Roof Cleaning 101: ARMA Guidelines and Best Practices
Master the fundamentals of safe roof cleaning. Learn ARMA guidelines, types of roof contamination, chemical selection by material, safety protocols, and pricing strategies for professional contractors.
The ARMA Standard: No Pressure Washing
The Asphalt Roofing Manufacturers Association (ARMA) has established clear guidelines for roof cleaning that every professional contractor must understand. The core principle is absolute: No pressure washing of asphalt shingle roofs under any circumstances.
This isn’t a suggestion or a preference—it’s an industry standard backed by decades of durability data. Pressure washing damages shingle integrity in ways that are often not immediately visible but lead to accelerated failure, water infiltration, and voided warranties.
The Asphalt Roofing Manufacturers Association explicitly prohibits pressure washing asphalt shingles. The only approved method for roof cleaning is soft wash application with approved chemical solutions and low-pressure rinse.
Types of Roof Contamination
Understanding what you’re removing helps you select the right cleaning method and chemical.
Organic Growth (Algae and Moss)
Gloeocapsa magma algae produces those distinctive black streaks. It thrives in damp, shaded conditions and feeds on limestone fillers. Moss is less common on asphalt shingles in most US climates but appears more frequently in Pacific Northwest and similar humid regions.
Algae and moss require soft wash with appropriate biocides (bleach-based or zinc/copper-based solutions). They don’t respond well to pressure alone and will regrow if only physically removed.
Mineral Deposits and Dirt
Dust, pollen, and mineral runoff from metallic flashing accumulate on shingle surfaces. These don’t require chemical treatment and respond well to low-pressure rinsing alone, though a gentle soft wash may accelerate the process.
Lichen and Fungal Growth
Lichen is a symbiotic organism combining algae and fungus. It appears as crusty patches and is more stubborn than algae alone. Fungal growth typically requires longer dwell times with appropriate fungicides.
Granule Loss and Aging
Oxidized or weathered shingles may appear discolored without actual contamination. This is a cosmetic issue and typically not worth treating—it indicates the roof’s age and eventual replacement needs.
Don't assume all dark roofs are algae-covered. Inspect closely to distinguish between:
- Black algae streaks (clearly linear, increase in humid/shaded areas)
- General discoloration from mineral deposits
- Weathering and oxidation (uniform color change)
- Lichen (crusty patches with irregular edges)
Wrong diagnosis leads to ineffective treatment and wasted chemical.
Chemical Selection by Roof Material
Asphalt Shingles
Recommended: Sodium hypochlorite (bleach) at 12-15% SH concentration, diluted appropriately. Alternatives include zinc sulfate or copper sulfate solutions. Avoid highly acidic cleaners as they can corrode flashing and accelerate shingle deterioration.
Wood Shake and Shingle Roofs
Recommended: Softer oxidizing biocides rather than bleach. Bleach can over-lighten wood and damage cedar shakes. Zinc sulfate or specialty wood roof cleaners are preferable. Always test on an inconspicuous area first.
Metal Roofs
Recommended: Mild detergent with low-concentration bleach or copper-based solutions. Avoid acidic products that can pit metal surfaces. Rinse thoroughly to prevent corrosion.
Tile Roofs
Recommended: Bleach-based solutions work well on clay tile. Pressure must stay extremely low (400-600 PSI maximum) to avoid dislodging tiles. Soft wash is ideal.
Slate Roofs
Recommended: Very conservative approach required. Use weakest available biocide solution and minimal dwell time. Slate is brittle and can break under pressure or if saturated too heavily. Consider professional specialty contractors for slate.
Always check the roof manufacturer's care instructions before selecting chemicals. Some manufacturer warranties explicitly restrict certain cleaning products. Using unapproved chemicals can void coverage regardless of application method.
Safety and Fall Protection
Roof work presents serious hazards. OSHA regulations require fall protection for any work at heights over 6 feet.
