How to Clean Asphalt Roofs: Tips and a Quick Process

by Nov 20,2021

Moss and algae are common problems on asphalt shingle roofs. You might have seen this problem before at your own home: Black streaks on the roof or green moss growing on top of the shingles.

The good news is that moss and algae problems on asphalt roofs can be quickly remedied. Yet, it’s important that you properly clean asphalt roof shingles. Asphalt roofs are sturdy and dependable, but using improper cleaning methods can damage or, in the worst cases, destroy your asphalt roof.

For example, pressure washing on asphalt roof isn’t recommended. High-pressure water can penetrate the shingles and damage the roof decking, which could potentially make your roof more susceptible to water leaks. Improper pressure washing techniques can also dislodge shingles.

You might be wondering: What’s the best way to clean an asphalt roof?

Here are some tips and an explanation of why softwashing is the way to go.

Why You Need to Clean Your Roof

You likely want to clean your roof because you’re noticing the asphalt shingles are discolored or there are large patches of what appears to be mold on the roof.

In the overwhelming majority of cases, that’s not caused by mold or mildew, but rather moss and algae. Algae growth is caused when moisture sits on the roof for a long period of time, and that’s why black streaks are common on northern-facing, more-shaded areas. The algae is usually a blackish or green-black hue, and by the time you can see it, that means the algae has been growing for quite a while.

Moss, on the other hand, is a green plant that survives in moist environments. That’s why it’s most common on north-facing rooftops. If left unattended, moss can cause significant damage, curling the shingles, and leaving the roof susceptible to water and wind damage.

Ultimately, regularly cleaning your roof helps prevent algae and moss growth (or remove it, if it’s already present). But there are a few things you need to know to properly remove it to prevent reoccurance.

Roof Cleaning 101: Removing Moss and Algae

To properly remove moss, you need to kill the spores. And the way that you do that is by applying a detergent – usually a mixture of chlorine bleach and water – to the roof. Here are the benefits of applying a detergent:

–   Detergents kill moss and algae.
–   This method ensures the staining won’t quickly return.
–   Detergents more effectively remove moss and algae (compared to pressure washing)

Essentially, you would leave the detergent on the roof for about 15-20 minutes. During this time, it will attack and kill the algae. This makes it much easier to rinse away.

Then, after letting it sit on the roof, the detergent and the algae are removed using a low-pressure softwash. This part is important. You don’t need to apply high-pressure to remove stubborn stains. Instead, if the stain isn’t fully removed after the first rinse, you would reapply and follow the process again.

In the majority of cases, a single application and rinse will clean stubborn roof stains.

Quick Roof Cleaning Tips

Keeping your asphalt roof clean isn’t too difficult of a process. If you’ve recently cleaned your roof, here are some additional steps you can take to prevent moss and algae growth from recurring:

  • Removing leaves/debris – Leaves can carry algae spores, and when they start to pile up in eaves, they can create an environment for algae growth.
  • Gutter cleaning – Clogged gutters from upper roofs will drain water onto lower roofs. The result of this added moisture is often moss or algae growth. Keeping your gutters clear of clogs will prevent this problem.
  • Tree trimming – This is a big one. Trimming trees will not only help you reduce debris and gutter clogs, but it also allows more sunlight to reach the roof, which can prevent algae growth.

Thanks for Reading!

Get your asphalt roof cleaned by professionals. Clean and Clear serves the Twin Cities area, and provides fast and safe asphalt roof softwashing. Schedule an appointment today online.




Exterior property cleaning

We take pride in having top quality cleaning systems and employee training in all areas of our services. Our outstanding customer service and satisfaction has earned the trust of thousands of home and business owners throughout our Minnesota service area since our company began.


We offer services within a 30 mile radius of the Minneapolis and St.Paul metro area. Check all of our service areas/locations.

Call about inquiries outside of these cities.

© 2023 Clean and Clear. All rights reserved.