How to Clean a Metal Roof

metal-roofMetal roofs are incredibly popular for their longevity and durability. Interestingly, there are also extremely popular in wooded and rustic areas due both to the way that the metal roof looks on log cabins and other rustic-style homes, and the way that it performs in these areas. Unfortunately, these types of locations often mean that the roof is going to get dirty, detracting from its overall beauty, and potentially trapping moisture or other harmful debris against the metal where it can begin to corrode. Therefore, it’s important to keep your metal roof clean to ensure that it stays looking and functioning at its best.

What You’ll Find on a Metal Roof

Metal roofs are often subject to the same types of dirt and debris that you’ll find on clay and asphalt roofs. The biggest difference that you’ll find is that metal roofs don’t tend to stain from blue/green algae or grow moss as frequently, otherwise you’ll see the same types of dirt.


In addition to mold, mildew, algae, moss, and dirt, you may also find some small areas of rust or corrosion on the roof as well, depending on how old the metal is, and what type of metal your roof is made of. It’s also not uncommon for painted metal roofs to show more dirt on their surface than unpainted metal roofs, and for painted roofs to be more difficult to clean.

What to Watch Out For

Cleaning any roof can be hazardous, particularly if you plan on climbing up on the roof itself to wash it. Many people mistakenly believe that metal roofs can be simply hosed off, or even power washed. Unfortunately, a simple garden hose is often not enough to free most of the dirt from the roof, while a power washer may dent the metal or cause corroded areas to sustain even worse damage.


Therefore, it’s usually best to clean a metal roof from on top of the house itself. Keep in mind that metal roofs tend to be much more slippery than an asphalt roof, and that many aluminum roofs will also dent easily if walked on.

Before you can clean your metal roof, you’ll need to do a thorough inspection of the roof itself. This is because metal roofs may harbor some areas of corrosion, and this corrosion may weaken the roof, making it more hazardous to walk on. Some standing seam roofs may also have sharp edges, particularly if a seam has bent or moved over time, which can also make cleaning the roof more dangerous. If you find either of these on your roof, you may want to call for a professional roofer to help clean and repair your roof before you attempt to clean it yourself.

In addition to areas of damage, you also want to take a look at what it is that needs to be cleaned from your roof. White roofs that have been stained by blue/green algae may require a different cleaner than a green roof which merely has a few built up layers of dust, debris, and pine sap.

It’s always best to know what it is you’re looking at before you begin cleaning your roof. If at any time you’re unsure of what it is you’re trying to remove, you’re unsure if your cleanser will harm the painted surface of your roof, or you worry about potential corrosion or damage to your roof, call your roofer for an inspection before proceeding.

Cleaning Your Metal Roof

If you’ve inspected your roof and found no damage, and you feel comfortable getting up on your roof itself, you’ll need to determine what it is you’re cleaning from it, so that you can remove it in a timely way. Keep in mind that most roofs take approximately three hours to clean, and that you may want to test some cleansers on an inconspicuous area of your roof to make sure they don’t mark or streak the painted surface before you begin applying them to the entire roof surface.

Removing Algae, Mold, or Mildew

If you need to remove algae, mold, or mildew from your painted roof, you’ll go about doing so in much the same way that you’d remove it from a standard roof; by changing the PH. Living organisms on the roof can only survive at the current PH level; if you raise or lower the PH, the organism will die, allowing you to clean the stain from the roof easily.

Vinegar, bleach, ammonia, and salt will all effectively change the PH level of your roof, allowing you to clean it. Use only one of these substances, mixed with water, at a time: Never mix chemicals together.

Spray the roof with the diluted substance and let it sit for about an hour. Then use a soft-bristled scrub brush to remove the stain from the roof itself and rinse with clean water.

Removing Fungus Stains

Sometimes you may find that there’s a very stubborn stain on your roof that is caused by heavy fungus growth. This type of stain doesn’t usually respond well to gentle spraying and cleaning and requires a heavier hand. Thankfully, what tends to remove it best is a PH neutral dish soap such as Dawn or Ivory, and lots of clean water. You may need to exert some pressure on the bristles of your scrub brush as you work to remove the stain, and you may need to go over each area two or three times to get the roof clean, particularly on lighter colored roofs.

Removing Dirt, Sap, and Other Stains

There are a lot of different substances that can build up on your roof. Pine sap, decaying leaves, and even road dirt that’s drifted into the air can settle on your metal roof and stain it. Most of these substances can be removed by a mixture of ½ cup tri-sodium phosphate and 1 gallon of water. Spray this mixture onto the roof, and agitate it with a soft-bristled brush to get it clean.

To avoid streaks, start cleaning at the bottom edge of the roof and work your way up, rinsing frequently with lots of fresh water. Remember to test this solution on an out of the way area to ensure that it won’t harm your roof’s finish.

Keep Your Roof Clean

A dirty roof can detract from your home’s curb appeal and resale value, while potentially harboring water and other corroding materials that can cause your metal roof to rust. Make sure your keep your roof clean to help your entire property look and function at its best.


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2 thoughts on “How to Clean a Metal Roof

  1. Thank you for talking about what to watch out for when cleaning a metal roof! I will just get a professional to come do it for me so I don’t mess anything up. These tips were really helpful! Thanks again!

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