What is the ARMA approved method for cleaning roof algae?

The Asphalt Roofing Manufacturers Association (ARMA) recommends soft washing as the only approved method for cleaning algae from asphalt shingle roofs. This method uses a low-pressure application of a biodegradable cleaning solution, typically containing sodium hypochlorite (liquid chlorine), applied at low pressure to kill algae without damaging shingles.

Why does ARMA prohibit pressure washing roofs?

ARMA prohibits pressure washing because the high-pressure water stream (often thousands of PSI) strips away the protective ceramic granules embedded in the shingle surface. These granules protect the asphalt from UV degradation. Once removed, they cannot be replaced, and the shingle begins to deteriorate rapidly. Pressure washing can also void the manufacturer warranty.

What chemicals are used in soft washing a roof?

Professional soft washing uses a solution primarily based on sodium hypochlorite (liquid chlorine), combined with surfactants that help the solution adhere to the roof surface and penetrate the algae colony. The solution is biodegradable and is applied at very low pressure, similar to a garden hose, so it does not damage the shingles.

What ARMA Says About Cleaning Algae From Shingles

Understanding the ARMA Position on Roof Cleaning

The Asphalt Roofing Manufacturers Association (ARMA) is the trade body representing the companies that design, engineer, and warranty the shingles on your roof. When ARMA publishes a guideline, it typically represents the collective position of every major roofing manufacturer in North America.

Their position on roof cleaning is unambiguous: soft washing is the only approved method. Pressure washing is explicitly prohibited.

What Exactly is Soft Washing?

Soft washing is a cleaning process that relies on chemical action, not mechanical force, to remove biological growth from a roof. The process is done using specialized equipment to apply a biodegradable cleaning solution designed to eliminate algae, moss, and related growth, without damaging the shingles.

The Key Components

Low Pressure Application: The cleaning solution is applied at pressures comparable to a standard garden hose. This is dramatically different from pressure washing, which operates at pressures many times higher.
Sodium Hypochlorite (Liquid Chlorine): The primary active ingredient that kills Gloeocapsa magma and other biological growth on contact. This is not household bleach. Professional-grade liquid chlorine is formulated specifically for exterior cleaning applications.
Surfactants: Chemical additives that help the cleaning solution adhere to the shingle surface and penetrate the algae colony rather than running off immediately.
Dwell Time: The solution is allowed to sit on the roof surface for a controlled period, giving it time to fully eliminate the algae colony at its root system.
Low-Pressure Rinse: After adequate dwell time, the solution is gently rinsed using low pressure water.

Why Pressure Washing is Prohibited

ARMA does not simply "recommend against" pressure washing. They explicitly prohibit it. Understanding why requires understanding how asphalt shingles are constructed.

Every asphalt shingle has a layer of ceramic-coated granules embedded into its surface. These granules serve two critical functions:

UV Protection: The granules shield the asphalt layer beneath from ultraviolet radiation. Without them, the asphalt oxidizes and degrades rapidly.
Weather Resistance: The granules provide the first line of defense against rain, hail, and wind-driven debris.

When a pressure washer hits an asphalt shingle at high pressure, it blasts these granules off the surface. You can literally see them washing into the gutters as dark, sandy sediment. Once these granules are removed, they cannot be put back. The exposed asphalt begins deteriorating immediately.

Warranty Implications

Pressure washing your roof can void the manufacturer warranty on your shingles. If a warranty claim is denied because of evidence of pressure washing damage, the homeowner has no recourse. This applies to all major roofing manufacturers.

The Professional Soft Wash Process Step by Step

A properly executed professional soft wash follows a consistent process:

Pre-inspection: Assess the roof condition, identify areas of heavy growth, check for pre-existing damage.
Plant and landscape protection: Cover sensitive plants and wet down landscaping around the foundation.
Solution mixing: Prepare the cleaning solution at the appropriate concentration for the severity of growth present.
Low-pressure application: Apply the solution starting from the bottom of the roof working upward to ensure complete coverage.
Dwell time: Allow the solution to work for the appropriate duration based on growth severity.
Low-pressure rinse: Gently rinse the roof surface, again working from bottom to top.
Landscape rinse: Thoroughly rinse all surrounding vegetation and surfaces.
Post-inspection: Verify complete treatment and document with before and after photos.

How to Identify a Qualified Professional

Not all companies advertising "roof cleaning" use the correct methods. Here are the key questions to ask:

Do you use the ARMA-approved soft wash method exclusively?
What PSI does your equipment operate at?
Do you use sodium hypochlorite (liquid chlorine) based solutions?
Will you provide before and after documentation?
Do you carry liability insurance and workers compensation?

If a company mentions "pressure washing" or cannot clearly explain the soft wash process, move on. In Metro Atlanta, companies like Blue Mountain Exteriors specialize in ARMA-approved soft wash roof cleaning.

The Bottom Line

ARMA exists to protect the integrity of asphalt roofing systems. Their approval of soft washing and prohibition of pressure washing is not arbitrary. It is based on engineering data and decades of field experience. When choosing a roof cleaning method, following the manufacturer guidelines protects your shingles, preserves your warranty, and ensures the longest possible roof life. Learn more about your cleaning options here.