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On average, cleaning a roof will take between two to five hours. This timeline depends on the size and slope of your roof and the severity of any stains. Cleaning roof stains can take additional time, especially if there are signs of moss or algae.

In addition, the age of your roof makes an enormous difference in the time it takes to clean it, as older roofs need more gentle care. If you have significant landscaping in your yard by your house, your professional roof cleaner will need additional time to protect it from cleaning chemicals.

The average cost to clean a roof is around $500, but prices can fall between $150 to $1,000 or more. The size and complexity of your roof are the most significant cost factors, as larger roofs and those with various bump-outs and gables will increase your cost. Your roof material will also make a difference. An asphalt roof will require more labor, as your professional will need to be careful not to damage the shingles. A metal roof can stand up to more intense scrubbing and shouldn’t take as long to clean.

You should avoid using a pressure washer on any surface or item that could be damaged by the high-pressure spray, as some materials are too delicate to withstand the force.

Key items and surfaces to avoid include:

• Electrical Components: Never pressure wash electrical systems, as water can cause short-circuits and create a safety hazard. This includes utility meters, breaker boxes, electrical outlets, generators, and HVAC or air conditioner units.

• Delicate and Fragile Materials: Fragile items can crack, shatter, or be stripped by the pressure. Avoid pressure washing windows, glass, light fixtures, shingled roofs (especially asphalt), and stucco.

• Painted, Stained, or Sealed Surfaces: Unless your goal is to strip the finish, do not pressure wash painted surfaces, stained wood (like decks), or anything with a protective seal that could be stripped away. Be especially cautious with older surfaces that may contain lead paint.

• Soft Woods and Certain Decking: Delicate surfaces like softwood, composite decking, and antique or wooden patio furniture can be etched or damaged. If you must wash wood, use a lower-powered pressure washer with a wide-angle nozzle to prevent damage.

• Living Things: Never use a pressure washer on people, pets, or plants. The force can cause serious injury and will destroy landscaping.

Moss grows in dark areas of roofs, including in corners and gutters. If left alone, it can grow under roofing and cause permanent damage. Here’s how to remove moss from metal roofs: 

• Soak the moss to soften it

• Scrub it away with a soft-bristled brush, or pick it off with your hands (be sure to wear gloves)

• Use a moss remover that’s compatible with metal roofing, following the manufacturer’s directions

• Remove dead moss and rinse the roof thoroughly

• Prevent future moss growth by trimming branches, cleaning gutters, and attaching zinc strips to moss-prone areas