How to clean a roof

Cleaning Tools & Supplies

Always follow the manufacturer’s guidelines on the cleaning solution you choose. Some need to be washed off, while others are left on.

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Best way to clean a roof

Are there unsightly black stains on your roof, ruining its curb appeal? Is it giving your home a lackluster appearance? If so, it’s probably time to get up there and clean it. This may seem like a slightly daunting task, but this handy guide shows just how easy it can be.

Keep reading to find out what’s causing those stains, how to get rid of them and what materials you need to ensure the process goes smoothly.

How to clean roof stains

Every homeowner encounters dark stains and other discolorations on their roof at some point. While this can happen for many reasons, there are two main culprits. The first and most prevalent is Gloeocapsa magma. This is a type of algae that produces black, streaky stains. The second most common cause is Ceratodon purpureus, or fire moss. If you see green vegetative growth on your roof, it’s most likely fire moss.

Should I clean my roof?

Not cleaning a roof can have more than just cosmetic repercussions. The buildup of algae or fire moss can damage the integrity of a roof in several ways. If neglected for a long enough period of time, Gloeocapsa magma can degrade the limestone found in most shingles. 

Fire moss doesn’t just grow on top of shingles, but under them as well. As it grows, it can push the shingles up and out of place. Heavy accumulation of both algae and fire moss can potentially lead to leaks over time and significantly shorten the lifespan of your roof.

Roof cleaning equipment

Ask any contractor or mechanic and they can tell you how vital it is to have the right tools for the job. When it comes to cleaning a roof, this is no different. The following equipment can make the task both easier and safer.

Werner Upgear Roofing Safety System

Werner Upgear Roofing Safety System

This OSHA- and ANSI-compliant kit comes with rope, a harness, temporary anchors and everything else you need to secure you safely on the roof. All of its components conveniently store in the included bucket when not in use.

Where to buy: Sold by Home Depot and Amazon

3M Chemical Splash/Impact Goggle

3M Chemical Splash/Impact Goggle

Simple and affordable, these clear polycarbonate goggles can keep your eyes protected from cleaning solution splatter. They’re vented to prevent fogging and are large enough to fit over prescription glasses.

Where to buy: Sold by Amazon

Wet & Forget Roof and Siding Cleaner

Wet & Forget Roof and Siding Cleaner

The Wet & Forget bottle attaches directly to the end of a hose for easy application without any premixing. It can spray up to 30 feet and eliminates many types of mold, mildew, algae and moss.

Where to buy: Sold by Amazon

Hydrotech Expandable Garden Hose

Hydrotech Expandable Garden Hose

At 50 feet in length, this expandable hose from Hydrotech should allow you to reach most places on your roof from a single spigot. A thick latex liner makes it durable, and a heavy-duty brass flow valve allows you to easily start and stop the flow. 

Where to buy: Sold by Home Depot

Louisville Extension Ladder

Louisville Extension Ladder

This ladder comes in several sizes and is crafted from fiberglass, which makes it strong and non-conductive. The 300-pound capacity is more than enough to support most users, and its rubber feet offer a good grip on most surfaces.

Where to buy: Sold by Amazon, Home Depot and Wayfair

The best way to clean a roof

If you’ve never cleaned a roof before, you can follow this simple step-by-step guide to help the process go smoothly.

1. Check your gutters to make sure there are no leaks or blockages. You should also make sure that all runoff from the roof is directed away from plants. 

2. Prepare any landscaping near the house by heavily saturating it with water. This helps reduce the chances of it absorbing any cleaning solution it’s splattered with.

3. Place the ladder securely against the roof and check to make sure its feet are stable. Next, attach your hose to the cleaning solution bottle. If using a different cleaning agent, you may need to premix it in a garden sprayer.

4. Don the harness, climb up to the roof and immediately anchor it in place.

5. Start by applying the cleaning solution at the apex of the roof and work your way down. Follow the manufacturer’s guidelines regarding how much to apply, but most recommend evenly spraying it across the entire roof without oversaturating it. You can apply extra solution in areas of heavy staining.

6. Let the solution soak in for the recommended amount of time and if required, wash it off. If you use a no-rinse cleaning agent, you can skip this step.

7. You can now unfasten your harness anchors and carefully climb down the ladder. Once on the ground, spray down your landscaping again to wash off any chemicals that may have landed on the plants. If you used a cleaning solution that doesn’t need to be washed, do your best to avoid spraying the roof.

8. You should start seeing the effects of your work within a couple of days. The results should continue to improve over the following months.

Roof cleaning tips

Always check the weather before getting started. Most cleaning solutions require at least a few hours to soak in. Only apply them when you expect to have at least 12 hours of dry weather afterward. 

Use a leaf blower to clear debris off the roof before getting started. This ensures nothing blocks the application of your cleaning solution.

If you have a shingle roof, ideally you should avoid scrubbing. However, if you’re dealing with stubborn stains or moss that aren’t coming off with the use of the cleaning solution alone, you can use a deck brush. Be careful not to use too much pressure and always scrub in a downward motion following the lay of shingles. If you scrub too hard, you can damage shingles or move them out of place.

Though you may be tempted to forego cleaning solutions and reach for a pressure washer, this should be avoided. Pressure washers are too powerful and will often damage shingles.

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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