How to Clean Roof Shingles

Increase the lifespan of your roof by keeping it clean

Cleaning your roof shingles should be a yearly task; think of it as a part of spring cleaning. When the cleaning bucket comes out, the ladder and garden hose should follow. Cleaning an asphalt roof may seem daunting, but it's a relatively simple task that, done with enough care, can increase the lifespan of your roof for years.

We'll explain how to clean roof shingles with a few different methods, including chemical cleaners, mild detergents, and just water. We'll also show you what to look for and what to be wary of as you inspect your roof for its yearly cleaning.

What Causes Black Streaks On Roof Shingles?

The black streaks on roof shingles are caused by a buildup of blue-green algae called Gloeocapsa Magma. This type of algae is attracted to the limestone in shingles and feeds off it. Over time, the growth will cause the streaks you see on your roof.

The streaks are unsightly and can make your whole house look dirty from the street. In addition to being unattractive, the algae growth can shorten the lifespan of your roof by trapping moisture in the shingles and causing them to degrade quicker.

Two Common Types Of Algae On Your Roof

While there are over 20,000 species of algae, only two are commonly found on roofs in the United States.

The first is Gloeocapsa Magma, which we've already mentioned. This is the most common type of algae that causes those black streaks on your roof.

The second type is called Tremella Mesenterica, which is a white alga that commonly appears in patches. While not as damaging as Gloeocapsa Magma, it can still shorten the lifespan of your roof if left untreated.

What Is The Best Way To Clean A Roof

The best way to clean a roof depends on the type of roof shingles you have and the severity of the algae buildup. For example, if your roof is made of slate or tile, you'll want to avoid using any harsh chemicals as they could damage the components that hold the roof together.

If you have an asphalt shingle roof, you have a few more options available to you. For example, you can use a chemical cleaner, a mild detergent, or just water. We'll go over each of these methods in more detail below.

Roof Cleaning With A Pressure Washer

While cleaning your asphalt roof with a pressure washer might seem like a quick way to see results, it's probably going to speed up more than just the cleaning process. Pressure washing asphalt or composite shingles can prematurely age them by causing the granules to come off or lifting shingles and allowing in moisture.

Not only will this make your roof look old, but it will also leave it unprotected from the sun's UV rays, which can cause the asphalt to deteriorate and shorten the lifespan of your roof.

No matter how careful you are, we recommend avoiding pressure washing your roof shingles altogether.

Cleaning Roof Shingles With Bleach (Pool Shock)

One of the most common ways to clean roof shingles is with a chlorine-based cleaner, also known as pool shock. This method is effective at killing algae and will give you visible results quickly.

To use this method, mix 1 lb of pool shock per gallon of water and apply it to your roof with a pump sprayer. Let the mixture sit on your roof for 20-30 minutes before rinsing it off with a garden hose.

You should always take caution when using any chemical cleaning product on your roof. Be sure to read the manufacturer's instructions carefully and always wear gloves, eye protection, and a face mask when handling pool shock. It's also a good idea to test the cleaning solution on a small area before you treat the entire roof surface to help you avoid any unwanted damage or discoloration.

To clean your gutters of algae at the same time, mix 1 cup of pool shock per gallon of water and pour it into your gutters. Let the mixture sit for 15-20 minutes before flushing it out with a hose or garden sprayer.

As the pool shock rinses off your roof, you'll want to be sure you lay down plastic to divert the chemical from your lawn or any other plants you have near your home.

Other bleach-based cleaners you can use include:

Oxygen bleach (Oxyclean)
Chlorine bleach (Clorox)
Peroxide-based bleach (Hydrogen Peroxide)

If you plan to use any of these types of liquid bleach, be sure to dilute the mixture and apply it in tiny portions directly to algae to prevent staining or discoloration.

Algae & Moss Prevention And Cleaning For Asphalt Shingles

Roof algae and moss prevention begin with good roof maintenance and proper ventilation. Inspect your gutters and downspouts to ensure they are clean and free of debris. This will help keep water flowing freely away from your home, rather than giving it a chance to pool on your roof.

It's also important to trim any branches that are hanging over your roof. Removing tree branches will help prevent leaves and other debris from clogging your gutters, giving algae a place to grow.

Proper ventilation is key to preventing algae growth on your roof. Make sure your attic is well-ventilated to allow heat and moisture to escape. Circulating air will help keep your home cooler in the summer and prevent condensation in the winter.

You can also install a roof-mounted exhaust fan to help remove heat and moisture from your attic. Just be sure the fan is vented to the outside of your home, so you're not just moving the air around.

If you already know your roof tends to grow algae, consider the following methods to catch it early.

Inspect your roof regularly for any signs of algae growth. The sooner you catch it, the easier it will be to clean.
After heavy rain, check your gutters and downspouts to make sure they're clear. This will help prevent any standing water from pooling on your roof.
Consider having a professional roofer apply a protective treatment to your roof to help prevent algae growth in the future.

