If you’ve noticed dark, black, or blue-green streaks appearing across your asphalt shingles, you’re not alone. Those stains are extremely common on residential roofs, particularly in areas with warm, humid conditions like East Tennessee. While they can make a roof look older than it actually is, those dark streaks are often caused by blue-green algae, a type of cyanobacteria known as Gloeocapsa magma. The good news? Homeowners have options for addressing algae staining and maintaining their roofs. GAF, one of the country’s leading roofing manufacturers, offers several recommendations for cleaning and protecting asphalt shingles. Here are some important roof maintenance and cleaning tips from GAF that homeowners should know.
What Are the Black Stains on Your Roof?
Those dark streaks running down your shingles may look like dirt, mold, or general discoloration, but they are often caused by blue-green algae. Gloeocapsa magma can spread from one roof to another through airborne spores. When those spores land on a roof, they can begin to grow when the right conditions exist. The dark appearance comes from a protective sheath produced by the algae. This sheath helps protect the organism from ultraviolet radiation, which is one reason the staining can become increasingly noticeable over time. Algae staining often appears more heavily toward the lower portions of a roof and may gradually taper as it moves toward the ridge.
Why Does Blue-Green Algae Grow on Roof Shingles?
Like many forms of organic growth, blue-green algae needs moisture and suitable temperatures to thrive. One of its primary sources of moisture is dew. Roof areas that receive less direct sunlight can also be more susceptible to algae growth. That’s why homeowners may notice more staining on northern-facing roof slopes or areas that remain shaded for longer periods of the day. Blue-green algae is also remarkably adaptable. It can grow across much of the United States and Canada, meaning algae staining isn’t limited to one particular region or climate. In other words, seeing dark streaks on your roof doesn’t necessarily mean there’s something wrong with your shingles. It can simply be a sign that the environmental conditions around your home are favorable for algae growth.
Should You Be Worried About Algae Stains?
Algae staining is primarily a cosmetic concern, but it shouldn’t be completely ignored. A roof covered in dark streaks can detract from your home’s appearance and make the shingles look older or more weathered. More importantly, noticing algae, moss, or other growth is a good reason to take a closer look at the overall condition of your roof. A professional roof inspection can help determine whether you’re dealing with simple staining or whether there are other maintenance issues that need attention. That’s especially important if your roof is several years old or you haven’t had it inspected recently.
How Should You Clean Algae From Roof Shingles?
GAF recommends a specific cleaning solution for removing blue-green algae discoloration from asphalt shingles.
According to GAF’s guidance, the recommended mixture consists of:
- 4 gallons of water
- 1 gallon of bleach
- 1 cup of TSP (trisodium phosphate), or an acceptable phosphate-free substitute
The mixture can be applied using a garden sprayer. GAF recommends allowing the solution to remain on the roof surface for up to 20 minutes, followed by rinsing with low-pressure water. There are some important safety considerations, however. The cleaning solution can affect surrounding landscaping, so shrubs and other plants below the roof should be protected before cleaning begins. Additionally, the roof surface can become extremely slippery when wet. For those reasons, homeowners should carefully consider whether roof cleaning is a project they should tackle themselves.
Whatever You Do, Don’t Power Wash Your Shingles
This is one of the most important roof-cleaning recommendations homeowners should know. Don’t power wash asphalt shingles.
It may seem like pressure washing would be the quickest way to remove those black streaks, but high-pressure water can potentially dislodge the protective granules from your shingles. Those granules play an important role in protecting the asphalt shingles from the elements. Removing them can contribute to premature deterioration and reduce the expected service life of the roof. Some roof cleaning companies may offer pressure washing as part of their services, but GAF specifically advises against power washing shingles. If your roof needs to be cleaned, the cleaning method matters just as much as the cleaning product.
Consider Algae-Resistant Shingles When Replacing Your Roof
If you’re already thinking about replacing your roof, algae resistance is another factor worth considering. GAF offers several shingle products with algae protection designed to help reduce blue-green algae discoloration. Some GAF shingles feature StainGuard Plus PRO™ Algae Protection, while others are available with StainGuard Plus™ or StainGuard® Algae Protection. GAF’s algae-resistant shingles use algae-fighting technology designed to provide protection against blue-green algae discoloration over time. Innovative Roofing is a GAF Master Elite partner, but please note that available products and warranty coverage can change. Homeowners should review the current GAF product information and applicable warranty documentation when selecting shingles. For homeowners who live in an area where algae staining is common, choosing algae-resistant shingles can be an important consideration during a future roof replacement.
Regular Roof Maintenance Can Help You Catch Problems Early
A yearly roof inspection allows a professional to look for issues that may not be obvious from the ground, including:
- Missing or damaged shingles
- Damaged flashing
- Deteriorating sealants
- Problems around roof penetrations
- Accumulated debris
- Drainage concerns
- Signs of moisture intrusion
- Algae, moss or other organic growth
- General shingle deterioration
Catching these issues early can give homeowners more options than discovering a problem after a major leak develops. Roof cleaning can also be incorporated into a broader maintenance plan when appropriate. A professional roofing contractor can determine whether cleaning is necessary, what method is appropriate, and whether there are underlying roofing concerns that should be addressed first.
A Clean Roof Is Only One Part of Good Roof Maintenance
Those black streaks may be the first thing you notice, but they’re not the only thing worth paying attention to. Your roof is constantly exposed to rain, wind, sunlight, humidity, and changing temperatures. Regular inspections and appropriate maintenance can help you stay ahead of potential problems and better understand the condition of your roofing system. If you’re noticing black streaks on your roof, algae staining, or other changes in the appearance of your shingles, don’t automatically assume you need a new roof. A professional inspection can help determine whether the issue is primarily cosmetic or whether there are additional concerns.
Need Help Maintaining Your Roof?
Innovative Roofing & Siding can help homeowners understand what’s happening with their roof and determine what type of maintenance may be appropriate. Whether your roof needs an inspection, cleaning, or more extensive repairs, getting professional advice can help you avoid unnecessary work while addressing legitimate roofing problems before they become more expensive. Contact Innovative Roofing & Siding, your local GAF Master Elite roofing company, to schedule a professional roof inspection and find out what your roof needs to stay in good condition.