Homeowners in humid areas are no strangers to those unsightly dark streaks on asphalt shingle roofs. While they may look like dirt, mold, or defective shingles, it’s a blue-green algae called Gloeocapsa Magma that causes the stains. Airborne spores spread the organism, and while it doesn’t significantly damage your roofing, it doesn’t do you any favors regarding curb appeal.
If you’re tired of seeing the streaks on your asphalt shingle roof, several effective methods exist to remove and prevent black algae stains.
Algae Resistant Shingles
Have you ever noticed how these algae stains rarely appear directly beneath metal flashing around chimneys or vents? That’s because galvanized sheet metal’s copper and zinc coating is toxic to algae. When it rains, the water washes trace amounts of the metal down your roof and inhibits algae growth in those areas.
If you haven’t noticed this, roofing manufacturers did. Recently, they’ve begun incorporating copper granules into roofing products to create algae-resistant shingles. These innovative shingles provide a long-term defense against unsightly algae stains.
For homeowners who live in areas where algae growth is common, ask about algae-resistant shingles when it’s time to replace your roof. Consult with local roofing professionals to determine if these shingles suit your specific climate and roofing needs. Roofing contractors can also provide insight into the best brands and types available.
These shingles maintain the roof’s appearance and extend its lifespan by reducing the need for frequent cleaning. However, you’ll want to weigh the initial costs against the long-term benefits when considering algae-resistant shingles.
While these shingles may cost more than traditional shingles, they can save money in the long run by lowering maintenance costs and preserving your roof’s appeal. Additionally, these shingles can increase or preserve a home’s resale value by maintaining curb appeal.
Read also: What to Know About Composite Roof Shingles
Chemical Cleaning
What if you have existing algae stains? Chemical cleaning is an effective removal method, but it’s only a temporary fix. Stains often return over time if you don’t take preventive measures. Think twice about the repeated use of harsh chemicals or pressure washing, as these can potentially damage asphalt shingles or shorten their lifespan.
Manufacturers have released several products specifically designed to remove algae stains from roofs, such as Wet & Forget Outdoor. Alternatively, a homemade mixture of trisodium phosphate (TSP), bleach, and water can also effectively remove black roof stains. For those concerned about the environmental impact of their cleaning products, oxygen bleach is a less harmful option, though it may not produce as immediate or dramatic results as chlorine bleach.
To safely clean a roof using bleach, you’ll need items such as a cleaner (store-bought or homemade), a pump sprayer, a garden hose with a spray nozzle, safety glasses or goggles, rubber gloves, a safety rope, old clothes, slip-resistant shoes, and a ladder.
The basic formula for a homemade cleaning solution is:
- 1 quart bleach (6% sodium hypochlorite)
- 1-gallon water
- 1/4 cup TSP (trisodium phosphate) or other heavy-duty cleaner
Avoid using cleaners containing ammonia or those not recommended for mixing with bleach, as this can result in dangerous chlorine gas.
Safety
Safety should always be the top priority when climbing out on a roof. Working on roofs can be hazardous, especially when they’re wet from cleaning solutions. Always wear slip-resistant shoes, and use a safety rope. Avoid working a very steep roof, but keep the rope on, regardless.
Don’t forget to protect your skin and eyes when working with harsh chemicals. Wearing safety goggles and rubber gloves is a must. Additionally, since the cleaning solutions can damage your clothes, put on some of your oldest clothes.
In addition to killing algae, bleach can harm or kill plants in your landscape. Before and after applying bleach, wet down any grass, shrubs, or other plants where runoff might occur. For extra protection, cover bushes with plastic after wetting them down.
It’s never a good idea to work alone on a roof. A second person can hold a ladder steady, watch for safety hazards, and call for help if anything goes wrong. Additionally, check the weather report before heading outside. Windy, rainy, or excessively hot conditions can increase the risk of accidents.
Cleaning
For optimal results, pick a cloudy day to clean the roof. On hotter, sunnier days, the cleaner will evaporate too quickly. If you know who manufactured the shingles on your roof, contact them or check their website for specific cleaning recommendations.