Minimum Safety Requirements
- Personal fall arrest system (PFAS) with proper harness and rated anchor points
- Hard hat (required in all cases)
- Non-slip boots with proper grip (avoid smooth-soled footwear)
- Eye protection (chemical splash hazard)
- Respiratory protection appropriate to chemicals used (P100 cartridges for bleach vapor)
- First aid kit accessible on-site
Site Setup
- Secure all loose materials that could fall
- Keep equipment cords and hoses clear of walkways
- Use rope and pulley systems for equipment, never carry supplies while securing yourself
- Have someone on the ground as a spotter
- Ensure weather conditions are safe (no high wind, rain imminent, or icy conditions)
Roof work kills and injures. Never cut corners on fall protection. Use rated anchor points, secure harnesses properly, and never rely on gravity alone. A fall from even one story can cause serious injury or death.
The Soft Wash Application Process
Pre-Inspection
Walk the entire roof before starting work. Look for:
- Areas of damage, missing shingles, or compromised flashing
- Roof penetrations (vents, chimneys) that need masking
- Overhanging vegetation that might need trimming
- Gutters and downspouts that need attention
- Roof pitch (steep roofs are more hazardous)
Pre-Rinse (Optional)
A light pre-rinse with low-pressure water (under 600 PSI) removes loose debris and helps ensure even chemical penetration. This step is optional but recommended.
Chemical Application
Apply soft wash solution using a pump-driven sprayer or downstream injection system. Work in sections, maintaining even saturation. Never oversaturate—the solution should be absorbed into the roof material, not pooling on the surface.
Typical application rate is 300-500 square feet per minute depending on solution concentration and roof contamination level.
Dwell Time
Allow 10-20 minutes (depending on contamination severity) for the chemical to kill organic growth. During this time, avoid heavy foot traffic that can disrupt saturation.
Final Rinse
Use low-pressure water only (500-800 PSI) for final rinse. Work top to bottom to push water toward gutters naturally. Ensure complete chemical removal to prevent residue buildup.
Pricing Roof Cleaning Services
Roof cleaning is priced differently than pressure washing due to safety requirements and chemical costs.
Cost Factors
- Square footage: Standard unit is 100 sq. ft. of roof area
- Contamination level: Heavy algae requires more chemical and longer dwell time
- Roof pitch: Steep roofs require more fall protection equipment and slower work pace
- Access difficulty: Complex roof layouts with multiple levels cost more
- Chemical type: Specialty solutions cost more than standard bleach
- Local market: Urban areas and regions with more frequent roof cleaning typically have higher rates
Typical Pricing
Entry-level contractors charge $0.10–$0.20 per square foot. Established contractors with safety certifications and reputation charge $0.20–$0.40 per square foot. High-end services in competitive markets may exceed $0.40 per square foot.
A typical 2,000 square foot roof might cost $200–$800 for professional cleaning, depending on contamination and local rates.
What NOT to Do
Don't:
- Use pressure above 1,000 PSI on any roof surface
- Use zero-degree nozzles or narrow jets on shingles
- Skip dwell time and rinse immediately
- Oversaturate—saturation is enough, puddles are wasteful
- Work alone without a spotter
- Ignore manufacturer care instructions
- Use acidic or corrosive chemicals without testing first
- Apply chemicals during rain or heavy wind
- Skip fall protection on any elevated roof
When Results Take Time
Soft wash kills organic growth but doesn’t instantly remove it. Algae takes 2-4 weeks to fully decompose and wash away. Customers sometimes expect visible improvement within hours—manage expectations clearly in your proposal and follow-up communication.
Results typically reach 60-70% visible improvement within one month and 85-95% improvement within 3-6 months.
Building Your Roof Cleaning Business
If you’re starting a roof cleaning service, focus on:
- Safety certifications: OSHA certifications and CPR/first aid training build credibility
- Insurance: General liability plus tools and equipment coverage (roof work is higher-risk)
- Equipment investment: Soft wash system, PFAS, harnesses, and safety gear require initial capital
- Marketing: Before/after photos (with permission) demonstrate results effectively
- Reputation: Roof cleaning referrals are strong—one satisfied customer leads to multiple neighborhood jobs
Professional roof cleaning, done safely and correctly, is one of the highest-margin services in the pressure washing industry. The key is respecting ARMA guidelines, investing in proper safety equipment, and managing customer expectations about timeline and results.
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