Some roof cleaning companies recommend that you clean your roof every couple of years, but you might need to do maintenance every year depending on the type of roof you have, the climate and the weather. Roofs in harsher climates tend to require more frequent cleaning.

Yes roofs can be cleaned, and yes, it’s a real thing. Roof cleaning may actually be a wise investment to prolong the life of your roof. Overgrowth of moss, grime, lichen or algae can all shorten the life of your roof. If you have black streaks growing on your roof, they are likely caused by gloeocapsa magma algae spores that have landed on your roof and taken up residence. Once the algae has grown into streaks, the organism has usually been growing for several months and it’s high time to have it removed. If you live in a rainy part of the country, such as the Pacific Northwest, there’s a good chance you’ll find moss growing on your roof at some point. The northern part of your roof, as well as any parts that remain shaded all day, will provide a wet, cool haven for moss to flourish. Unfortunately this water-absorbing moss can damage your shingle roof, leading to rot if not removed. Beyond roof health and function, a clean roof can boost your curb appeal and potentially boost your home’s resale value. The national average for roof cleaning costs ranges between $270 and $350, although prices can be higher depending on how large your roof is, how steep your roof is, and what type of cleaning is necessary. Typically pros use either a pressure wash or chemical wash (made with a concentrated bleach solution) to remove algae, lichen, moss and dirt.

Over time, algae, moss, lichen, dirt and even salt (if you’re near the ocean) can build up on your roof. These buildups can affect the look and function of your roof unless removed. The buildup of organic materials such as moss on a shingle roof can prevent water from sloughing off as it normally would. Trapped water can rot the roof or cause early deterioration of your shingles. Even if you don’t have a shingle roof, moss and lichen absorb water, and that wet material adds weight and stress to your roof — as well as providing a home for insects and other pests, and collecting dirt. For reflective, cool roofs that redirect heat away from the home, algae and moss growths can hamper their ability to deflect the sun, which can affect utility bills. Visually, moss, dirt and algae growths on a roof can have a negative effect on perceived home value and curb appeal. For example, black algae streaks on your roof may cause a potential homebuyer to assume that the roof might need repair or replacement, when it only needs to be cleaned.

There are several reasons why it’s worth it to hire a professional roofer instead of attempting it yourself. The first is safety. Roofing is inherently dangerous, as a fall from a roof could seriously injure or kill you. Roofers have specialized equipment and training to help prevent accidents.  

Next is experience. Roofers know how to spot problems (leaks, missing shingles, moss or mold growth, etc.)  in your roof that could potentially save you from costly repairs down the road. 

And finally, roofers save you time by getting the job done quickly and with a high degree of quality.

Roof cleaning is done to remove moss, lichen, algae, and buildup of other grime and dirt. There are several methods for roof cleaning, which can include a chemical soft wash, pressure washing, low-pressure washing and hand washing. When a chemical soft wash is used, a bleach mixture is sprayed onto the roof. The bleach-based solution is absorbed by the algae or moss, which dies from exposure to the chemical. The roof is then sprayed with a low-pressure rinse of water, which loosens the now-dead material, allowing it to slide off the roof.

For homeowners, the Asphalt Roofing Manufacturers Association recommends a mixture of 50 percent laundry-strength liquid chlorine bleach and 50 percent water. Professional roof cleaning companies will use an industrial mixture that is still safe but may be more effective in eliminating algae and moss growths. Asphalt shingle roofs are the most common type of roof, but each roofing material will have its own cleaning needs, so it’s best to consult with your roofing pro before diving in. Don’t do it yourself unless you can safely navigate your roof, the chemicals and a sprayer system. When in doubt, leave it to the pros.

The national average for roof cleaning costs ranges between $270 and $350. Factors that can affect the cost to clean your roof are the height of your house, the size and pitch (steepness) of your roof, and the complexity of your roof’s design and accessibility. Geographic location also plays a role in roof cleaning costs as regional labor rates and area costs to do business will vary. There are several ways to clean a roof. The most common is pressure washing. Industrial pressure washers can spray over 3,000 pounds per square inch (psi) of water — which is much too powerful for roof cleaning, and may tear off shingles and damage your roof. Confirm that the roof-cleaning pro you choose will only use a low-pressure sprayer to protect your roof investment. For large algae or moss growths, pros often recommend a combination of low-pressure washing with a bleach-based chemical solution. This is referred to soft washing and should handily remove any growths taking over your roof.