Black streaks running down your roof ruin curb appeal fast. These stains aren’t just dirt; they are likely a hardy algae called Gloeocapsa magma feeding on the limestone filler in your shingles. You might assume you need a professional crew, but you can tackle this project yourself.
Here is how to clean a shingle roof safely and effectively.
Key Takeaways
- The best DIY mix: Use a 50:50 blend of household chlorine bleach and water to kill algae and mold.
- Application method: Apply the cleaner with a garden sprayer and let it sit for 20 minutes before a gentle rinse.
- Pressure washer warning: Never use high pressure on asphalt shingles; it strips granules and voids warranties.
- Prevention: Install zinc or copper strips near the roof ridge to prevent future algae growth.
What Is the Best Cleaner for Roof Shingles?
You have three main options when choosing a cleaner for asphalt shingles.
1. Chlorine Bleach and Water
This is the industry standard for “soft washing.” Sodium hypochlorite (bleach) kills the algae and moss spores instantly. It is cheap, effective, and accessible. You simply mix it with water.
2. Commercial Spray-and-Leave Products
If you prefer pre-mixed solutions, products like Spray & Forget or Wet & Forget are excellent. You spray these on the roof and let rain wash the decay away over time. These take longer to show results but require less labor.
3. Oxygen Bleach
For a more eco-friendly approach, you can use oxygen bleach (sodium percarbonate). It is safer for plants but generally less potent than chlorine bleach against heavy moss infestations.
Is It Safe to Pressure Wash a Shingle Roof?
No, you should never pressure wash an asphalt shingle roof.
Pressure washers operate at high PSI levels that blast away the protective ceramic granules on your shingles. These granules protect the asphalt from UV rays. Losing them accelerates the aging process and can lead to leaks.
Professional roof cleaners use a method called “soft washing.” This involves applying a cleaning solution at low pressure (similar to a garden hose) and letting the chemicals do the work rather than mechanical force.
Will Bleach Damage Roof Shingles?
No, a diluted bleach solution will not damage asphalt shingles when used correctly.
Most shingle manufacturers, including GAF and Owens Corning, recommend a mix of bleach and water for cleaning. However, straight undiluted bleach is too harsh. It can corrode metal flashings and damage your gutters. Always stick to the recommended 50:50 ratio and rinse thoroughly.
How to Clean Roof Shingles
Roof cleaning is dangerous. Safety is your priority. If your roof has a steep pitch or is more than one story high, consider hiring a professional.
- Time: 2, 4 hours
- Difficulty: Advanced
What You’ll Need
- Full-body safety harness
- Non-slip shoes (soft sole)
- Sturdy extension ladder
- Safety goggles and gloves
- Garden hose with spray nozzle
- Pump-style garden sprayer
- Household bleach (or commercial cleaner)
- Plastic sheeting (for plants)
1. Prioritize Safety
Wait for a cool, overcast day with little to no wind. Wind can blow chemicals back into your face, and hot sun evaporates the cleaner too quickly.
Wear your safety harness and secure it to a strong anchor point. Wear non-slip shoes with good traction. Moss is incredibly slippery when wet, so walk carefully.
2. Prepare the Area
Bleach kills plants. You must protect your landscaping before you spray a single drop:
- Move furniture: Clear patio furniture and decor away from the drip line.
- Soak the soil: Thoroughly water all plants, bushes, and grass around the house. When plants are already saturated with water, they are less likely to absorb the bleach runoff.
- Cover up: Cover delicate shrubs with plastic sheeting.
3. Mix the Solution
Pour water and household chlorine bleach into your garden sprayer. A 50:50 ratio is standard for tough stains. If the stains are mild, you can try a mix of 75% water and 25% bleach.
Secure the lid tightly and pump the sprayer to build pressure.
4. Apply to the Roof
Start from the top of the roof and work your way down. This prevents the solution from running over areas you haven’t treated yet and creating streaks.
Spray every shingle until it is thoroughly wet. Focus heavily on areas with visible moss or black algae streaks. Let the solution sit on the surface for 15 to 20 minutes. Do not let it dry completely; mist it with a little water if necessary to keep it active.
5. Rinse Gently
Use your garden hose to rinse the roof. Start from the top and spray downward toward the gutters. Never spray up under the shingles, as this can force water into the decking.
The algae should wash away easily. If you have thick moss, it may not detach immediately. The chemicals will kill the moss, and it will eventually weather off over the next few weeks. Do not scrub aggressively, as this damages the granules.
Once you finish, immediately uncover your plants and water them generously again to dilute any chemical runoff.
How to Prevent Algae Regrowth
Once your roof is clean, keep it that way with these preventative measures:
- Install zinc or copper strips: Place these metal strips under the ridge cap of your roof. Every time it rains, metallic ions wash down the roof, creating an environment where algae cannot survive.
- Trim overhanging branches: Algae and moss thrive in damp, shaded areas. Trimming trees allows sunlight to dry the roof surface, making it inhospitable for growth.
- Clear debris regularly: Leaves and pine needles trap moisture. Clean your roof valleys and gutters twice a year to promote proper drainage.
FAQs
Does Cleaning Prolong the Life of a Roof?
Yes, removing algae and moss can extend your roof’s lifespan. Moss roots lift shingles, allowing water to seep underneath and rot the wood decking. Black algae absorbs heat, keeping your attic hotter and breaking down the shingles faster.
Why Should You Remove Algae From a Roof?
You should remove algae because it eats the limestone filler in your shingles. While primarily an aesthetic issue initially, unchecked algae growth invites moisture retention and can eventually compromise the integrity of the roof material.
How Do You Clean a Roof Without Damaging the Shingles?
The key is avoiding pressure. Use a chemical solution (like bleach and water) to dissolve the dirt and organic growth, then rinse gently with a garden hose. Never use a wire brush or a pressure washer.
Does Spray and Forget Work on Roofs?
Yes, Spray & Forget is effective for killing algae, moss, and mildew on roofs. It is a “no-rinse” cleaner, meaning you apply it and let the rain wash the debris away over time. Note that it works slower than bleach.
What Time of Year Should I Clean My Roof?
Summer or late spring is the best time to clean a roof. The dry, warm weather makes the work safer and ensures the cleaning solution activates properly. Avoid freezing temperatures, as water can freeze on the shingles and cause slip hazards.
How Do You Remove Mold and Mildew From Roof Shingles?
Apply a 50:50 mixture of water and household bleach. Let the solution soak into the mold for about 20 minutes, then rinse thoroughly with a low-pressure hose. The bleach kills the spores on contact.
Is Soft Washing a Roof Worth It?
Absolutely. Soft washing is the safest method for cleaning asphalt shingles. It removes unsightly stains and damaging organisms without stripping the granules or voiding your roof warranty.
How Often Should You Clean Your Roof?
You typically need to clean a roof every 3 to 5 years, depending on your climate and the amount of shade your roof receives. If you live in a humid area with many trees, you may need to clean it more frequently.
