Project Overview
Working Time: 1.5 hours, depending on extent of moss
Total Time: 2.5 hours
Skill Level: Intermediate
Estimated Cost: $40 to $450, depending on supplies on hand
Before You Begin
Safety
When working on the roof, be sure to use protective gear and a safety rope or harness. Always follow the instructions for safety equipment, and use a securely attached roof anchor bracket that’s appropriate for your roof type.
It’s recommended to spray a roof from the peak down so water can’t work its way under the shingles. If you can’t do this effectively from a ladder, you will need to work on the roof. Call in a pro if you’re not comfortable with heights, or the idea of cleaning the roof yourself.
Wear shoes with traction, and be careful not to damage the roof as you walk on it. (This is of particular concern with metal roofs; even small pebbles or other abrasive materials caught in your shoe tread can scratch metal surfaces.) Finally, grab a friend so you have someone to hold the ladder, hand up supplies, and get help in case of emergency.
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Cleaning Solutions
Research which type of cleaning solution is best for your roof, and avoid types that are too abrasive. “If you’re using the wrong materials or the wrong cleaning solutions,” Prchal cautions, you can cause damage.
DIY Moss Removers: You can mix up your own moss remover, although when you’re wrestling with how to get rid of moss on roof areas, it may be best to stick with products that are specifically formulated \for use on roofs. Go-to cleaners like dish soap and laundry soap may work, but might not be as good for your roof materials or nearby plantings. Some popular DIY moss killers include:
- 8 ounces Dawn Ultra dish soap + 2 gallons of water
- Equal parts liquid chlorine bleach and water
- 1½ to 3½ cups distilled white vinegar and 2 gallons of water
Commercial Moss Removers: There are premixed and mixable roof cleaning solutions available, which makes the process a little quicker. Some popular roof cleaners include:
- Wet & Forget, a spray-on product for removing moss, mold, and mildew stains.
- BioAdvanced Moss and Algae Killer, a spray-on product that relies on potassium soap of fatty acids as its active ingredient.
- Moss B Ware, a zinc sulfate monohydrate powder that can be applied directly to the roof, or mixed with water and sprayed on.
3 Steps to Getting Moss off the Roof
Some sources suggest that the best time of the year to remove moss from roofs is early spring, when seasonal rains provide the moisture that the plant needs. But you can remove moss from the roof at any time of year. While you should apply moss-killing treatments in spring and fall when the plant is actively growing, it may be easier to brush and hose moss off the roof when it goes dormant in summer and becomes brittle.
No matter what time of year you tackle this project, you’ll want to pick a dry, cloudy day so the cleaning solution won’t evaporate too quickly—and so you don’t slip off a wet roof or ladder.
Tried-and-True Advice
“Don’t make the same mistake I made: I initially used a power washer to get the moss off my roof thinking it would be faster, but all it did was damage the shingles and cause some of the granules to come loose. I would strongly advise against using a pressure washer on your roof. Stick to a gentle, soft brush and water. It’s much safer for your shingles in the long run.”
—Paul Rankin, Contributing Editor and Writer
Step 1: Remove loose moss from the roof.
Make sure your safety gear is in place. Working from the top of the roof or from a ladder, use a garden to spray the moss off the with water; spray the moss off at a downward angle. Then, use a long-handled soft-bristle scrub brush to clear away loose moss. Work from the top of the roof down to avoid lifting shingles, and brush gently to avoid damaging them. Work on one section at a time.
Pro tip: Never use a pressure washer on a roof, especially on asphalt shingles. The force of the water can loosen the shingles, and drive water between and beneath them.
Step 2: Apply a moss remover.
A light scrubbing probably won’t remove all of the moss, and even if it does, you may be left with unsightly stains. This is where chemicals, either commercial or DIY solutions, come in. Cleaners can damage plants and discolor other surfaces, so spread plastic sheeting below the roof line, or at least hose off nearby plantings and surfaces before and after you apply the solution.
- If you use one of the DIY roof cleaners mentioned above, hose down the roof, spray the moss with the solution of your choice, wait 25 to 45 minutes, scrub the moss, and then hose the roof down again.
- If you use a commercial solution, follow the manufacturer’s directions for application. Some liquids need to be rinsed off after application while others should be left on. Granular products are generally left on the roof so that rainwater can distribute the moss-killing chemicals down the roof’s surface. Powdered products are usually sprinkled along the roof’s ridge, from one edge of the roof to the other; some require parallel lines of powder spaced 2 to 3 feet apart.
Step 3: Take steps to prevent future moss growth.
Depending on the approach you choose, it can take weeks or months for the moss to die off. Making roof moss removal even trickier, moss can lie dormant in dry weather only to spring back when rain returns. Here are a few things you can do to make sure moss stays away:
- Make a visual check of your roof twice a year (spring and fall), remove debris regularly, and deal with moss promptly.
- A moss problem is a moisture problem, so figure out how to keep your roof dry and increase the amount of sunlight that hits it. For instance, prune trees that are shading your roof, and keep your gutters clean so water can flow off freely.
- Install zinc or copper roof strips just below the ridge cap on both sides of the roof, nailing the strips down every foot or so. (You can also purchase sheet metal in rolls and cut it into 2- to 4-inch strips.) How do these work? Rainwater draws tiny particles out of the metal, and these travel down the roof to kill moss and fungi. Note that these strips need to be replaced every 5 years or so, and they have less of an effect further down the roof. Also, while the Asphalt Roofing Manufacturers Association is in favor of using them on new roofs, it advises against installation on existing roofs because of the potential for leaks down the road.
- If you live in a moss-prone region and a new roof is in your future, think about using algae-resistant roof shingles. These pricier options incorporate copper granules that can prevent algae from building up on the roof. While they target algae, not moss, they may help make the roof less hospitable to the moisture-loving plant.
When to Call a Professional for Roof Moss Removal
If you’re not comfortable with the idea of climbing on the roof, if you’ve treated your roof and the moss keeps coming back, or if there are parts of your roof that you can’t safely reach, call a professional to help with moss removal. They’ll have the right equipment as well as access to commercial-grade moss-control products that can clean your roof effectively.
Expect to pay anywhere from $450 to $750 to have your roof professionally cleaned, depending on the extent of your moss problem, the size of your roof, and the types of cleaning products the job requires.