Mix the cleaning solution in a pump-type garden sprayer to clean the roof, following any manufacturer’s instructions. Then, carefully move onto the roof and wet it with the solution. Tackle the roof in sections to ensure thorough application. After applying the solution, let it sit on the roof for about 15 minutes to effectively break down and remove the algae stains.
Once the solution has sat on the roof for the required time, rinse thoroughly with a hose. Go slowly and deliberately while rinsing to remove all of the cleaning solution and dislodged algae.
Always follow the manufacturer’s instructions for the best and safest results when using a commercial roof cleaning product or oxygen bleach. Proper use can vary regarding application technique, setting time, and rinsing recommendations. Following these instructions also helps minimize any potential damage to the shingles.
Preventing the Return of Algae
After successfully cleaning the roof, you’ll want to take steps to prevent algae from returning. Installing metal strips can prove an effective long-term solution because they work with rainwater to distribute metal ions across the roof’s surface. Every time it rains, you’ll be fighting algae growth.
Consider installing a strip of copper or zinc-coated sheet metal along each side of the roof, just below the ridge. To be effective, two to four inches of metal should be visible on the roof.
To install metal strips, start by securing narrow strips directly to the roof using roofing nails or screws with rubber washers. For wider pieces, loosen the self-sealing tabs on the top row of shingles with a putty knife. Carefully slip part of the sheet metal under the loosened shingles, ensuring it sits flush with the roof so it doesn’t catch rainwater or debris. Finally, use roofing nails to nail the metal in place under the shingles.
A more budget-friendly option, galvanized sheet metal is less toxic to algae but still effective. Both materials are available in rolls of various widths and thicknesses from local metal suppliers and online retailers. Alternatively, homeowners can purchase zinc strips specifically designed to eliminate roof algae from specialized suppliers.
These prevention methods can also be effective against moss growth, as moss thrives in similar humid, shady conditions.
Professional Cleaning Services
While removing algae as a do-it-yourself project is possible, you may prefer to hire a professional roof cleaning service. These experts have the equipment and experience to safely and effectively remove algae stains without damaging the roof.
Professional cleaners often use specialized low-pressure washing techniques and eco-friendly cleaning solutions that are less likely to harm shingles or your bushes and plants. They can also inspect the roof for damage or potential issues while cleaning.
When considering professional services, research local companies and read customer reviews to find out if other homeowners have had positive experiences and found them reliable. Check that anyone you hire has the proper license and insurance. Liability insurance protects you from paying a homeowners claim if someone gets hurt on your roof.
Take the time to ask them about their cleaning methods and products, focusing on eco-friendly and effective solutions. And, anytime you hire someone to work on your home, request a detailed estimate before committing to the service to avoid hidden fees or unexpected costs.
While professional cleaning may be more expensive than doing it yourself, it can save time and potentially prevent costly mistakes and accidents.
Maintaining a Clean Roof
Regular roof maintenance can help prevent algae growth and extend the time between when you need to clean.
Trim any overhanging tree branches to increase sunlight exposure and reduce moisture retention. This keeps algae from growing and prevents debris from accumulating and potential damage from falling branches. Remove any debris, such as leaves or small branches. They can retain moisture and provide nutrients for algae.
Clean gutters regularly for proper water drainage. Blocked gutters can lead to water pooling on the roof, which fosters an ideal environment for algae to grow. Conduct annual roof inspections to catch any issues early. These inspections can identify problems like missing shingles, leaks, or early algae or moss growth signs.
When you incorporate these maintenance practices into your home care routine, your roof will stay clean for longer. A proactive approach to roof maintenance contributes to your roof’s long-term health and durability.
Final Thoughts About Removing and Preventing Black Algae Stains on Asphalt Shingle Roofs
While the ugly black stains on your roof may seem daunting, there are effective methods for both removal and prevention. From chemical cleaning to installing algae-resistant shingles or metal strips, homeowners have several options to combat and remove algae.
The key is to address algae growth promptly and take preventive measures to maintain a clean, attractive roof. When you do so, you’re preserving your roof’s appearance, potentially extending its lifespan, and keeping your home’s curb appeal for years to come.
Further Information
- How to Remove Moss from a Roof (article)
