Remove moss using a pressure washer only if you know how to regulate the amount of pressure coming from your washer. While moss can quickly damage a rooftop, uncontrolled pressure-washing can do even more damage to the roof. Some experts suggest using pressure washers at any pressure level will only do damage to your roof over the long haul.

Preparing to Wash

Before getting your pressure washer up to roof level, spend some time preparing the roof for cleaning. Comb the entire roof surface to pick up any large, loose debris pieces. Look for worn, loose or missing shingles. Avoid any damaged areas with the washer or you'll end up tearing them completely off the roof and doing more damage. If you decide to pressure-wash the moss off of the roof, use a pressure washer with no more than 2000-psi pressure. Adjust the output pressure, if your machine is capable of psi adjustment, to the lowest psi available to start. If your pressure washer doesn't adjust, use the lowest-output nozzle you have. Attach a 25-degree- to 45-degree-angle nozzle if you have one. Choose a solution to clean the roof with. Water will do the trick, but if you want to use a cleaning chemical, make sure it doesn't stain the surface of your home or roof. Find a chemical that's safe for the environment and won't kill your plants, and always rinse with plenty of water after each application.

Washing the Roof

Start at the lowest pressure possible and work your way up to a pressure that pushes the moss away without removing any of the surfaces on your roof. Test the pressure in a corner of the roof---once you see it's not damaging your shingles, start at the highest point of the roof and work your way down. Avoid lifting shingles by never pointing the pressure washer up the surface. Always keep the nozzle at least 8 inches from the surface and angled at 45 degrees to avoid tearing up the surface. If you use a cleaning solution, it should only sit for 10 to 15 minutes before being thoroughly rinsed off.

Alternatives to Pressure Washing

You can use a garden hose and scrub brush as an alternative to the pressure washing, but the job will be much more time-consuming. According to Popular Mechanics, if you install zinc strips on the roof once it's free from moss, the zinc will prevent future growth.

Source:

AskTheBuilder.com: Roof Cleaning

Sound Home Resource Center: Pressure Washing Your Roof

Popular Mechanics