How to Remove Algae and Mold From Roof Shingles


How to remove algae and Mold from Roof Shingles

When your roof is healthy and in good condition, it’s part of the overall tidy appearance of your home. However, in humid climates like West Michigan, moisture often produces unsightly black algae streaks that form on the roof and make it look dirty. To keep your roof strong and maintain your home’s appearance and resale value, there are a few steps you can take to refresh your roof and remove roof stains.

Difference between Mold, Moss and Algae

Mosses, algae, and mold on the roof share a common love for moisture, but the organisms are all quite different.


Algae stains on a shingle roof

Algae stains on a shingle roof

What we see most often in West Michigan are the flat, dirty black streaks produced by algae on the roof. The most common type of roof algae is gloeocapsa magma or blue green algae. Gloeocapsa magma is an algae form that spreads by air and by animals, and can grow from a small spot to long streaks in a matter of months. Although the algae is not necessarily damaging to an asphalt shingle roof, according to the Asphalt Roofing Manufacturers Association, it is certainly unattractive.


Moss on a shingle roof

Moss on a shingle roof

Moss is a non-vascular plant that is fluffy compared to algae, and may appear green, grey, blue, or brown. Generally moss finds a home in moist and shaded areas, often on parts of the roof that are north-facing or are shaded by trees. The moss itself is harmless to humans, but it can damage your asphalt shingles and cause them to curl up, so it needs to be removed.


Man examining roof mold

Man examining roof mold

Mold is caused by spores that travel on the wind, or may be tracked by squirrels and birds around the neighborhood. These mold spores most often take hold in areas of the roof that are already moist, like penetrations through the roof deck around chimneys or places where moss has already damaged the shingles and created a damp environment.

How to Remove Roof Stains and Moss

Depending on your roof and your comfort level with a ladder, you can often remove algae and moss on the roof with a straightforward procedure involving bleach and water, a spray bottle, a hose, and a ladder.

Choose the Right Day to Clean Your Shingles

The cleaning solution may evaporate too quickly on a sunny day, so a cloudy day is normally best for cleaning your roof.

Prepare Your Solution

A number of chemical solutions available in the hardware store are designed to remove algae from roof systems. However, it can be just as effective to go with chemicals you already have at home that are known to remove algae and moss – namely, bleach or oxygen bleach. A 50/50 solution of water and laundry strength chlorine bleach or oxygen bleach can be mixed and applied with a spray bottle. For an even stronger cleaning solution, add ½ cup per gallon of trisodium phosphate.

Ensure Roof Safety

Whenever working on a roof, bear in mind that roofs are potentially dangerous – even more so when wet. Wear a safety harness or at least some slip-resistant shoes, and avoid steep pitches. You’ll also want to wear some eye protection to protect them from chemicals.

Protect Your Home and Plants

Just as the organisms on your roof won’t thrive in bleach, your plantings around your house won’t like it either. To minimize damage to your lawn, shrubs, flowers, and trees, spray them with a nice rinse of water before you start on the roof. You may even want to cover them up with plastic sheeting. And when you’re finished with the roof, spray the plants well one more time to rinse away as much of the runoff as you can.

Remove the Roof Algae and Moss

Apply your bleach solution with a sprayer bottle, and let it rest for 20 minutes or so. If you leave the solution on too long, it can dry and cause damage to the roof. After the solution has had a chance to do its job, rinse off the roof with the hose. Most of the moss and algae will probably be removed with the rinse water. Although some moss may remain, and it will likely continue to wither and be washed away with the rain.

Things to Avoid When You Remove Roof Stains

It may be tempting to use a pressure washer, but the high pressure of the water carries the risk of stripping away the granules in the asphalt shingles, causing premature roof wear. If you still have algae and moss after you clean your asphalt shingles, you can try the procedure a second time. Just make sure to completely rinse the solution if you use bleach.

How to Get Rid of Roof Mold

Roof mold can be a little trickier to tackle than algae and moss. To get rid of mold, you can try a similar process to remove the stains, but there is often underlying damage. An attic and roof inspection can help identify the cause of roof mold. Because of the health hazards of black mold and the possibility that the roof damage is a symptom of a bigger problem, mold removal efforts are often best left to a professional who knows how to remove mold from asphalt shingles and address any underlying issues.

When to Call in a Roofing Contractor

Moss and algae growth may be unappealing, but they are generally a fairly simple problem for a homeowner to tackle. Whenever you suspect shingle problems as a result of algae or mildew, or if mold problems may be lurking, contact Melvin Belk Roofing for a free roof inspection! We service the Grand Rapids MI area and its neighboring communities in West Michigan.

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