How to Clean Mold off Roof Shingles

A roof, with leaf-strewn lawn below.
What You'll Need
Plastic sheeting or tarps (optional)
Rubber gloves
Breathing mask
Handheld pump sprayer

Mold stains can form on roof shingles that are in permanent shade. These stains will discolor your roof and damage the shingles over a period of time if left alone. Extensive mold growth can also expose the interior of your attic or crawlspace to mold spores, carrying the problem over to the inside. Not to worry, though, because you can clean the mold off with basic household bleach and save your roof long before you need an expensive replacement. Follow the steps below to remedy this problem.

Protect Your Plants and Lawn

Splash the plants and parts of your lawn that are close to the sides of your house with water to protect them from the bleach solution. You can also cover them with tarps or plastic sheeting, which will protect the soil around your plants as well. Make sure that you create a wide radius around your home to be safe.

Make and Apply the Bleach Solution

Put on rubber gloves and a breathing mask before proceeding, so you can protect your skin and your lungs from the fumes produced by both bleach and trisodium phosphate. In a two-gallon bucket, create a cleanser composed of 1/4 chlorine bleach and 3/4 water. Then, add one tablespoon of trisodium phosphate (TSP) and mix well. Fill a handheld pump sprayer with the solution, and apply it to the moldy shingles only.

Check for Cleanliness and Rinse

Allow the solution to soak into the shingles for at least 15 minutes. If they are severely molded, you may want to give it a little longer. Next, rinse the shingles thoroughly with a garden hose at low pressure. Start from the top shingle and rinse downward to prevent water seepage.

Run your gloved hand over the shingles to check for any slimy mold remaining after you're finished rinsing. If some remain, apply the cleanser again, wait 10 more minutes, and repeat the rinse process.

Take Precautions

Never use a pressure washer to wash or rinse shingles. The concentrated jet will scrape off the small pebbles on top of the shingles and reduce their water repellency, which will only make your mold situation worse.

If you have a consistent problem with mold growth on your roof, consult a roofing professional. Your shingles may be old and in need of replacement, or just in need of waterproof coating to help prevent them from getting too wet.