It’s not uncommon for roofs to develop dark streaks over time. While some of this could be dirt, usually the culprit is algae. Whether your roof is marred by dirt, grime, bird feces or a living organism, it’s important to take specific steps to clean the shingles without causing accidental damage.

Cleaning Algae

If you have stains on your roof that won’t wash off in the rain, it’s likely caused by organic growth. Noticeable streaks and strains are typically caused by a type of algae called Gloeocapsa magma. Often appearing gray or black, these stains are quite noticeable on pale-colored asphalt shingles. Although it doesn’t typically cause any physical harm to roofing materials, algae can turn it into an eyesore.

There’s also another type of growth that can damage roofing. Known as fire moss, this type of organic growth is less common than Gloeocapsa magma. When it does occur, however, the moss can dislodge shingles, allowing water to migrate beneath them where it can enter a home’s attic.

Whether your roof stains are caused by moss or algae, you need to use a special solution to kill the organic growth in the following manner:

  1. Create a solution of 50% bleach and 50% water inside a spray bottle.
  2. Access your roof using a ladder and spray the shingles with the solution.
  3. Allow the solution to sit for approximately 15 minutes.
  4. Rinse the shingles using a low-pressure garden hose. Do not use a pressure washer or you could damage your shingles.

Things to Consider

Always check the weather forecast before you get started to make sure there will be no rain or wind. It’s also better if the weather is cool, so the bleach will have more time to work against the algae before the solution evaporates. With this in mind, consider working early in the morning or later in the afternoon.

Since bleach can kill vegetation, it’s important to cover underlying plants and grass before you get started. You should also move flower pots and patio furniture to protect them from runoff or bleach splatter.

Before you get started, it’s also best to clean out your gutters and downspouts to make sure they will drain properly. You should also inspect your roof and fix any loose shingles or flashing. After you’ve cleaned the bleach from your shingles, water your lawn to dilute any potential bleach runoff so it won’t harm your grass.

After you’ve eliminated the organic growth, you should make an effort to prevent a recurrence. Try adding a 6-inch-wide strip of zinc or copper beneath the row of shingles closest to the peak of your roof. Always leave an inch or two of the lower edge exposed so rain can flush some of the metal molecules down the shingles where it will poison any algae spores trying to establish themselves on your lower roof.

A Word of Caution

sodium hypochlorite

You can also purchase roof cleaning detergents designed to kill algae. These contain a chemical called sodium hypochlorite. Before you apply the solution, be sure to dilute the cleanser based on the manufacturer’s guidelines to avoid damaging your roof or underlying vegetation.

When rinsing your roof, be sure to always use a low-pressure garden hose. You should also gently splash the shingles to keep from loosening the roofing granules.

Bear in mind that impatient homeowners often suffer falls when working on extension ladders. It’s also very easy to accidentally damage shingles with just a few missteps. When this happens, water is able to seep into attics, where it spurs mold infestations that lead to thousands of dollars in repair costs.

The Bottom Line

If the organic growth on your roof is extensive, you may ultimately need to replace your roof. In this case, you should consider selecting dark shingles to help conceal any future growth. You can also install shingles equipped with copper granules designed to prevent organic growth.

While you’re on your roof, carefully inspect it to see if you notice any loose or torn shingles or flashing. Even the smallest amount of damage can result in expensive mold infestations. With this in mind, always contact a professional roofing contractor to repair existing damage, no matter how small.

A locally owned Colorado company, A to Z Roofing specializes in reliable residential roofing and repair. A trusted, reputable contractor, we’ve been operating continuously all throughout the Front Range for nearly three decades, serving the needs of Colorado residents and business owners. Contact our team of skilled professionals to learn how we can restore, repair or replace your damaged or aging roof.