What You Need To Know About Cleaning A Roof

Do you have algae, lichen, or moss on your roof or siding? Not only is it an ugly eyesore, but it can potentially damage and reduce the life of your roof.  Roof maintenance and repair is an important part of home maintenance, but is often overlooked until big problems develop. If you regularly clean your roof yourself, you can keep it looking new and avoid major expenses overtime.

There are two ways to clean your roof, and the type of roofing material you have will determine which method will clean your roof most effectively.

Pressure washing

Use the pressure washing method if you have metal or tile roof.

Chemical washing

Any type of roofing material can be cleaned with chemicals. The most common chemicals used for cleaning the roof are sodium hydroxide, or a chlorine solution.

Pressure Washing

Attach a 35 degree spray nozzle to the pressure-washer hose and fill the pressure washer with a cleaning solution.

Place your ladder where it allows you to get onto the roof without damaging the edge.

Position yourself at the highest point of the roof on the side farthest away from the ladder, and face down the pitch. Make sure to be very careful not to stand on wet roof areas because algae becomes very slippery when wet.

Start at the top of your roof and work your way down. Avoid blasting water up between the tiles or sheets of roofing material because if water gets under the materials it is likely to get into the roof decking and cause even more fungal growth.

Wash the roof in sections, from top to bottom in a steady sweep from side to side. Work your way back to the ladder so you can exit the roof when you are finished.

Chemical Cleaning

Mix the chemical product you chose with water for a 1:7 dilution ratio. Pour it into a pump sprayer, strap yourself in a full-body harness, tie it down and climb to the roof.

Before applying the cleaner, spray the roof with water to cool it down. This prevents the cleaner from drying out too quickly

Saturate a large area of the roof with the cleaner. Start at the bottom row and work up to the top. Spray until you see runoff. If any areas dry, then respray them. Wait about 20 minutes then rinse.

If the staining is fairly light, you can rinse the cleaning solution off with a garden hose. But go slowly and use even strokes.


When cleaning your roof never do it alone, especially since moss and and algae can be very slippery when wet. Always wear a good pair of well fitting, non-slip shoes or boots. It’s always a good idea to wear safety glasses to prevent any chemicals, water, or debris from getting into your eyes. And never forget to wear sun protection.