If your roof has dark streaks, green growth, or accumulated debris, you may be wondering how to clean asphalt shingles without causing damage. Asphalt shingles are designed to protect your home from rain, snow, wind, and sunlight, but they can develop algae, moss, dirt, and other buildup over time.
Knowing the right cleaning methods can help you maintain your roof’s appearance without unnecessarily damaging the shingles. Before you reach for a pressure washer or climb onto your roof, learn which methods are recommended and which can cause problems.
If your roof needs professional attention, contact Bak Brothers, Inc. at 224-332-2778 for help with your roofing needs.
Why Do Asphalt Shingles Get Dirty?
Asphalt shingles are exposed to the elements year-round. Rain, snow, wind, sunlight, falling leaves, and changing temperatures can all contribute to the gradual accumulation of dirt and debris.
Environmental conditions can also create an ideal environment for algae and moss. Roofs with limited sunlight, nearby trees, and prolonged moisture exposure are particularly susceptible.
Common causes of roof discoloration and buildup include:
- Algae growth
- Moss growth
- Leaves and pine needles
- Dirt and dust
- Tree branches and organic debris
- Excess moisture
- Shaded areas
- Poor water drainage
Understanding the source of the buildup is important because algae, moss, and ordinary debris should not necessarily be handled in the same way.
For homeowners considering a new roofing system, understanding asphalt roofing systems can also help explain why proper maintenance matters.
Algae vs. Moss: What’s Growing on Your Roof?
One of the first steps in learning how to clean asphalt shingles is identifying what is actually growing on the roof.
Roof Algae
Dark black or brown streaks are commonly caused by algae. According to the Asphalt Roofing Manufacturers Association, algae discoloration can appear as streaks or dark areas on asphalt roofing and is particularly noticeable on lighter-colored roofs.
Although algae can make a roof look dirty or aged, ARMA notes that algae discoloration itself has not been shown to affect the service life of asphalt shingles.
That doesn’t mean the stains should be ignored. They can affect curb appeal and may indicate that the roof is exposed to the moisture and environmental conditions that encourage biological growth.
Moss on Roofs
Moss is different from algae and can create more significant concerns for asphalt shingles.
Moss requires moisture to survive and commonly develops on shaded roof areas. According to ARMA’s guidance on algae and moss prevention, moss can cause shingle edges to lift or curl and can interfere with the roof’s ability to shed water properly.
If you see substantial moss on your roof, don’t aggressively scrape it away. Improper removal can damage the shingles underneath.
How to Clean Asphalt Shingles Safely
The safest answer to how to clean asphalt shingles begins with avoiding aggressive cleaning techniques.
Asphalt shingles contain protective mineral granules that help protect the roofing material from weather and ultraviolet exposure. Scrubbing, brushing, or pressure washing can loosen these granules.
ARMA recommends using gentle cleaning methods and specifically warns against power washers and abrasive brushes when cleaning asphalt roofing. Its technical guidance on keeping asphalt roofs clean explains that aggressive cleaning can remove granules from the shingles.
1. Check the Shingle Manufacturer’s Instructions
Before you clean asphalt shingles, determine what type of shingles are installed on your home and check the manufacturer’s recommendations.
Cleaning instructions can vary depending on the roofing product. The manufacturer may provide guidance regarding:
- Approved cleaning solutions
- Proper dilution
- Application methods
- Dwell time
- Rinsing
- Safety precautions
- Warranty requirements
This step is especially important if your roof is relatively new or still covered by a manufacturer’s warranty.
If you’re unsure what type of roofing system you have, a professional roofing contractor can help identify the material and recommend the appropriate maintenance approach.
2. Remove Loose Debris Carefully
Leaves, pine needles, branches, and other debris can collect on asphalt shingles and hold moisture against the roofing surface.
Loose debris should be removed using a non-abrasive method rather than scraping or aggressive brushing. ARMA recommends using a leaf blower or similar method and directing airflow down the slope of the roof to prevent debris from getting underneath the shingles.
However, homeowners should consider the safety risks before attempting this themselves. Even a roof that appears relatively flat can become dangerous when wet or covered with algae.
If you are already concerned about your roof’s condition, scheduling a professional roofing inspection is a safer option than climbing onto the roof yourself.
