You mow the lawn, you trim the shrubs, you wash down your driveway and you tend the flowerbeds. You want your house to look great. You want curbside appeal! But, oh, those asphalt roof tiles – how they let you down. Those black streaks, that build-up of mould and lichen. A few years ago they looked great, but now they’re sporting a miniature rainforest of gunge.

Don’t panic! There’s a way you can clean those roof shingles and return them to their former glory.

The Dirt

The dirt coating your roof tiles is made up of airborne pollutants, tree sap, moss, mildew, lichen, algae and mould – quite a combination! Mould, moss and mildew thrive in moist shady areas. Feeding on overnight dew, they generally begin their infestation in the cool shadows of the eves before working their way ever higher up your roof.

The Danger

Besides looking terrible, the organic growth on your roof can shorten it’s life. Algae feeds on the limestone filler that’s used in roof shingles, compromising their surface integrity and reducing their ability to reflect heat. In extreme cases, mould and lichen can work their way under the edges of your asphalt tiles and cause them to lift, making them prone to damage from wind and rain.


Anything that raises levels of light and dryness will have a retardant effect on the organic growth attacking your roof. Removing overhanging tree branches, for instance, will improve air circulation and exposure to sunlight.

A chemical approach can also be used in the war against roof dirt. Placing copper or zinc strips under a row of shingles near the ridge of the roof will prevent mould and mildew. When rainwater comes in contact with these metals and washes over the tiles it produces a chemical reaction that inhibits organic growth.

Cleaning Your Roof Shingles

To clean roof tiles that are already suffering from unsightly discoloration and organic growth follow the steps below.

Cleaning Solution

In a large bucket prepare a cleaning solution by combining:

  • 4 ½ litres of hot water
  • 1 cup household chlorine bleach
  • 1 cup laundry detergent
  • ¼ cup of Trisodium Phosphate


Wet down all surrounding foliage with the garden hose. The water will help protect your lawn and plants from damage due to contact with the bleach solution. Tip: tying heavy-duty garden refuse bags around the outlets of downpipes will prevent bleach runoff entering your garden.

Ensure you have a safe working environment. Use a strong and stable ladder to climb onto the roof and always have someone holding this ladder when you’re on it. Work on a cool day when the wind is not high and there is no likelihood of rain or electrical storms. On steep or very high roofs consider using a fall-prevention safety harness.

Wear appropriate clothing:

  • Non-slip shoes.
  • Protective gloves.
  • Safety glasses or goggles.

The Method

Using a pump-type garden sprayer, coat the roof tiles with the cleaning solution. Work on one section at a time.

Caution: roof tiles are very slippery when wet. By standing near the lower edge of the roof, facing down-slope, and working on a section below you, then moving backwards up the roof with each successive section you’ll avoid standing on wet tiles.

Allow the solution to sit on the tiles for 10 – 15 minutes (no longer) then rinse off thoroughly.

For very badly affected roof shingles you can scrub lightly with a soft broom or sponge mop while the solution is in contact with the tiles. Be careful, though. Roof tiles are granular in their construction and heavy scrubbing can damage their surface. Using a water-blaster for asphalt roof tile cleaning is not recommended for the same reason.

Ensure you rinse gutters and downpipes to prevent corrosion by the cleaning solution.

Allow your roof to dry completely and inspect the results. Chronic mould infestation my require a second cleaning session.

Curbside Appeal

By using a few simple household ingredients, taking adequate precautions for your personal safety, and spending an hour or two perched on your roof you’ll be able to clean your asphalt roof tiles and boost your home’s curbside appeal.

Learn more about cleaning asphalt roof tiles in this video.

How to Clean Asphalt Roof Tiles, 4.5 out of 5 based on 2 ratings

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