Cleaning An Asphalt Shingle Roof | Step-By-Step

Once you've gathered the materials you need to clean your roof shingles and prevent algae growth, it's time to get to work. Follow these steps to give your asphalt shingle roof a good cleaning:

Trim Overhanging Branches: Begin by trimming any branches hanging over your roof. This will help keep leaves and other debris from clogging your gutters and encouraging algae growth after you finish your project.
Clear Debris: Once you've trimmed the trees, clear any debris from your roof, gutters, and downspouts. This includes leaves, sticks, nests, or other items you can quickly clear off your roof.
Pre-Rinse Roof and Vegetation: If you have a pressure nozzle on your hose, you can use it to gently rinse off any loose dirt or debris from your roof. It's also a good idea to pre-soak any plants that could collect runoff chemicals while cleaning. Just be sure to use a low-pressure setting to avoid damaging your plants and shingles.
Mix Cleaner: After removing the debris, mix your chosen cleaner in a bucket or pump sprayer according to the manufacturer's instructions.
Apply Cleaner: We recommend applying the cleaner to your roof with a pump sprayer, fully saturating areas with algae growth. Let the cleaner sit on your roof for 20-30 minutes before scrubbing to allow it to loosen the dirt.
Treat Stains: Use a sponge, soft brush, or cloth to scrub at set-in stains gently. If you still notice discoloration after treatment, you can double-treat the area with your cleaner.
Rinse Cleaner: Use your garden hose to rinse the cleaner off your roof gently. Be sure to lay down plastic to catch any runoff that may reach the ground to prevent any chemicals from getting into your lawn or garden.
Double Check Gutters: Once you've rinsed off the cleaner, inspect your gutters and downspouts to ensure they're clear. If they're not, you can use a small hand shovel or spade to remove any debris.

Safety

While working on your roof, it's essential to take some safety precautions, including what you wear, how to plan to reach your roof, and the methods you use to clean. Follow our tips below for a safe and worry-free job.

Don't walk on a wet roof: Remember that a wet roof will be slick, and you should avoid walking on it while it's saturated or at all if you can reach it from a ladder. Instead, descend the ladder and move it to where you need to access the roof. Once it's secured, re-climb and resume cleaning. Do not lean away from the ladder, remove one foot from the ladder, or tip the ladder to reach any part of your roof.
Wear proper safety gear: If you plan on working with any chemical roof cleaner, we recommend you wear gloves, long sleeves, and pants to protect your skin from the chemicals. You should also consider wearing safety goggles to guard against splashes and a face covering to ensure you don't inhale toxic fumes.
Practice ladder safety: If you're using a ladder, set it up on level ground and have someone hold it steady for you. If your ladder teeters as you climb it, it's not in a safe position.
Consult a roofer: If you have any questions or concerns, consult a professional roofer. Our team can advise you on the best way to clean your specific type of roof and let you know if your roof is in good enough condition to climb. A roof inspection is an excellent way to learn how to care for your roof properly.

Prevention

The best way to deal with algae on your roof is to prevent it from happening in the first place. Here are some tips for preventing algae growth:

Install Zinc or Copper Strips: You can purchase these strips at your local hardware store. Just attach them to the peak of your roof, and they will release zinc or copper into the rainwater as it flows over them. These metals are toxic to algae and will help prevent them from growing on your roof.
Keep Your Gutters Clean: As we mentioned before, clogged gutters can lead to standing water on your roof, a prime breeding ground for algae. Be sure to clean your gutters regularly to prevent this from happening.
Trim Trees and Shrubs: Overhanging branches can drop leaves and other debris onto your roof, providing food for algae to grow. Trimming back any trees or shrubs near your home will help prevent this.
Apply a Protective Treatment: You can purchase a roof treatment that contains copper or zinc at your local hardware store. These treatments will help prevent algae from growing on your roof and can extend its lifespan.

Cleaning Roofs With Uncommon Shingles

Distinct roofing materials require different cleaning methods. Here are some tips for cleaning roofs with uncommon shingles:

Clay Tiles: Clay tiles can be cleaned with a mixture of water and dish soap. Because they are resistant to most types of stains, they shouldn't require aggressive cleaning. Just be sure to rinse the tiles thoroughly afterward, and your tiles will look as good as new.
Slate Tiles: Slate tiles can also be cleaned with a mixture of water and dish soap. You can also use a soft-bristled brush to scrub away any stubborn dirt or debris, but keep in mind these tiles tend to be fragile despite their weight. Do not vigorously scrub or use harsh chemicals on slate tiles.
Wood Shingles: Wood shingles can be cleaned with a mixture of water and bleach in a 3 to 1 ratio. You can also use a soft-bristled brush to scrub away any stubborn dirt or debris. Remember that wood shingles naturally discolor over time, and while power washing might restore the standard color, it can also damage the wood.
Cedar Shakes: Cedar shakes can be cleaned with water and wood cleaner. You generally don't want to use bleach due to the porous nature of the wood. You can also use a soft-bristled brush to scrub away any stubborn dirt or debris. If you do notice algae stains, you must act quickly. Algae can cause a moisture buildup in the wood, which can prematurely age shingles and lead to leaks.

What Happens If You Don't Clean Your Roof?

If you don't clean your roof regularly, nothing will happen for a while. Roofs are made to withstand a fair amount of wear and tear but left with enough time, they will eventually become covered in algae, moss, lichen, and other debris. These growths can cause your roof to deteriorate due to trapped moisture, lifted and damaged shingles, and wood rot. In extreme cases, after enough time passes, an unclean roof can collapse under the weight of the debris and trapped moisture. Regular cleaning will help extend the lifespan of your roof and prevent costly repairs.

To Eliminate Risk, Hire A Professional

Cleaning your roof can be risky, especially if you're uncomfortable working on a ladder. If you're unsure how to clean your roof properly, it's best to hire a professional roofing company to do it for you. They have the experience and knowledge necessary to safely and effectively clean your roof without damaging it.

A clean roof is a happy roof. By following the tips in this article, you can keep your roof free of algae, moss, mildew, and other debris.