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Metal Roof Cleaning: A Complete Guide by Ryan Cash and Rooftec Systems

Ryan Cash

UAMCC Associate Member
How do you clean a metal roof?
Can you use SH on a Galvalume Roof?
How do you clean a home with Copper Gutters?

Whenever you approach a metal roof, the first thing you need to do is properly identify what type of material it is.

The main types of metal you will encounter on a home are Galvanized Steel, Galvalume, Aluminum, and Copper

Galvanized Steel
is a type of steel roofing that has been around for hundreds of years. The process of galvanizing involves hot-dipping the steel sheeting in a protective zinc coating. Before the introduction of Galvalume, using galvanized steel was common practice. So this type of metal will typically appear on older homes. Galvanized roof typically doesn’t have a product warranty.

One of the main places you’ll still find Galvanized Steel is for use on structures that house animals (Farmland, etc.) the manure from animals breaks down other types of metal roofs (Galvalume) and reacts to the it’s coating. Because of this, Galvanized steel is usually still used for these applications.

roofing combines three of the most important metals used in roofing- Steel, Aluminum, and Zinc. A Carbon steel sheet is hot-dipped in aluminum and zine allows until it has a proper coating. The process is now the most popular type of metal roofing because it allows the roofing material to have the positive characteristics of each individual metal. It is typically more corrosion resistant than Galvanized steel.

Galvalume roofing manufactuers recommend not using this type of roofing material near the ocean because the salt in the air (Sodium chloride) prematurely degrades the material.

Very few metal roofs are galvanized in the last 10-15 years . Galvalume is pretty much the standard these days. When cleaning, you actually need to pay very close attention to the hardware (screws, etc.). Roofs with galvanized or painted hardware can be a liability as the screw heads and seals can rust and deteriorate with cleaning.

Aluminum Roofing comes with a painted finish and typically have their own warranties. The biggest difference is that aluminum will oxidize (chalk) as it’s exposed to sunlight and weather. Aluminum, however, will not look unsightly and continue on with a rapid deterioration/rust like steel will. Aluminum is also very resistant to salt water corrosion so it will often be found in coastal regions.

Copper Roofing is extremely long lasting, but is very soft and can easily be dented/damaged. However, this damage from falling branches/hail stones/etc. may only be aesthetic in nature, where harder metals may puncture and lead to leaks. Copper roofs are extremely expensive but also have a tendency to expand and contract with fluctuations in temperature.


There are a few ways to tell the difference between the type of metal a roof is constructed out of.

  • The first being a magnet test.
    • A magnet will stick to galvalume and Galvanized steel roofs (as they has a steel core).
    • Aluminum and Copper roofs are non-magnetic

  • The second big difference is the look.
    • Galvalume typically has a smoother, matte appearance, while galvanized coating is more rough and shiny.
    • Copper roofs are pretty easily distinguished by their color (If you cant tell, you can always scratch a small spot in an inconspicuous area.

So, now that you’ve determined what type of roof it is, how do you clean it?

The first, and one of the most important things to consider when cleaning a metal roof is the temperature.

Avoid cleaning metal roofs in the middle (heat) of the day. If the roof is in direct sunlight, cool it down first with water. You absolutely do not want SH to dry on a metal roof. Go slow, cleaning one section at a time.

Second, check the hardware on the roof. Check first to see if the fasteners are galvanized or painted. Most roofs should have quality hardware but if you can scratch it with wire brush and remove color, then the fasteners may rust after cleaning, regardless of how much rinsing you do.

If a roof is Galvanized Steel, Galvalume, or Aluminum you CAN use SH to clean it. But you’ve got to be careful. Bear in mind that every roof is different and may require different methods, but here’s the basic process.

  1. Perform a Test spot in an innocuous spot (if roof becomes discolored, walk away from the job)
    1. Let the customer know you'll be performing a test spot and that you will walk if it fails
    2. Test small area with 2-3% SH
    3. Dwell (5-10 minutes), DO NOT allow roof to dry
    4. Rinse
    5. Wait 5-10 minutes
    6. If roof hasn’t discolored, move forward with cleaning
  2. Have customer sign waiver, stating that they take responsibility for any discoloring of roof caused by the process
    1. If they refuse the waiver, or the roof fails your spot test, offer an alternative or walk away
      1. Temper expectations
      2. Use a product like Simple Green and brush every area of the roof
      3. Charge according to your time and work (Price will be much, much higher)
  3. Remove loose debris with a blower/soft brush (Car wash brush)
    1. Be careful not to scratch roof and remove any of the protective coating on the metal
    2. Sometimes, a good soaking with a large orifice spray tip is enough to rinse debris down
  4. Pre-wet Roof with Water and cool it down
  5. Continue soaking roof until it is cool/cold to the touch
  6. You do NOT want SH to have a chance to dry on the roof
  7. Start with a very light mix (0.5%) and work up to a max of about 1-2% if needed.
    1. 1% is generally the max needed
    2. 2% may be used on some commercial roofs
  8. Allow to dwell for a couple minutes before rinsing (5-10 minutes max)
  9. Rinse
  10. Rinse
  11. Rinse (a lot)
  12. If you want to be extra thorough, treat roof with a bleach neutralizer when finished rising to help mitigate any risk of flash-oxidizing the metal roof
  13. If the roof is painted and is oxidized, consider talking to the customer about adding on oxidation removal (restoration)

For proper Cleaning of a Copper roof, the first thing you have to remember is that more than likely, the customer does not want you to remove the natural patina/tarnish that comes with the age of the roof. They also likely don’t want you to discolor and darken the roof either. Likely they are wanting organic growth or debris removed from their home.

Actual copper roofs are very uncommon, however, copper gutters and awnings are routinely found around the United States. In either case, MOST contractors will choose to walk away from these jobs as the potential risk of discoloring and ruining the patina is very high.

Sodium Hypochlorite and surfactants with high pH values should not be used on or around copper.

If a home has copper gutters, it’s actually best to mask off the gutters and cover them before even performing siding cleaning/house wash.

Any process that will remove mold stains and algae stains will affect the patina on the copper gutters.

So what’s the process for cleaning copper?

  1. Consider walking away from the job
  2. Consider masking off/covering all copper before cleaning
  3. Remember you are attempting to clean the copper (not restore it)
  4. Pre-soak with water
  5. Apply a very light mix of a neutral pH detergent or soap
    1. Car Wash Soap
    2. Dawn Dish soap
  6. Brush with a very soft brush (car wash brush)
  7. Use enough elbow-grease to remove debris
    1. Be careful not to disturb natural patina/oxidation
    2. This Is a very time consuming/delicate process
  8. Rinse very well.
  9. Charge Accordingly

As with any job you take on, spending extra time in the beginning doing research will pay off on the back end of the work. Make sure to speak to the customer about their expectations, the type of material the roof is made from, and possibly what brand roof it is If they know.

Knowing the manufacturer gives you the ability to research and follow their specific cleaning guidelines. IF THE MANUFACTURER SAYS NOT TO USE BLEACH/SH ON THEIR MATERIAL, DON'T DO IT!

If you don't feel comfortable or are worried about the job, don't hesitate to walk away! It's ok to turn down jobs!
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