How to clean a roof

Brett Dvoretz

Avoid corrosive chemicals and chlorine bleach when cleaning your roof. While they might kill algae and moss, they can also damage the roof and nearby landscape.

What is the best way to clean a roof?

Have you noticed your roof looking a little worse for wear lately? Does it appear dark or discolored in some areas? If so, it is probably time to clean it.

Cleaning your roof may sound like an intimidating job, especially if you have never done it before. But this handy guide will provide a breakdown of the process, materials you’ll need and the best method to clean your roof effectively.

What causes roof stains?

Roof stains are a common problem for homeowners. Various types of algae and moss typically cause these stains, but the most common culprit is Gloeocapsa magma. Gloeocapsa magma is a type of algae that grows on your roof and tends to look like black stains or streaks. The second most common cause is a type of moss called Ceratodon purpureus, or fire moss. Fire moss looks like green vegetative growth sprouting out of the rooftop.

What happens if you don’t clean your roof?

If you do not clean your roof, excess algae and moss can cause leaks or shorten the roof’s lifespan. Algae buildup can affect the integrity of your shingles by degrading the limestone. If too much moss grows under shingles, it can push them out of place, resulting in open spaces for debris to collect. All these things can seriously compromise the effectiveness of your roof and the safety of your home.

Tips for cleaning your roof

Before you clean your roof, make sure to check the weather. Most chemicals require several hours of dry weather to soak into the roof. Ideally, it’s best to clean your roof when you have at least 12 hours of dry weather following treatment.

Also, be sure to buy a roof treatment intended for your roof type. Different roofing materials require different treatments. Take time to read the directions carefully before getting started, especially since each cleaning agent requires specific instructions.

What equipment do I need to clean my roof?

Cleaning a roof can be easy if you have the right tools for the job. Before getting started, make sure you have the following items:

A step-by-step guide to clean your roof

  1. Start by protecting the landscaping around your home. Take a moment to ensure any roof runoff directs away from your plants and check your gutters for leaks or blockages. It’s also a good idea to spray landscaping with water before you get started. This will lessen the chance of plants absorbing harsh chemicals from your roof.
  2. Mix your roof cleaning treatment in a garden sprayer according to the manufacturer’s guidelines. Be sure to note how concentrated your mix should be, how long absorption takes and any other important details about application.
  3. Fasten your harness’s rope to your roof using a roof anchor. Do not secure the rope to gutters or anything that cannot support your body weight. Then put on your harness, position your ladder securely against the roof and slowly climb up.
  4. Start applying your cleaning solution at the highest point of the roof and work your way down. The goal is to cover the roof without over-saturating it. Allow the treatment to soak in, and if you notice areas with heavy staining, reapply a little more treatment to those sections.
  5. If you have a metal roof, you can lightly scrub away excess moss or algae accumulation with a stiff scrubbing brush. Note that you should not scrub shingle roofs since scrubbing can damage the shingles.
  6. Depending on the cleaning solution you choose, you may need to wash the treatment off with water. Follow the manufacturer’s guidelines so you do not over-saturate your roof with chemicals.
  7. When you’ve finished spraying your roof, climb down and take time to hose off the landscaping close to your house. Spraying down plants will remove any chemicals that may have landed on them. Remember, some roof cleaners do not need a wash-off, so it’s best to avoid spraying the roof during this step.
  8. Depending on the cleaning solution and application, you should start to see results within a day or two. Results should improve over the following months with subsequent rainfalls.

Should I use a pressure washer on my roof?

Many people consider using a pressure washer to remove algae and moss instead of harsh chemicals. While pressure washers effectively clean sidewalks, pavers, and other surfaces, they will likely damage shingles and affect the overall integrity of your roof. We don’t recommend using a pressure washer to keep your roof clean.

How to prevent roof stains

It’s always a good idea to combat algae and moss with proactive, preventative measures. Here are a few ways to prevent roof stains on your home.

If you have a shingle roof, install small strips of copper sheet metal or zinc-coated sheet metal just below the ridge of each shingle. When it rains, the copper or zinc will run down your roof and kill the algae before it starts to grow.

It’s also a good idea to cut back any tree limbs that touch your roof or block direct sunlight. Tree trimming prevents debris accumulation and allows rainwater to dry more quickly. Since algae and moss grow in damp places, this is a simple and effective way to hinder growth.

You can also use a leaf blower to clear your gutters of leaves and debris. Clear gutters allow for proper water flow and discourage algae growth.

Brett Dvoretz is a writer for BestReviews. BestReviews is a product review company with a singular mission: to help simplify your purchasing decisions and save you time and money.

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