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What is the Best Way to Clean a Roof? (And is it Even Necessary?)

What is the Best Way to Clean a Roof? (And is it Even Necessary?)

Next time you walk around your neighborhood, take a look up. Not to the sky, or the clouds, or maybe a bird or a plane passing overhead. Take a look slightly below that, at the roofs that top the homes around you.

What kind of shingles do they have? Are they all the same color? Do any that you see have any visible cracks or chips in them?

Wait. What’re those black streaks? That does not look good. Does that mean that roof needs to be replaced? Does MY roof have some of that stuff on there? How have I never noticed this before? What on earth can I do to clean that stuff off?

Calm, dear reader. A stroll through your neighborhood should be a peaceful experience, not one that turns to panic because of a little algae.

Yep, that’s right, those black streaks on the roofs around you are algae, the same stuff that grows on water, too!

Before you freak out about that and start pressure washing your roof to get it off, take a moment to read this blog. We’ve been answering questions about algae from Raleigh-area homeowners since 1991, so we’re here to help!

We’re going to cover:

Let’s jump in!

Why Should You Keep Your Roof Clean?

You might be thinking, "Do I really need to clean my roof?" It's not like you’re spending a lot of time up there or anything, right? But trust us, neglecting to clean your roof can cause some serious problems.

more black streaks and spots


One big reason to clean your roof is to prevent the growth of algae, like we mentioned earlier, and moss. These organisms love warm, humid spots and can quickly take over your roof, especially in shaded areas. Not only do they look nasty, but they can also mess up your shingles and roof structure over time.


While algae doesn’t have as much of a direct affect on your roof’s life, moss can trap moisture against your roof, and grow up under shingles ,and causing them to deteriorate faster and possibly create leaks.

Another reason to keep your roof clean is to get rid of debris like leaves, branches, and twigs. If left on your roof, this stuff can pile up and block your gutters and downspouts. This can cause water to overflow and back up, leading to water damage to your roof, siding, and foundation.

Plus, cleaning your roof can boost your home's curb appeal. A sparkling clean roof can make a big difference in how your home looks and even increase its value if you ever decide to sell.

So there you have it, folks. Keeping your roof clean might not be the most fun chore, but it's definitely worth it to protect your investment and make your home look its best!

What is roofing algae?

black streaks

So now to answer one of the questions we posed at the beginning of this article, what is roofing algae?

The algae that we see on our roofs is not actually algae at all, or even a plant! It’s actually Cyanobacteria, also known as blue-green algae, because of how it appears and where it grows.

This stuff usually appears as dark streaks or patches and can make your roof look pretty unsightly. It tends to grow in areas that are shaded or don't get much sunlight, and can spread quickly if left untreated.

The algae does not pose an immediate threat to your roof, but it can cause your shingles to wear more quickly than they otherwise would. Algae can hold moisture against your shingles, which can cause them to deteriorate faster and eventually lead to leaks. Plus, it helps create an environment that encourages the growth of moss and other more damaging plants.

Roofing algae may be a pain to deal with, but it's not the end of the world. With a little elbow grease or the help of a professional, you can get rid of it and keep your roof in tip-top shape!

What is the best way to clean your roof?

Unfortunately, a quick rinse won’t do your roof much good. In fact, it will actually cause it a lot of harm.

Spraying your roof with just water won’t affect the algae at all, and it will cause protective granules to run off your roof. If you were to use a pressure washer, you may get some algae off, but it won’t kill the bunch, and you’ll be blowing off so many granules that you’ll be wearing your shingles down at a really quick rate.

covered plants

The good news is that roofing algae can be removed with a thorough cleaning. You can use a specialized roof cleaner or a mixture of water and bleach to get rid of the algae. However, in our opinion this is not necessarily a job that should be tackled yourself, unless you can reach the affected area by spraying it from the ground. You also should not be getting up on the roof to do something like this, as the water will make the area very slick, and greatly increases your chances of falling off and getting injured.


There are chemicals involved, like bleach, so it should ABSOLUTELY NOT be handled without proper protective equipment like gloves, goggles, and clothing that will protect your skin from the bleach. Also, you’ll want to make sure any plants won’t be sprayed or dripped on in the process, as the chemicals could cause a lot of damage to them as well.

There are several options for professional roof cleaning, as contractors often will add that as part of their services. So, especially if you have a larger or taller roof, it’s a good idea to reach out to them to see how much it would cost you.

How much does roof cleaning cost?

The cost of roof cleaning services can vary depending on a few different factors.

The size of your roof is one of the main factors that will affect the cost. Obviously, a larger roof is going to take more time and effort to clean than a smaller one, so you can expect to pay more for a bigger roof. The slope of your roof can also affect the cost, as steeper roofs are more difficult and dangerous to clean.

nice clean roof

On average, you can expect to pay anywhere from $200 to $800 for a professional roof cleaning service. Again, this will depend on the factors mentioned above as well as the location of your home and the company you choose to work with.

While this might seem like a lot of money, keep in mind that professional roof cleaning can save you money in the long run by prolonging the life of your roof and preventing costly repairs. Plus, it can improve the overall look and value of your home.

So, if you're on the fence about hiring a professional to clean your roof, consider the benefits and shop around to find a reputable company that fits your budget.

If you’re looking to learn more about the algae on your roof, check out our blog on that topic! Or, feel free to read more about the steps you can take to prolong your roof’s life by having a proper maintenance routine!

On Tops Roofing has been helping answer the questions of North Carolina Homeowners since we opened our doors in 1991. Whatever your roofing project requires, we’re on it!

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