Metal roofing has become an increasingly popular choice for both residential and commercial properties across Georgia. A well-installed metal roof can last 40–70 years — potentially the last roof a property owner will ever need to install. But that longevity is contingent on proper maintenance, and cleaning is the foundation of that maintenance program. A metal roof that is regularly cleaned and properly treated can exceed its projected lifespan. One that is neglected, or cleaned with the wrong methods, can suffer premature coating failure and corrosion that requires costly remediation years ahead of schedule.
This guide covers the two primary metal roofing systems used in Georgia, the biological growth threats they face, the correct cleaning approach for each, and the coating protection considerations that make metal roof cleaning distinctly different from cleaning other roofing types.
Standing Seam vs. Corrugated Metal Roofing
The two dominant metal roofing types on Georgia properties have different profiles, installation methods, and, importantly, different cleaning considerations.
Standing Seam Metal Roofing
Standing seam is the premium residential and commercial metal roofing system, characterized by vertical panels that lock together at raised seams running from ridge to eave. There are no exposed fasteners — all connections are concealed within the seams. Standing seam panels are typically steel or aluminum with factory-applied paint finishes (Kynar 500/PVDF coatings are the premium standard) that provide 30–40 years of UV and corrosion protection when properly maintained.
The raised seams create channels where water flows cleanly to the eaves, but they also create shadowed areas that dry more slowly than the flat panel faces. These shaded seam channels are where algae and lichen establish first. The smooth panel faces are generally self-cleaning in heavy rain, but debris and biological growth accumulate in the seam shadows and at the low point of each panel at the eave.
Corrugated and Exposed-Fastener Metal Roofing
Corrugated metal (and related profiles like R-panel and 5V crimp) uses overlapping panels secured with exposed fasteners through the panel face. This system is extremely common on commercial buildings, agricultural structures, barns, and lower-cost residential applications. Exposed-fastener systems are also widely used for metal roofing over porches, carports, and additions.
The corrugated profile creates dozens of horizontal ridges and valleys running across the roof face. These valleys trap debris, moisture, and organic material more aggressively than standing seam panels. Every exposed fastener location is also a potential corrosion point if the neoprene washer under the screw head degrades. Cleaning exposed-fastener roofs requires careful attention to fastener condition, and overly aggressive cleaning (particularly abrasives or high-pressure impact at fastener locations) can accelerate washer degradation.
What Grows on Metal Roofs in Georgia
Metal's non-porous surface might seem inhospitable to biological growth, but Georgia's climate ensures that algae, lichen, and moss find a way. Understanding what's growing tells you what you're treating.
Algae: The Most Common Growth
The same Gloeocapsa magma algae that causes black streaks on asphalt shingle roofs also colonizes metal roofs, particularly on north-facing slopes and in shaded areas. On metal, the algae growth typically presents as a green or dark gray/black film rather than the distinct streaking pattern seen on shingles. The algae produces a pigment that protects it from UV radiation, and this pigment is what creates the visible discoloration. Beyond appearance, algae retains moisture against the metal surface and can begin to compromise the paint film over years of sustained growth.
Lichen: The Serious Long-Term Threat
Lichen is a symbiotic organism — part algae, part fungus — that adheres tenaciously to mineral and coated surfaces. On metal roofs, lichen produces oxalic acid and other organic acids as metabolic byproducts. These acids etch into paint coatings and, at the metal surface if the coating is compromised, accelerate corrosion. Lichen on a metal roof that has been present for several years has literally chemically attacked the paint coating in the areas of contact.
Lichen removal from metal roofing requires chemical treatment first — attempts to mechanically scrape or pressure-blast lichen off metal risk scratching the coating and physically pulling away lichen that has chemically bonded to the coating surface. Even after chemical treatment, lichen "ghosts" (the outlines of dead lichen colonies) may remain for a season before weathering away. This is normal and expected; it does not indicate cleaning failure.
Moss on Metal Roofing
Moss on metal roofing is less common than on shingle or tile roofs but does occur on heavily shaded sections. Moss on metal is primarily a moisture-retention concern — the mat of organic material holds water against the metal surface continuously, which accelerates any existing coating defects. In corrugated systems, moss growing in the valleys can eventually block water drainage at the eave, causing water to back up under the panel overlap.
