How to Clean a Metal Roof in 8 Steps

Even single-story roofs are high enough for fatal falls, and wet metal roofing is very slippery. Because this project involves ladders, heights, slippery surfaces, and chemicals, plan carefully before beginning and stay alert to possible dangers during the work. Here are some safety precautions you should consider:

• Know what coatings or sealants are on your roof and what cleaning methods are manufacturer approved. Cleaning a metal roof with chemicals or walking on it may invalidate your warranty, so be sure you know what’s allowed.

• Wait for a dry, cool, cloudy, and calm day so you’re working in the best possible conditions.

• Only clean areas you can safely reach.

• Use eye protection and gloves when working with chemicals.

• Only use an OSHA-approved ladder, and consider using a harness or other fall protection.

• Wear shoes that offer good traction.

• Read the use instructions for all chemicals and equipment, and be sure you understand and follow all recommendations.

• Cover landscaping with a tarp or plastic sheeting to prevent damage.

Never get up on your roof alone; always have at least one other person actively assisting you. This person should be willing and able to help you safely climb the ladder, assist you with chemicals and equipment, and monitor the safety situation from the ground. They should know the plan and be able to assist if something goes wrong or call for help in case of an emergency.

Start by walking and talking through the plan. This includes walking through the entire job from start to finish and double-checking that you have all the needed equipment and materials ready. This is also your chance to perform a safety assessment of the roof. Decide where you’ll walk and stand and look for potential hazards and parts of the roof that you need to avoid. Ensure your helper knows their role and what you’ll rely on them to do.

Remove sticks, leaves, and other loose materials before using water or chemicals. Use your hands, a leaf blower, or other tools to free debris from the gutters and roof.

Wet metal roofing is slippery and dangerous. Therefore, it’s absolutely critical that you never walk on wet areas of the roof. Plan to stand on a dry, higher vantage point and spray water away from you and down the roof to clean away dust, debris, and dirt.

Always spray from the top down. Spraying up from the ground can push dirt and debris higher up on the roof and make a bigger mess. Most DIYers use a garden hose and plain water for this task, but if your roof is very dirty and you have experience with this project, you may choose to use cleansers or chemicals. Take your time during this phase, as it’s the main portion of the job.

Note: As tempting as it may be, don’t use pressure sprayers on metal roofing. High pressure can dent and damage metal roofs, and it can remove specialty coatings. Pressure washers are also very heavy and hard to maneuver, and they can cause scratches and dents. Instead, try a gentle-but-effective mixture of ¼ c dish soap, laundry detergent, or car-wash soap per 1 gallon of water.

Once you’ve gone over the roof once, let it completely dry. This will allow you to see the remaining dirt and make it safer for you to move on the dry roof. Locate and have your on-the-ground spotter make a note of areas that need spot cleaning. Then, individually address each remaining dirty area using a sponge, microfiber cloth, soft-bristled brush, or another gentle tool. 

You may need to let areas soak under wet cloths or use approved chemical detergents to soften hard-to-remove dirt. Never use harsh scrubbers like sandpaper, metal brushes, or steel wool, even on stuck-on dirt. These can permanently damage your roof. Then give the roof one final rinse with clean water to completely remove any soap or remaining dirt.

Once you and your spotter agree that the roof is clean, it’s time to get your feet safely back on land. Hand down any equipment and remove hoses, sponges, and other materials from the roof and gutters. Then, ask your friend or spotter to steady the ladder while you carefully climb back down.