Your roof is one of the first features a guest will look at when arriving at your home which is why it’s of the utmost importance you not only understand what those stains are on your roof, but how to remove them. Roof stains are can usually be blamed on defective shingles, dirt accumulation, mildew or mold; however the most common culprit of them all is blue-green algae, which is also known as Gloeocapsa Magma – it’s spread by airborne spores. And, although algae will do little harm to your roof, the stains it causes doesn’t help your home’s resale value or its overall appearance.

Charlotte is in a high algae growth area.

There are two areas that are susceptible to algae stains; one is a low algae growth area and the other is a high algae growth area. Charlotte is a high algae growth area which means you may be experiencing the stains we’ve been describing. In fact, the midwest and east coast are the most susceptible to blue-green algae, as well as the Pacific coast.  

What causes the stains?

If you look on your roof and notice that it has been affected by the blue-green algae, it’s probably safe to bet the algae has started to grow directly below metal flashings or around roof vents and chimneys. You can thank the zinc or copper coating that the galvanized sheet metals are made out of which are toxic to algae. What does this mean, exactly? Every time it rains or snow melts, trace amounts of metals leave the flashings and trickle down the roof with the water, inhibiting algae growth.


There are algae resistant shingles.

If you are due for a roof replacement, you may want to think about getting algae resistant shingles. In recent years, manufacturers have begun mixing roofing products with copper granules to produce shingles that are algae resistant. So, if your roof has experienced the blue-green algae plague, this might be a good idea that you’ll want to think about.

How to remove blue-green algae using chemicals.

If you’re not due for a new roof for some time, feel free to remove the algae build up using chemicals. Although they can be removed, it’s likely they’ll eventually return. While cleaning your roof with a chemical occasionally won’t be damaging to your roof, repeated harsh chemical use can be by creating an erosive effect of pressure washing. Doing so too often will shorten the life of the asphalt shingles. However, there are several products available that were specifically designed to keep your roof intact and remove algae stains. These products are usually made with a mixture of water, bleach and trisodium phosphate (TSP).

Items you’ll need to remove algae include:

  • Cleaner
  • Pump sprayer
  • Garden hose with spray nozzle
  • Safety glasses or goggles
  • Rubber gloves
  • Safety rope
  • Old clothes
  • Slip resistant shoes
  • Ladder

Safety First!

Remember, safety should be your number one priority! Working on a roof is always a dangerous job, and it is even more so when the roof is wet. If your roof is steep or you don’t have slip resistant shoes, call a roof repair professional for help instead. Also, keep your skin and eyes safe by wearing gloves and eye protection. Keep in mind, plants are not safe from these chemicals. If the roof is wet and the bleach runs off the roof onto grass or plants below, it’s likely they will die; cover the ground below with a plastic sheet and wash the plants and grass after you spray the roof.

Start removing the algae.

We suggest cleaning your roof on a cloudy day. Why? Doing so will help to prevent the mixture from evaporating too quickly. If you know what company manufactured the shingles on your roof, give them a call to learn if they have any guidelines or tips for removing algae; they may have a product made for the specific type of asphalt shingle.

Using a garden sprayer, thoroughly spray the roof with the chemical solution and allow it to soak in for 15 minutes. After the 15 minutes has passed, rinse off the roof with a hose.

How to prevent algae growth.

Keeping your roof free of algae can be challenging if you live in Charlotte, but our roof repair experts can help! Our roof repair experts can install at a strip of zinc or copper coated sheet metal along the tip of the roof and the sides. Doing this can significantly decrease your roof’s chances of algae growth. Take note, though, because 2 to 4 inches of metal will be visible.

Want to learn more?

Our roof repair experts here in Charlotte know a lot about the blue-green algae growth problem. Contact our professionals online today or give us a call at (704) 755-4046. We have the solutions you need. Reach out to us today and stay tuned for our next blog post.