Why Soft Washing Is the Correct Method for Metal Roofs
The misconception that metal is tough and therefore can handle high-pressure washing is one of the most damaging assumptions in roof cleaning. Metal can handle mechanical force. Metal roof coatings and paint systems cannot.
Paint Coating Protection
The painted finish on a quality metal roof — Kynar, SMP (silicon-modified polyester), or standard polyester — is the primary corrosion barrier for the metal substrate. These coatings are applied at precise film thicknesses in factory conditions. Once a coating is thinned, scratched, or damaged, corrosion begins at that point. High-pressure washing at 2,000+ PSI doesn't visibly abrade metal roof coatings in the way sandpaper would, but it does erode paint film at a microscopic level, particularly at exposed edges, seam surfaces, and anywhere the coating is already thin from UV weathering.
No Abrasives, Ever
Brushes with stiff bristles, baking soda blasting, sand media, or any abrasive material on a metal roof coating is permanently damaging. The scratch pattern from any abrasive creates sites for moisture to undercut the coating, leading to delamination and rust streaking. Even a "soft" brush used with pressure will create fine scratches in the paint film that become corrosion initiation sites. Chemical cleaning — where the solution does the work, not mechanical action — is the only appropriate cleaning mechanism for painted metal roofing.
Soft Wash Chemistry for Metal Roofs
Sodium hypochlorite at 0.5–1.5% is effective for algae and moss on metal roofing. For lichen, which requires more aggressive treatment, some professionals use sodium hydroxide (caustic soda) solutions at controlled concentrations — but these must be applied carefully, as high-pH alkaline solutions can affect some paint formulations and must be thoroughly neutralized and rinsed. The safer standard approach is sodium hypochlorite with extended dwell time (10–15 minutes for lichen treatment) followed by a thorough low-pressure rinse.
Always check with the roof coating manufacturer's recommendations. Some premium roof coatings have specific cleaning restrictions, and using an incompatible chemical can void the coating warranty.
Protecting and Extending Coating Life
Cleaning alone extends metal roof life significantly, but the full maintenance program includes periodic coating inspection and, where appropriate, re-coating before corrosion progresses.
When Coating Starts to Fail
Early coating failure signs include chalking (a white powder on the surface when you wipe it, similar to oxidized car paint), color fade, and small rust spots appearing through the paint. These are signs that the factory coating has UV-degraded to the point where the underlying metal is beginning to be exposed. At this stage, cleaning and applying a metal roof restorative coating can extend the roof's life for another 10–15 years at a fraction of full replacement cost.
Reflective Coating Benefits in Georgia
Metal roofs are inherently more reflective than asphalt shingles, which is one reason they're particularly popular in the South — they reduce cooling loads significantly. Dark algae and biological growth on a metal roof dramatically reduces this reflectivity benefit, increasing summer cooling costs. Regular cleaning restores the reflective performance of the roof coating and provides measurable energy savings for large commercial roofs in particular.
How Often Should Metal Roofs Be Cleaned?
Residential metal roofs in metro Atlanta typically benefit from cleaning every 2–3 years under average tree coverage conditions. Properties with heavy oak or pine tree coverage — particularly those with the roof partially shaded by tree canopy — should plan on annual or biennial cleaning because the organic debris load and shade conditions accelerate biological growth. Commercial metal roofs benefit from annual inspection and cleaning on a preventive maintenance schedule.
The economics are straightforward: regular cleaning at $300–$800 for a residential metal roof (depending on size and pitch) prevents coating damage that would require repainting or restoration at $2,000–$8,000, which in turn prevents full replacement at $15,000–$40,000 for a typical residential metal roof. The return on maintenance investment is among the highest of any property service.
Safety Considerations for Metal Roof Cleaning
Metal roofs are slippery even when dry. When wet with cleaning solution, they are extremely slippery. This is not a roof type that homeowners should walk on while cleaning. Professional crews use fall protection, non-slip equipment, and work from ground-level with extended wands wherever possible. The liability and physical risk of DIY cleaning on a wet metal roof pitch is genuinely dangerous. Our roof cleaning service includes proper fall protection and safety equipment as standard.
We clean metal roofs throughout Atlanta, Marietta, Roswell, Stone Mountain, and the full metro area. Call (678) 748-3578 for a free estimate on your metal roof.