How do I Remove Mold, Moss, and Algae Off of My Roof

When the blue-green algae start forming on roof surfaces, it often means trouble. Moss growth on roof shingles can make your cottage in the woods or house look like a fairy tale, but it is more like a nightmare.

If you don’t treat them fast, moss and algae can cause fast degradation to any roofing material. This is a common problem in San Antonio, where asphalt shingles are the most common material.

Even if your root has zinc or copper strips, mold will not care. You may be wondering why your roof has such a short lifespan – well, it’s moss.

Luckily, you can use a moss remover and a cleaning agent like chlorine bleach to clear the problem and keep the roof surface clean. This guide will share simple roof moss removal steps from asphalt shingles and other materials.

Why Do You Need to Remove Green Moss?

Most begins easily like a green layer on the singles or between the roofing materials. It then extends deeper, letting water slip underneath. This creates a perfect condition for wood rot and leaks.

Leaving it to extend too far will force you to replace your entire roofing system. Once mold builds on your shingle roof, be sure the whole house will be affected.

Algae stains spread from the roof deck to other parts of the house. Like most plants, algae or moss produce spores. The moss spores are spread through the air and can easily cover your entire roof.

As you may have already guessed, these plants will destroy your perfect home, starting from the roof plane. Luckily, removing moss is not hard, but a perfect solution to ensure it never happens again.

How do I Remove Mold, Moss, And Algae Off of My Roof – A Step-By-Step Guide

Now that you know why the process is crucial, it’s time we went through the removal steps. For this task, you will need the following:

  • A large spray bottle or pressure washer, or garden hose.
  • A moss removal solution (you can use a DIY bleach solution)
  • A safety rope to hold you steadily on the roof
  • Rubber gloves
  • A spray nozzle
  • A soft bristle brush

Step 1: Gently hose and brush off the moss from the shingles

Start by placing a ladder where the moss grows. Always wear slip-resistant shoes, some old clothes, and other safety gear, and then strap yourself securely in place with the rope.

Working on a dry roof with fewer tree branches hanging over it is much easier. We, therefore, recommend doing this activity on a clear day.

Use a leaf blower to get rid of leave or other dirt that might be on the roof. Then use plain water to hose off moss from the area. Ensure the hose is facing at a downward angle.

Use a long-handled soft brush to lightly scrub off the moss, algae, or mold. Don’t scrub, scour or use too much to remove moss from roof shingles. This can rip, crack or break the materials forcing you to spend more on replacement.

Never use a pressure washer, as it can cause permanent damage to the shingles with its high-power water jets. Even though algae growth is not very pleasing, removing it carelessly is not a good idea. You may not have the budget to get new shingles just yet.

Step 2: Apply cleaning solution

Now you are ready to use your bleach solution to clear the remaining moss. Ensure you have the right chemical solution for this process, whether store-bought or DIY. Some bleach mixtures may not be very friendly to the shingles and plastic sheeting if you have any.

Here are the most common solutions:

Chlorine bleach

There are a few ways of effectively removing moss, algae, and mold, and chlorine bleach are among the best. TSP and chlorine chemical solutions offer the most attractive results. It not only removes the plants but also keeps the affected area clean.

Using bleach mixtures

The bleach mixture will remove algae and moss effectively, but it’s not friendly to other plants. So, you need to use clean water immediately after applying the mixture.

Do not leave the bleach mixture on the roof for more than the recommended time. This could damage shingles and the surface ground. If well done, it can cause minimal damage.

Running water is the best for such projects compared to standing water. Therefore, ensure your hose is ready and you have enough water for the job.

Other chemicals

You need to ensure the chemical solution you are using is safe. The idea is not only to clean but also to prevent moss from growing back.

Sodium hydroxide contains lye, which is more dangerous than bleach. It would be best to avoid using such for algae moss removal projects.

Some people use more customized chemicals, which are also quite effective. However, you must still be careful how and when you spray such chemicals. Caring for the environment should be a priority.

Bleach-free chemicals

The best long-term solution for green algae and mold is bleach-free chemicals. A good example is Spray and Forget, a new, slow-acting product that prevents mildew growth and many years. These chemicals will give you a dry roof since you don’t need to use water to rinse them off.

Step 3: Rinse

Get back on the ladder and rinse off the solution and the dead moss. Use a soft brush to remove any remaining moss, and then rinse the roof using clean water.

How To Prevent Future Mold Growth

Here are some tips you can use to keep the mold away for a long time.

Use algae-resistant roofs

Where algae (Gloeocapsa magma) grows, moss grows there too. They thrive in the same conditions. Material like trisodium phosphate is quite effective in resisting such growth.

Install zinc or copper strips

Installing zinc and copper strips on the roof ridge near the lower gutter discourages moss growth. The strip oxidizes over time to wash down the roof plain when the rain falls.

Regular maintenance

Moss, algae, and mold thrive when a roof is left unchecked for a long time. North-facing roofs are in much better condition since they can leverage the sun’s rays, keeping the roof dry most times, but most can still thrive on a cloudy day or season. So, keep your roof in check at all times.


Roof moss and green algae can threaten the integrity of your home. We, therefore, recommend removing it as soon as possible. Call your roofing experts at Bison Roofing, and you can forget all those issues.