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How to Pressure Wash a Metal Roof Safely: What the Pros Say

Metal roofs are gradually becoming a go-to choice for homeowners and business owners alike, and that too for a good reason. They are well-known for their longevity, tolerance to harsh weather and heat, and low maintenance needs. But if you want to ensure that your metal roof remains in good condition for as many years as possible, you need to give it a seasonal pressure wash.

How to pressure wash a metal roof safely?

Pressure washing a metal roof is safe if you use a lower pressure setting and a relatively broad nozzle tip. Ensure you avoid direct spraying and instead spray at a 40-degree angle with the roof. If you apply too much pressure, you might cause damage to the sheet metal. Always use a detergent mix; if the grime is stubborn, use a bleach solution diluted with water.

There are multiple things to consider before pressure washing your metal roof or cleaning it in any other way. Read the following sections to learn more about the best way to pressure wash a metal roof.

What’s the Best Way to Pressure Wash A Metal Roof?

The best way to wash a metal roof is to spray a cleaning solution from the pressure washer and then rinse it with water. Avoid direct spraying and ensure the spraying angle is kept between 25 to 40 degrees.

However, before you start cleaning, check the type of roof you are dealing with and plan your approach accordingly. For example:

1. Slightly Inclined Flat Metal Roofs

You can walk on this roof but take extreme care because they can become very slick.

2. Moderate to high-pitch Metal Roofs

Instead of climbing onto the roof to clean this metal roof, we advise spraying it with a chemical from the ladder. It may be dangerous to walk on these roofs.


  1. To pressure wash a metal roof, a low-pressure washer at a spray angle of 25 to 40 degrees is recommended. Always use the top-down approach for effective cleaning; running water helps remove grime from the lower sections of the roof easily.
  2. Apply a cleaning solution, i.e., diluted ammonia or bleach, to the roof and let it sit for at least 20 minutes. Keeping the solution dry is essential as this can affect its cleaning abilities. The strength of the mixture depends on the level of grime. The recommended concentration is a 3% mixture.
  3. Rinse the cleaning agent off with a pressure washer with a 40-degree tip.

Note: You can also use simple detergent to clean the roof, depending upon the dirt amount.

How Do You Clean Mold Off A Metal Roof?

To clean mold off a metal roof, apply a cleaning solution and let it settle. Then, use a pressure washer to brush the mold and rinse the solution from the metal roof.

Before cleaning mold off a metal roof, you must wear appropriate safety gear, including:

  • Long Sleeves
  • Pants
  • Gloves
  • Safety Glasses

It is necessary to shield yourself from mold spores and cleaning chemicals. Afterward, follow these steps:

1. Mix A Cleaning Solution: 

Combine equal parts of water and bleach or hydrogen peroxide in a bucket, or consider using commercial cleaning products specifically formulated for removing mold.

2. Apply the Solution: 

Use a garden or pump sprayer to apply the cleaning solution onto areas of the metal roof with mold growth, starting from the top and working your way down. Make sure that all areas with dirt buildup are properly covered.

3. Let it Settle:

Let the cleaning solution set on the moldy areas for 10-15 minutes. This will help it penetrate the mold and loosen it from the metal surface.

4. Gently Scrub the Area:

Use a soft-bristled brush or sponge to scrub the moldy areas gently. Begin at the roof’s highest point and work your way down, applying light pressure to prevent damage to the metal surface.

5. Rinse the Roof:

Thoroughly wash the roof using a garden hose or a pressure washer using the top-down approach. Ensure that all the cleaning solution and mold residue are washed off.

6. Repeat the Process:

If any visible traces of mold remain, repeat the process until the mold is entirely removed. You may need to repeat the cleaning process on heavily soiled roofs multiple times.

Tips to Prevent Future Mold Growth: 

To avoid mold from growing on your metal roof in the future, trim overhanging tree branches to increase sunlight exposure, maintain clean and debris-free gutters, and ensure sufficient ventilation in your attic to prevent moisture buildup.

How Do You Soft Wash A Metal Roof?

Apply low-pressure water when using the soft wash technique on a metal roof to prevent harm or damage. The procedure for soft washing a metal roof is as follows:

1. Use the Right Cleaning Solution:

Mix water with a biodegradable detergent per the manufacturer’s instructions to create a cleaning solution suitable for metal roofs that will not cause any damage to the surface.

