Best Chemicals for Roof Cleaning: A Professional's Guide

Roof cleaning is one of the most profitable services a pressure washer can offer. But it requires the right chemicals mixed at the right strength. Get it wrong and you could damage the roof, kill landscaping, or create a liability nightmare. This guide covers everything you need to know.

Safety First

Roof cleaning chemicals are dangerous. Always wear proper PPE including chemical resistant gloves, eye protection, and a respirator. Never mix bleach with other chemicals (especially acids) as this can create toxic gases.

The Primary Chemical: Sodium Hypochlorite (SH)

Sodium hypochlorite, commonly known as bleach, is the foundation of almost every roof cleaning solution. It kills the algae (Gloeocapsa magma), moss, lichen, and mold that cause those ugly black streaks on roofs.

Understanding SH Strength

Sodium hypochlorite comes in different concentrations. The strength matters because it determines your final mix ratio.

Pool chlorine: Usually 10% to 12.5% SH
Industrial SH: 12.5% is the most common
Household bleach: Only 5% to 6% (not strong enough)

Pro Tip

SH degrades over time, especially in heat. Fresh SH from a pool supply store is stronger than SH that has been sitting in a hot warehouse for months. Test your SH strength regularly.

Recommended Mix Ratios for Roof Cleaning

Your final mix strength (what actually hits the roof) should typically be between 3% and 6% SH depending on the level of growth and roof type.

Condition	Target Mix	When to Use
Light staining	3% SH	Minor algae, maintenance wash
Moderate growth	4% to 5% SH	Typical roof with black streaks
Heavy growth	5% to 6% SH	Thick algae, moss, or lichen
Maximum strength	6% SH max	Only for extreme cases, test first

Calculating Your Mix

If you are using 12.5% SH and want a 4% final mix, you need to dilute it. The formula is:

(Target % / Starting %) x 100 = Percentage of tank that should be SH

(4 / 12.5) x 100 = 32%

So for a 100 gallon tank: 32 gallons SH + 68 gallons water

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Essential Additives

1. Surfactant

A surfactant (soap) is essential for roof cleaning. It helps the solution stick to the roof surface and dwell longer, allowing the SH to work.

Recommended amount: 4 to 8 ounces per gallon of mix
Popular brands: Elemonator, Simple Cherry, Cling On
Avoid: Dawn dish soap (foams too much and can streak)

2. Scent (Optional)

Many washers add a scent to mask the bleach smell. Cherry and lemon are popular choices. This is more about customer perception than cleaning power.

Protecting Landscaping

SH will damage or kill plants if you are not careful. Follow these steps to protect landscaping:

Pre-wet all vegetation: Saturate plants, grass, and shrubs with water before you start
Cover sensitive plants: Use plastic tarps for delicate plants
Rinse during the job: Have a helper spray water on plants while you work
Rinse again after: Thoroughly rinse all vegetation when finished
Use neutralizer (optional): Some washers spray a neutralizer like Rinse Aid

Never Use These on Roofs

Pressure: Never pressure wash asphalt shingles
Acids: No muriatic acid, phosphoric acid, or similar
Mixing chemicals: Never mix bleach with other products
Hot mix: Do not apply to roofs in direct sunlight over 90F

Application Method

For roof cleaning, you will typically apply your soft wash solution using one of these methods:

12V pump system: Most common for residential roofs. Low pressure, high volume.
Air diaphragm pump: Better for larger jobs, can shoot further.
X-Jet or M5 downstream: Uses your pressure washer to apply at low pressure.

Step by Step Roof Cleaning Process

Inspect the roof: Walk around and look for damage, missing shingles, or problem areas
Pre-wet landscaping: Soak all plants with water
Mix your solution: Calculate the right ratio for the job
Apply solution: Start at the bottom, work up. Overlap your spray pattern.
Let it dwell: Allow 15 to 20 minutes for the chemicals to work
Rinse (if needed): Some washers rinse, others let rain do it
Rinse plants: Thoroughly rinse all vegetation
Document your work: Take before and after photos

Frequently Asked Questions

Do I need to rinse the roof?

Not always. Many professional roof cleaners apply and leave, letting rain rinse the roof over time. The results continue to improve for days or weeks. However, rinsing can give instant results that look better for before and after photos.

How long should I let the solution dwell?

Typically 15 to 20 minutes. You will see the organic growth start to change color as the SH kills it. In hot weather, do not let it dry on the roof.

Can I clean a roof in direct sunlight?

Ideally, no. SH is less effective on hot surfaces and evaporates faster. Try to clean roofs in the morning or on overcast days. If you must clean in sun, wet the roof first and work quickly.

Conclusion

Roof cleaning is a high profit service when done correctly. The key is using the right chemicals at the right strength, protecting landscaping, and following proper safety procedures.

Start with a 4% mix on moderately dirty roofs and adjust based on results. Always err on the side of caution. It is easier to make a second pass than to explain why you damaged someone's roof or killed their landscaping.