How To Remove Mold From Your Roof

November 4, 2015

Does your roof have black streaks streaming down your asphalt shingles? Or perhaps there’s a green growth that looks sort of mossy on your roof? If you have either of those coloration issues, you probably have roof algae or mold on your roof shingles. This mold will not only discolor your roof, but can also damage your shingles over a long period of time if you do not remove it.

Why Does Algae and Mold Happen?

These streaks tend to only appear in certain areas of the country, specifically, the humid areas. And, strangely, the streaks typically only appear on the north side of the roof.

But why does this happen?

These streaks of algae/mold start growing on your roof through airborne spores. The reason it typically grows on the north side of your roof rather than the south side of your roof is because the north side gets the least amount of sun, making that part of the roof the one that stays the dampest the longest when it rains. The limestone filler in shingles is what the algae feeds on and these spores can spread throughout an entire neighborhood easily through the air.

How to Remove Mold or Algae from the Roof


Mold on your roof can be easily removed with basic household bleach. Below, we’ll explain exactly how to do this.

Before you get started on removing the mold or algae, make sure to protect your lawn from the bleach solution. The best way to do this is either to cover the plants or parts of your lawn that are close to the house with a tarp. If you cannot manage to do that, make sure to at least splash the plants and parts of your lawn that are close to the sides of your house with water. The water will protect your plants and lawn from the bleach solution.

Next, you’ll need to make and apply the bleach solution!

Grab a large bucket from your house, preferably a 2 gallon one. Then grab some chlorine bleach and water as well as some trisodium phosphate, otherwise known as TSP. You’ll need to make sure that the solution is a quarter of chlorine bleach and three quarters water. Then add one tablespoon of the TSP. Put the solution in a spray bottle and then get yourself set up on the roof. Make sure there is someone at the bottom of the ladder that you can call for help if you’re having problems getting up or down on the roof. If your problem is mold, make sure to also bring a brush to scrub off the mold as best you can.

Next, apply the solution! You’ll need to make sure you’re wearing gloves of some kind, rubber ones are fine. Then spray the solution onto the moldy shingles – and only the moldy shingles. Try not to get the solution on the shingles that aren’t moldy.

Once that is done, you should wait for about 15-20 minutes to allow the solution to soak into the shingles. Then, rinse the shingles off slowly. You can do this with a garden hose at low pressure, a small bucket, or a spray bottle filled with water. Either way, start from the top shingle and allow the water to rinse downward. This prevents water from seeping into the shingles and causing more problems. After you do this, check out the shingles. Make sure you got all of the mold.

If there is mold leftover, you’ll need to repeat the solution and rinse it off again.


It’s better if you DON’T use a pressure washer to rinse off the shingles. This can hurt the integrity of the shingles and reduce their ability to repel water, eventually causing leaks inside your home. Try to just use a garden hose at low pressure, that should work just fine.


After doing this, you will probably want to prevent it from happening again. There is one way to do this. Insert 6 inch strips of zinc or copper under the row of shingling that is closest to the roof peak. This allows for some of the metals to wash down the roof anytime it rains and kill any mold that’s attempting to grow on your shingles. Copper flashing on chimneys could also work.

At Accord Construction, we want to make sure your roof is beautiful, safe, and structurally sound. No matter if you’d like to arrange a roof inspection or need your roof to be redone, we’re ready to help. Our company is fully licensed and certified, just call us at (405) 302-5520 if you’d like to arrange a consultation.

Get a Free Estimate