This will keep the bleach in contact with the moss for a longer period. Leave the bleach on the surface for 20 minutes or more. Followed by a rinse off using garden hose water. Repeat as needed until all the moss is no longer green. Depending on the type of moss present, you can normally expect the moss to turn white immediately. The moss is now 100% dead and will start dissolving over time. Mother nature will do the hard work for you. The dead moss will dissolve over time and after 60 days or so you will notice a clean roof. You can spray the bleach and water with a simple 1 gallon or 2 gallon pump sprayer from your local hardware store. Keep in mind that it takes years and years for moss to grow. If you have a lot of moss build up I recommend repeating this process 2-3 times.
Living in the Seattle area where moss is our state plant (I know moss is not a plant and a fungus) I have learned a lot. I keep on seeing homeowners and contractors using pressure washers or stiff bristled brushes to remove moss from roofs. Sure the roof looks nice and clean from the ground. However, the damage up close is devastating. These roofs will suffer from rapid granular loss and the expected life time of the roof system will be cut short. Another huge disadvantage is all the alive moss that is blown or swept off the roof is now on all the ground surfaces. The moss will now spread in the lawn, landscaping, walkways, driveways, and everything else near the roof edge. Using a brush or pressure washing the moss will remove the moss but not the spores. This makes the moss return rapidly. This is why its best to kill the moss using bleach and water. It really makes sense once you know your options.
I have used the water and bleach method on thousands of roofs covered with moss and typically we see 5 years before new moss comes back. There are several companies that call the water and bleach solution “soft washing”. If you are looking for a professional roof cleaner or you want to do the process yourself just make sure to use the soft wash method for the best results possible with ZERO damage!
*This method will work on Cement tile roofs as well. We do not recommend this process on Cedar shake roofs or metal roofs. Please take look at this YouTube video of a house with heavy moss in Seattle area. Also please check out the link to the Asphalt Roofing Manufactures Association below: