After pulling into the driveway last night and noticing dark streaks creeping down the shingles of your roof, you can’t help but wonder what in the world is going on up there? Although dark streaks and green patches aren’t an uncommon sight on other homes in Traverse City, you’ve never noticed them on your own.
Fear not. Roof discoloration is common, especially on asphalt roofs that are exposed to moisture, shade, and organic debris, which is pretty much every home in Northern Michigan. Many times, what some homeowners mistake for dirt or soot is actually a living growth. So, when you see color staining on your roof, the more appropriate question is: What’s really growing up there?
Fortunately, noticing staining on your roof doesn’t always mean it’s time for a new roof, but it may be time for a cleaning. In this article, you will discover what those stains really mean, what can be safely done about it, and when help from professional roofing contractors is warranted. By identifying problems, understanding our local risk factors, implementing the proper cleaning practices, and seeking help when needed, homeowners with asphalt roofs will have everything they need to tackle those mysterious stains once and for all.
Roof Stain Decoder: What’s Really Growing Up There?
Before grabbing the power washer and getting carried away, homeowners must understand what they are actually dealing with because not every dark stain is the same. Algae, moss, mold, and mildew are too often grouped as one issue, but they are not the same thing. The first step in properly cleaning an asphalt roof is to identify the growth and then execute the appropriate response. Use the following stain decoder to determine what is causing the stains on your roof:
Black or Dark Brown Streaking: Most often, black or dark brown vertical streaks running down the asphalt shingles are caused by algae. The fancy name, Gloeocapsa magma, is a blue-green algae that thrives in moist environments. Especially noticeable on lighter colored shingles, the dark streaks can quickly become an eyesore. In early stages, this algae growth is merely a cosmetic concern, but left alone, it can accelerate the deterioration of the roof.
Green, Fuzzy Patches: Moss is usually much easier for homeowners to identify, as it grows in thick, green patches that stand out no matter the shingle color. Preferring shaded, persistently damp areas, moss can form thick mats that trap moisture against the shingles.
Slimy Dark Spots: Mold and mildew usually appear as dark, slimy spots where moisture is trapped on the roof for long periods.
Multi-Colored, Crusty Patches: Often a combination of lichen, algae, and fungus, these crusty discolored spots firmly attach to asphalt shingles and can be harder to remove, increasing the risk of damage to the roof during cleaning.
Not every stain is the result of organic growth; it could be dirt, pollen, or tree sap mimicking biological growth. For this reason, identifying the cause of the roof stain is the best first step in finding a solution.
Next, let’s turn to why roof algae, mold, and moss plague the roofs of homes in Northern Michigan and similar climates.
Why Northern Michigan Roofs Are So Vulnerable
Although neglect can certainly contribute to algae, moss, and related growth on roofs, that is not always the case. In fact, in Traverse City and the surrounding region, the climate creates the perfect conditions for organic growth. With abundant trees, frequent rains, and lake-effect moisture that keeps humidity levels elevated, roof algae and moss can thrive. In areas that are in constant shade on a north-facing roof slope, moisture lingers, giving moss and algae an easier environment in which to grow. With time, spores get airborne and settle in the limestone-rich surface of asphalt shingles and begin to colonize. With the ideal conditions for roof growth, roof staining can be simply a result of the environment. While having a spotless roof is not always realistic, it is important to recognize when what’s growing is cosmetic and when it is a real concern.
When Roof Stains Become Damaging
Most of the time, when moss or algae first appears, it’s strictly a cosmetic issue. As time passes and roof stains are left unaddressed, the organic growth can become problematic. The following are potential concerns for homeowners when biological growth takes off overhead:
Curb Appeal: Although not all biological growth will end in structural damage to the roof, staining can greatly reduce the curb appeal of any home, making it look older and poorly maintained.
Premature Deterioration: Biological growth on asphalt roofs contributes to the premature aging of roofing materials by keeping them persistently damp.
Shingle Displacement: As moss and algae grow, they can work beneath shingle edges and cause them to lift.
Hidden Issues: When organic growth covers large areas of the roof, underlying damage like cracked or missing shingles remains hidden and unaddressed, where it can cause further damage and deterioration.
Addressing organic growth on the roof early is a simple way to avoid early deterioration of shingle roofs and helps homeowners avoid costly repairs. So, how exactly should you go about cleaning an asphalt roof?
The Dos of Cleaning an Asphalt Roof
The best time to take action against a roof growing moss or algae is as soon as it is noticed. If the growth is just beginning and small, merely a cosmetic issue, cleaning is usually an appropriate way to improve the appearance of the roof and avoid further damage from the growth. Safe cleaning practices focus on removing harmful organisms without damaging the shingles. Use the following guidelines to clean your shingle roof safely:
- Do follow all manufacturer recommendations. Different shingles have specific ways to clean them. Before applying any cleaners, always check the manufacturer instructions first. If you are unsure, check with the roofing contractors who installed the roof before moving forward.