2. Apply the Cleaning Solution:

Use a garden or pump sprayer to apply the cleaning solution onto the metal roof surface. Start from the top and move downwards, ensuring all roof parts are evenly covered with the solution. While soft washing, make sure you use the pressure washer in a low-pressure setting to avoid damage to the surface.

3. Wait for the Solution to Absorb & Wash it Off

Let the cleaning solution remain on the surface for about 10 minutes. This will help loosen the accumulated dirt or mold. Afterward, rinse it with cold water thoroughly to remove any residue.

Is It OK to Pressure Wash A Metal Roof?

When cleaning a metal roof, avoid using a high-pressure spray from the pressure washer, as it may cause marks or damage to the sheet metal surface. This pressurized water could also seep under the panel and may cause certain bolts and screws to erode. This eventually reduces the running life of the metal roofing.

Still, pressure washing can be an effective method of cleaning a metal roof if done correctly. Using low pressure and the appropriate nozzle can prevent roof damage, and adding a cleaning solution can dissolve grime and dirt without relying solely on water pressure.

Also, avoid directly spraying at the metal surface and instead spray at a 40-degree angle to lessen the pressure at the surface.

Will Bleach Hurt A Metal Roof?

The excessive use of bleach can harm a metal roof, as it could corrode parts of the metal roof and remove any protective coating. However, when used correctly, diluted bleach can effectively clean mold and mildew from a metal roof.

To ensure no damage occurs, it’s important to dilute the bleach with water to a suitable concentration; the recommended amount is around 10%. This means that 1 part of bleach is diluted with 10 parts of water. Afterward, rinse the roof thoroughly to ensure all bleach has been removed. While using bleach mix, avoid keeping it in direct sunlight or exposing it to freezing temperatures.

Please be aware that if you are allergic to such chemicals or have respiratory issues, avoid using them to wash a metal roof. You can instead switch to some organic cleaners like vinegar or use a detergent solution with water.

Can You Use Vinegar to Clean Metal?

Vinegar is a viable alternative for cleaning metal surfaces. It is a safe, all-natural cleaning solution that helps remove dirt, stains, and grime from metal surfaces.

To clean metal surfaces using vinegar:

  • Combine equal amounts of vinegar and water in a spray bottle.
  • Spray the mixture onto the metal surface and give it time to absorb.
  • Clean the surface with a smooth scrubber or cloth until all dirt and stains are gone.
  • Rinse and thoroughly dry the surface.

Remember that vinegar is an acidic material; therefore, it might not be the best choice for cleaning all kinds of metal surfaces. Acidic substances like vinegar can corrode metals like copper and aluminum. It is best to perform a spot test in an inconspicuous area before using vinegar to clean any metal surface to ensure it is safe for that particular type of metal.

What is the Best Time to Pressure Wash a Metal Roof?

An overcast, dry day with moderate temperature is ideal for cleaning your metal roof. It won’t be slippery. You won’t have to worry about sun reflection limiting your visibility. Finally, and most significantly, a metal roof won’t be scorching hot.

Avoid cleaning your roof on hot, sunny, or wet days. Although it might seem obvious, washing your roof on a wet day is not a good idea. Water increases the likelihood of mishaps and injuries. But you must also not clean your metal roof on a bright, sunshine day.

In direct sunshine, metal roofs heat up to the touch fairly quickly. Not to mention how reflecting they can be. You risk suffering excruciating burns or falling if you decide to clean your metal roof during a bright summer day because your roof’s reflecting ability will make it difficult to see.

What Is the Best Cleaning Technique for A Metal Roof?

To achieve the best cleaning results, make sure you follow these tips below:

  • Use water mainly: Water alone can remove most debris from your metal roof. You can use a hose to remove debris from your roof, such as leaves and twigs.
  • Use detergent to wash dirt: After removing all the hard debris, the top may still have some dirt or mildew. A little detergent, such as dish soap or vehicle washing soap, is required to remove the grime from your metal roof. A gallon of water can be diluted with just 1/4 cup of soap. This mixture is strong enough to remove the dirt from your roof without damaging the protecting layers.
  • Use a soft brush to break the grime: Use a microfiber towel or a brush with incredibly soft bristles to clean the grime.