Are you noticing visible stains on your roof, such as black streaks or patches of green? This often happens on roofs covered in asphalt shingles, although it can happen on other types of shingles, like cedar shakes. It usually means algae or moss are growing on your roof.

Cleaning your roof will make your home look better for your own enjoyment, as well as improving curb appeal if you’re planning to sell. At the same time, it may save you money because the moss and algae that cause roof stains can damage your shingles, shortening their life and exposing your home to moisture.

You may want to clean it yourself to save money or to learn how to clean a roof. If you’re in the do-it-yourself mode, you can use the process below to get it done. But you must use safety precautions to protect yourself whenever you’re on any roof. Many falling accidents occur while working on roofs and ladders.

Dangers of Algae and Moss on a Roof

Why do algae, moss, and single-celled organisms cause stains and damage to a roof? And what causes black streaks on shingles? To understand how to clean your roof, you should first understand what is causing the problem. Here are two common varieties of roof attackers and their effects:

Gloeocapsa Magma: This is a collection of photosynthesizing bacteria that can attach themselves to your shingles, feeding on the limestone there and breaking it down. They cover themselves in a dark substance to limit the amount of sunlight they receive, and that causes dark stains. These algae can then attract fungus and moss, further compromising shingles.
Fire Moss: This moss can grow under the shingles and push shingles up as it grows, which lets water under your shingles and into the wooden structure of your roof, threatening it with damage and decay. Plus, it can curl your shingles until they are blown away by the wind.

You may need to hire a professional to examine your roof and identify the exact organisms growing there. Different culprits require different solutions, and a professional can tell you the type of cleaning substance needed and the length of time it will need to work.

How Can You Clean Your Roof Shingles without a Pressure Washer?

Because algae are attached to individual gravel particles on shingles, pressure washing doesn’t guarantee their removal—and washes away the surface of the shingles that you need. It’s also challenging to remove moss from under shingles.

Many people don’t have pressure washers, and they are not effective solutions, anyway. What is? You can use soft washing (as opposed to pressure washing) instead. That means you use a garden sprayer to gently spread a solution onto your shingles to kill the algae or moss, not to forcibly spray it off.

You will need:

Garden sprayer
Protective clothing
A roof cleaner that includes sodium hypochlorite

Then, go through these steps:

1. Wait for Roof Cleaning Weather

You should clean your roof on an overcast day with little wind and no threat of rain. A hot day will cause your roof cleaning liquid to evaporate too quickly for it to complete its work. A windy day will move shingles and solution around too much. And rain will wash away the solution.

2. Protect Your Yard

Check any gutters you have in advance. See if they empty onto your trees or plants. With a garden hose, soak any plants that may be affected by your roof cleaning solution. This will saturate their cells, preventing them from absorbing the chemicals. An experienced professional will know what these chemicals can do to your plants and how to protect them when needed.

3. Prepare Your Roof Cleaning Solution

Be cautious as you mix a cleaning solution in your garden sprayer. If you or a professional find that your roof hosts fire moss, lichen, or dense algae, you can use a solution of 75% sodium hypochlorite and 25% water.

For gloeocapsa magma, black streaks, or light black algae, use 50% sodium hypochlorite and 50% water. And for light stains, use only 25% sodium hypochlorite and 75% water.

If the solution runs off of your shingles too quickly, you can also add a quarter of a cup of dish soap to make it stick to the shingles longer—and have more time to work on the algae or moss.

4. Work from the Top Down

Start spraying at the ridge of your roof and work down to the edge gradually. Coat every area evenly.

5. Add a Second Coat When Needed

In general, you don’t need very much of your solution in each area. Don’t soak your shingles. But if some patches of algae or moss have not vanished or turned white after your first pass, you can lay down a second coat. If that doesn’t kill it, you can mix a higher solution of chemicals from Step 3 above and apply that. Moss or algae often turns white when dead.

6. Wait

Give the chemicals some time to work on your roof. Use caution when climbing down a ladder. Just check your roof again in 2–3 weeks to see if any problem areas need to be re-treated.

7. Wash Your Plants

Despite our precautions above, your plants may still be damaged by these chemicals. Using your garden hose, rinse off any plants that may have been affected (or all plants in your yard). Don’t let these harmful chemicals do to your yard plants what they are meant to do to algae and moss.

8. Check and Repeat within a Year

Algae and moss can travel through the air between rooftops. If weather conditions have caused them to grow on your roof before, they can grow again. So, mark your calendar for 9–12 months in the future, and inspect your roof again when the time comes. If you’re proactive and clean it before it starts to look bad, less staining and damage will occur.

Call for Professional Roof Cleaning

Although learning how to clean a roof yourself may save money in the short term, you might accidentally damage your shingles or get chemicals on your yard plants. And walking on your roof carries the risk that you could fall. Plus, you might better use your time on your own pursuits.

If you would rather have an experienced technician identify the organisms on your roof and apply the right solution, call DMG Exteriors for roofing work in Lake, Porter, and LaPorte counties in Indiana. Let us use the best roofing technologies on your first line of defense against the weather. Contact DMG Exteriors now.