How to Clean Roof Shingles

Preparing Your Roof

Choose a cool and overcast day. The day you perform a deep cleaning on the shingles should be cool and overcast. Sunlight and warm weather will ensure the cleaning solution dries too fast to be of any use. In addition, choose a day with little wind so that when you spray the solution, it stays on your roof.

Perform maintenance on your roof. Before you begin, it’s important to repair loose shingles and flashings to minimize roof damage. Afterward, clean out your gutters and downspouts. You’ll need the cleaning solution to drain off the roof during rinsing.

Protect your yard. Move any furniture away from the work area. If you’re using a bleach solution, also cover your yard. Rinse down your lawn and plants before you begin deep cleaning so the water dilutes harmful bleach, then cover them with plastic to catch any spray.

Remove debris from the roof. Before you clean stains, you’ll have to climb up onto the roof and take off twigs, leaves, and anything else that would get in the way. Pick them up with your hand, use a leaf blower, or gently sweep them off with a broom.

Cleaning Your Roof

Mix your cleaning solution. A home cleaner can be made with a quart (.95 L) of standard laundry bleach and a gallon (3.8 L) of water. Optionally, add ¼ cup (177.5 mL) of a non-ammonia heavy cleaner such as TSP (trisodium phosphate) for extra cleaning power. Bleach is caustic to the roof and plants. At most, the bleach should be 50% of the solution. Lye products also work but are caustic to the skin and should only be handled while wearing protective gear. If you'd rather buy a cleaner from the store, look for a detergent specifically made for shingled roofs.

Soak the shingles with water. Bring your garden hose or water sprayer up to the roof. Starting from the bottom, carefully wet the shingles. This keeps the solution from drying out immediately after application. When you see runoff, stop.

Spray your cleaning solution. Load the solution into a sprayer. Using slow, even strokes, coat the shingles. Make sure you don’t miss any spots, or else your roof will come out spotted. Leave the solution to soak in for 15-20 minutes.

Rinse off the solution. Use a water sprayer to apply enough force to dislodge algae and moss without damaging the shingles. In the case of a lightly-stained roof, a garden hose may also be enough. Again, move slowly. Move back and forth in even strokes, making sure you reach all of the cleaners. Power washers should never be used. They will wear away your shingles.

Reapply the solution. For deep stains, you’ll have to put on more solutions. Let the roof dry first, then wet the roof and spray on more the same way you did before. Wait no more than 30 minutes and rinse it off again. Light stains left at this point may wash off over time as long as rain and sunlight can reach the area. A broom can also be used to scrub in cleaner. Use a broom with medium-stiff bristles and apply little pressure so you don’t damage the integrity of the shingles.

Maintaining Your Roof

Clean your roof regularly. The debris, including fallen branches and leaves, provides a moist environment for moss and algae. It should be picked up, swept off, or blown off regularly to avoid facilitating growth. Tackle the gutters too so that water drains freely. Prevention makes stain cleaning much easier later on.

Trim nearby branches. Overhanging plant life creates the cool, shady environment that moss and algae need to bloom. Trim tree branches and other plants casting shade on your roof or consider moving them. Exposure to sunlight will keep many moss and algae spores from activating.

Apply a stain blocker. Specialized stain blockers offer resistance for up to three years. Search for roofing algae and moss blockers at a home improvement store. After you clean your roof, spread the stain blocker according to the directions on the label.

Place metal strips under shingles. Copper and zinc strips, found at home improvement stores, can be placed under shingles. When it rains, the water washes away some of the metal, which destroys moss and algae spores. Installing these strips can puncture sealant on the shingles, so it’s best to do this when placing a new roof. Stringing copper wire may work instead.