3. Use an Appropriate Cleaning Solution
For algae and moss, an appropriate cleaning solution may be used to treat the affected areas.
ARMA’s guidance describes a diluted liquid chlorine bleach solution for certain asphalt roofing cleaning applications. However, the exact solution and concentration should always be determined according to the shingle manufacturer’s recommendations.
The solution should be applied gently rather than scrubbed into the shingles.
Take precautions to protect:
- Landscaping
- Siding
- Windows
- Doors
- Vehicles
- Walkways
- Other surrounding surfaces
Always follow the cleaning product’s label directions and use appropriate personal protective equipment.
4. Allow the Solution to Work
Cleaning solutions need sufficient time to work against algae and other biological growth.
ARMA’s current technical bulletin recommends allowing its specified cleaning solution to remain on the roof for at least 15 minutes but no more than 20 minutes before gently rinsing it with water. It also warns that the process can make the roof extremely slippery.
Don’t assume that the same dwell time applies to every cleaning product. Always follow the instructions associated with the specific product and roofing system.
5. Rinse With Low Pressure
After the recommended dwell time, the cleaning solution should be rinsed from the roof using low-pressure water when appropriate.
The goal is to remove the solution without damaging the asphalt shingles.
This is where many homeowners make a costly mistake.
Do not use a pressure washer.
ARMA specifically warns that high-pressure washing can damage asphalt roofing and cause granule loss.
What Not to Do When You Clean Asphalt Shingles
Knowing what not to do is just as important as knowing how to clean roof shingles.
Avoid these common mistakes:
- Do not pressure wash asphalt shingles.
- Do not scrub the roof with a stiff brush.
- Do not scrape moss aggressively.
- Do not use an unapproved chemical cleaner.
- Do not ignore the manufacturer’s instructions.
- Do not allow cleaning chemicals to damage landscaping.
- Do not walk across wet or chemically treated shingles.
- Do not assume every dark stain is dirt.
ARMA warns that the cleaning process can make an asphalt roof extremely slippery. Its guidance recommends that trained professionals handle this type of work because of the fall risk.
If you discover damaged or deteriorating shingles while inspecting the roof, cleaning may not be the only issue that needs attention.
Why Pressure Washing Asphalt Shingles Is a Bad Idea
Pressure washing may seem like the fastest way to clean a dirty roof, but it can cause expensive damage.
The force of high-pressure water can loosen the mineral granules embedded in asphalt shingles. These granules provide an important protective layer against the elements.
Pressure washing may also:
- Damage the surface of shingles
- Remove protective granules
- Force water into vulnerable areas
- Damage older or weakened shingles
- Shorten the useful life of the roofing system
For these reasons, asphalt roof cleaning should use gentle methods instead of high-pressure equipment.
If a contractor recommends pressure washing your asphalt roof, ask how the process will protect the shingles and whether the manufacturer specifically approves that method.
How to Prevent Roof Algae and Moss
Cleaning is only one part of asphalt shingle maintenance. Preventing the conditions that encourage algae and moss can reduce the amount of buildup your roof experiences.
Keep Tree Branches Trimmed
Overhanging branches can shade the roof and prevent moisture from drying quickly. They can also drop leaves, twigs, and other debris onto the shingles.
Trimming branches away from the roof can allow more sunlight and airflow while reducing the amount of organic material that accumulates.
ARMA similarly recommends keeping tree branches trimmed to reduce shade and debris that can encourage moss and algae growth.
Keep Gutters Clean
Gutters are an important part of your home’s drainage system. When they become clogged, water may not drain properly.
Keeping gutters clear helps direct water away from the roof and foundation.
This is particularly important when you’re trying to prevent excess moisture from contributing to roof algae or moss growth.
Remove Roof Debris
Leaves and other organic debris can trap moisture against asphalt shingles.
If debris accumulates on the roof, it should be removed using a non-abrasive method. ARMA recommends a leaf blower or similar approach rather than brushing or scraping.
Address Moss Early
A small amount of moss can become more difficult to manage as it spreads.
If you notice moss developing, consider having the roof evaluated rather than waiting until the growth becomes widespread. Moss can interfere with water shedding and may contribute to shingle damage when left unchecked.
When Should You Hire a Professional for Asphalt Roof Cleaning?
