How to SAFELY Pressure Wash a Metal Roof

Metal is the second most common choice of roofing materials, with asphalt shingles being the most common. It is estimated that 750,000 U.S. homeowners have a metal roof as of 2015. But how do the people who own houses with metal roofs clean them safely?

You can pressure wash a metal roof as long as you use a lower amount of pressure and a wider nozzle tip. If you use too much pressure, you will damage the metal roof over time, even if it is not noticeable at first glance.

If you do choose to pressure wash your metal roof or clean it with other methods, there are many factors that you need to consider.


Your safety is the most important thing to consider when cleaning any roof, especially a metal one, as it can become very slippery when wet. If you have a metal roof that has a very steep slope, do not try to climb on top of it to clean it. You will most definitely fall and become seriously injured since there are very few places that you can get your footing when the roof has a steep slope.

If your metal roof does not have a steep slope, then you can go on top of it to clean it. However, take precautions and be careful while you are on top of the roof. Even after a metal roof has been cleaned, it can be very slippery.

Listed below are some safety tips to consider before climbing on top of a metal roof.

  • Wear a harness and have a fall safe nearby that will catch you if you fall off of the roof.
  • Wear good non-slip shoes. It helps if they are also waterproof, but they do not have to be if you do not have waterproof shoes. This will prevent you from slipping and falling off of the roof.
  • Have someone that you trust standing on the ground below you. They can hold the ladder while you climb down off of the roof, and if you fall off of it they can call emergency services and get medical help for you.
  • Do not drench the entire roof at one time while you are standing on it. Yes, the roof needs to be wet for you to clean it, but there do not need to be rivers of water coming off of your roof while you clean it.
  • Stand on the ridges of the roof, if the metal roof that you are cleaning has ridges, and stand in one place as much as possible. Your hose or pressure washer should be able to reach the entire roof in most cases.

Pressure Washer

Pressure washers are very easy to buy or rent. However, pressure washers are very expensive, even if you buy a used one in good condition. You can rent one if you do not think that you will use a pressure washer often and do not want to make a large investment, but renting a pressure washer can also be expensive.

The average cost of renting a pressure washer from a home center costs $40 to $100 per day, depending on the type of pressure washer and where you rent it from.

If you want to purchase a pressure washer, the prices range from $100 to $600, depending on what type of pressure washer you purchase and where you purchase it from. An electric pressure washer will cost you anything from $100 to $400, and a gas pressure washer will set you back $300 to $600, not including the cost of the gas and water that you will use when you use your pressure washer.

The pressure washer will come with the tips included in most cases, although you should double-check the product description to make sure that they are included before you purchase the pressure washer unit. If the pressure washer does not come with hose tips, they are very easy to find and purchase.

When cleaning a metal roof with a moderate to a high pitch, do not climb on top of it. This is very dangerous, and it is nearly impossible for you to find a place where you can get a good foothold. Listed below are instructions on how you should clean your metal roof if it has a moderate or high pitch. A pitch defines the angle or steepness of a roof.


  1. Spray your roof with water from a long hose or a pressure washer with gentle pressure. You can also use a typical garden hose if your hose and nozzle have enough pressure. Start from the top and work your way to the bottom. The running water will make it easier for you to remove the grime from the bottom part of the roof.
  2. Let a cleaning chemical sit for at least 20 minutes. The longer you let it sit, the better, but do not let it dry completely yet, or else it won’t do its job properly.
  3. Spray your roof with diluted ammonia or bleach or another cleaning chemical. The strength of the mixture will change depending on how dirty your roof is, but it is recommended that you use a 3% mixture. If you want to wash the roof with a simple detergent, then that works too.
  4. Spray the roof with a pressure washer. Use the 40-degree tip because you do not need a lot of pressure to get the grime off of the roof. Spray any especially bad areas until they are clean and you are satisfied, but the majority of the roof should only need a rinse at this point.

When you are cleaning a flat metal roof with slight slopes, feel free to climb on top of it to clean it, but it can become very slippery and can be dangerous to be on top of. When you are standing on a metal roof, stand on the raised ridges to avoid slipping and falling. After you are on top of the roof, perform the same steps that are listed above.

The video below has some tips for mixing chemicals in large amounts and suggestions for the types of chemicals that you should use to clean metal roofs:

How To Prevent Damage To Your Metal Roof

Metal roofs are durable, but they can be easily damaged if you wash them under too much pressure. To avoid damaging your roof with a pressure washer over time, use a 40-degree tip. This is the widest tip, but it will get the job done quickly and efficiently. Also, when it is used on a flat tip, it is very effective and quick to get rid of algae, mildew, mold, and other debris.

Metal roofs can withstand a higher pressure nozzle, but repeated and extended use of the higher pressurized nozzles is not recommended, since they can damage the roof slightly over time, even if it does not seem like there is any immediate damage.

Use a ladder with padded stabilizers. Metal roofs have unique coatings that protect them. If you want to prevent scratching and damaging this coating, then you will want to make sure that your ladder stabilizer arms have a soft surface touching the roof. This will also prevent the ladder from falling while you are not using it, which is always helpful.

When To Clean A Metal Roof

Grime and algae can easily build up on a metal roof, especially if you live in a wet climate. Many people choose to only clean their metal roof once a year, depending on the weather and their preferences, but others choose to do it more frequently. The frequency that you clean your roof is up to you.

If the grime, moss, and algae have begun to bother you or your family members, then it is time to clean it. The grime is not likely to damage the metal, and neither can the algae or the moss. 

Should I Hire Someone to Clean My Roof?

If you do not feel comfortable climbing up on top of your roof to clean it, or you do not feel that you have enough time to clean it, although it needs to be done, then feel free to hire a professional roof cleaner. They have the necessary tools to clean almost any type of roof, and they have safety equipment that may be hard for you to find on your own.

Roof cleaning workers also are typically covered by their company if they get hurt while on the job, while you do not. They also have more experience than you probably do when it comes to cleaning high places.

The cost of having a professional roof cleaner clean your roof varies depending on the company and their rates, but the average cost of a metal roof cleaning is between $0.20 and $0.70 per square foot.

The company that you choose to use to clean your roof may charge other fees for their services, such as a labor fee and deposit, but that cost will vary depending on the company that you choose to hire. Most roof cleaning companies will come to your home and give you a cost estimate for free before you purchase their services, so you can choose what company’s price is best for you and your budget.

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