- Do use safe cleaning solutions (50/50 diluted bleach solution or a commercial roof cleaner formulated for your specific roof). Apply the solution with soft water pressure.
- Do protect surrounding landscaping by pre-wetting nearby plants and covering more vulnerable plants to keep them protected from cleaning solutions.
- Do plan your cleaning day around the weather. Mild, calm weather is preferred for roof cleaning, while extreme temperatures can make it difficult.
- Do prioritize safety. Wet surfaces are slippery and extreme caution should be used. Anyone cleaning the roof needs to use the appropriate safety gear (non-slip shoes, gloves, sturdy ladder, working partner), and if it becomes clear the job is too dangerous for the homeowners, knowing when to call a professional is essential.
The Don’ts of Roof Cleaning
One of the fastest ways to ruin a roof is by trying to clean it the wrong way. Certain cleaning methods can actually cause more harm than good. Avoid the following:
- Don’t ever use a pressure washer to clean an asphalt shingle roof. High-pressure will remove the granules from the shingles, damaging the surface and compromising the roof’s protective layer.
- Don’t use abrasive brushes or scraping tools that can damage the surface of the shingles. The goal is to remove the organic growth, not the roof underneath it.
- Don’t use unapproved chemicals or mix household cleaning solutions. Mixing solutions is dangerous and can lead to a chemical reaction that produces dangerous fumes if inhaled. Using harsh chemicals can also degrade the roof and harm surrounding plants.
- Don’t walk on moss- or algae-covered roofs, as it is extremely slippery, and avoid walking on the roof whenever possible.
- Don’t assume that every dark stain is algae. It could be from damaged shingles, flashing problems, moisture intrusion, or another roofing concern. When homeowners are unsure, talk with roofing contractors first and get an accurate assessment of what you are looking at.
- Don’t ignore it. Waiting to address heavy growth only makes removal more difficult and increases the chances of additional damage.
Keep Roof Growth From Coming Back
Once the roof is clean, preventing future growth by addressing conditions that stimulate growth can greatly reduce the amount of maintenance homeowners find themselves doing (or hiring out). The following tips can help homeowners reduce the chances of having recurring algae and moss growth on their roofs, or at least slow its growth:
- Trim branches that overhang the roof and keep it heavily shaded.
- Stay diligent about keeping gutters and downspouts clean. This helps prevent backups that cause water to linger at the roof’s edge.
- Inspect your roof periodically, looking for organic growth.
- Consider working with roofing contractors to place zinc or copper strips near the roof’s ridgeline. Rainwater will then carry these metallic ions down the sloping face of the roof, creating an environment less ideal for algae and moss to grow.
- Do not allow organic debris, such as leaves, twigs, or pine needles, to accumulate on the roof that trap moisture.
- Ensure proper attic ventilation so the roof decking can dry more effectively from below.
- When installing a roof, work with Traverse City roofing contractors who install algae-resistant shingles that incorporate copper granules to prevent organic growth, commonly seen on homes in Northern Michigan.
While prevention can slow the growth of algae and moss on roofs, it is not 100% effective. Climate, landscape, and maintenance all play a role in keeping roofs clean from organic debris.
When Cleaning Isn’t Enough, and It’s Time to Call a Professional
DIY cleaning is helpful for the homeowner who takes good care of their home, maintaining the roof, the landscape, and making sure gutters and downspouts are regularly cleaned. Although DIY cleaning works well for light algae on easily accessible roofs, it isn’t always the best solution. The following are signs that a simple cleaning is not the best solution for the roof:
- Heavy organic growth.
- Algae growth mixed with moss or lichen.
- Shingles are in poor condition, such as cracks, curling, missing granules, or missing shingles.
- The underlayment is exposed, and the deck is soft or deteriorating.
- When the roof is steep, the home is multi-level, or the homeowner is uncomfortable working at heights.
- Previous cleaning attempts were unsuccessful or did not last long.
In these situations, cleaning might improve the appearance, but it does nothing to address underlying problems like damaged shingles, roof decking, or persistent biological growth. Experienced Traverse City roofing contractors can safely wash the surface, assess the roof for any existing damage, and recommend repairs or prevention tips tailored specifically for each home. Professional roofing contractors will also help homeowners determine if cleaning is worthwhile or whether the roof needs a replacement.
The Goal is Not Just a Clean Roof, It’s a Healthy One
Not what you wanted to see on your own roof, but black streaks and green patches are not an unfamiliar sight on roofs in Northern Michigan. And while they can certainly be unsightly, they are not always an automatic sign that something is wrong with the roof. Algae, moss, and mildew all behave differently, and identifying what is actually growing on the roof is the first step in finding a solution.
With gentle cleaning, the right solution for the particular shingle, and eliminating shady spots on the roof, homeowners can keep their roofs not only looking better, but performing longer too. When the job is bigger than a homeowner can handle safely, trust a professional roofing contractor to provide the expertise and specialized equipment to restore the roof’s surface without causing additional harm. And if they determine the years of weather have taken their toll and a roof replacement is imminent, remember the goal is not just a clean roof but a healthy one.