Roof cleaning may appear to be a simple home maintenance task, but working on a roof presents serious safety risks.
A professional is especially recommended when:
- The roof is steep.
- The roof is wet or slippery.
- There is widespread moss or algae.
- Shingles appear damaged.
- You aren’t sure which cleaning solution to use.
- The roof is difficult to access.
- You suspect the roof is nearing the end of its service life.
- You want the roof inspected while it is being cleaned.
ARMA specifically warns homeowners about the hazards involved with walking, climbing, or working on asphalt roofs and recommends that trained professionals handle this work.
Does Cleaning Asphalt Shingles Extend Roof Life?
Cleaning can improve the appearance of a roof and help address biological growth, but it should not be considered a way to reverse normal roof aging.
Algae discoloration is primarily an aesthetic concern, while moss can create more serious problems for asphalt shingles.
If a roof is already showing signs of deterioration, cleaning it won’t restore damaged shingles.
Watch for signs such as:
- Curling shingles
- Cracked shingles
- Missing shingles
- Excessive granule loss
- Damaged flashing
- Sagging
- Water stains
- Persistent leaks
If you’re seeing these problems, you may need repairs or roof replacement rather than simply cleaning the roof.
For example, granules collecting in gutters can be a sign that asphalt shingles are deteriorating. Bak Brothers’ guide to roof replacement costs in Chicago discusses several signs homeowners should consider when determining whether a roof may be approaching replacement.
Professional Asphalt Roof Cleaning vs. DIY Cleaning
The biggest benefit of professional roof cleaning isn’t simply removing stains. It is having someone who understands how to approach the roofing system without unnecessarily damaging it.
A professional can:
- Identify algae, moss, and other growth
- Look for damaged shingles
- Recommend an appropriate cleaning method
- Follow manufacturer guidance
- Use appropriate safety equipment
- Protect surrounding property
- Identify potential roofing problems
- Determine whether cleaning is appropriate
If cleaning reveals significant roof deterioration, a professional can also help you understand whether repair or replacement is the better long-term option.
Keep Your Asphalt Shingles Clean and Your Roof Protected
Knowing how to clean asphalt shingles can help you understand what causes roof discoloration, how algae and moss affect your roofing system, and why aggressive cleaning methods can cause more harm than good. Gentle, manufacturer-approved cleaning methods are preferable to pressure washing or abrasive scrubbing, while regular asphalt shingle maintenance can help reduce the conditions that encourage biological growth.
If your roof has heavy algae or moss, visible damage, or other signs of aging, don’t risk your safety trying to clean it yourself. Call Bak Brothers, Inc. at 224-332-2778 or request a free quote to discuss your roofing needs and find the right solution for your home.
FAQ About How to Clean Asphalt Shingles
Can I Pressure Wash Asphalt Shingles?
No. Pressure washing is not recommended for asphalt shingles because high-pressure water can remove protective granules and damage the roofing system. ARMA specifically states that power washers should not be used on asphalt roofing.
What Is the Best Way to Clean Asphalt Shingles?
The appropriate method depends on the shingle manufacturer and the type of growth present. Generally, clean asphalt shingles using a manufacturer-approved cleaning solution and gentle application rather than aggressive scrubbing or pressure washing.
How Do I Remove Black Streaks From Asphalt Shingles?
Black streaks are often caused by algae. A properly selected and diluted cleaning solution can lighten the discoloration, but the cleaning process should be performed carefully to avoid damaging the shingles. ARMA notes that algae discoloration can return after cleaning.
Is Moss Bad for Asphalt Shingles?
Moss can be more problematic than algae. Established moss can lift or curl shingle edges, hold moisture against the roof, and interfere with proper water shedding.
How Often Should Asphalt Shingles Be Cleaned?
There isn’t one universal cleaning schedule for every asphalt roof. The need depends on the roof’s exposure to shade, moisture, trees, debris, algae, and moss.
Instead of cleaning on a strict schedule, inspect the roof regularly and address problems when they appear.
Should I Clean My Roof Myself?
Some homeowners can handle ground-level maintenance, such as trimming nearby branches and keeping gutters clear. However, climbing onto a roof for cleaning can be dangerous.
If your roof is steep, wet, slippery, damaged, or difficult to access, professional service is the safer option.
