Pressure Washers’ Guidebook Update 2023: Cleaning and Sealing Cedar Shake Roofing

Pressure Washers’ Guidebook Update 2023

What’s “Up” on the Rooftops? Cleaning and Sealing Cedar Shake Roofing

Published November 2023

Photo courtesy of Mike Hilborn with Roof-to-Deck Restoration


Cedar shake roofs are popular throughout most of North America on both residential and commercial structures. They are found almost anywhere that would also commonly have wooden decks and fences but are more prevalent in heavily forested and humid regions, as compared to more arid climates or heavily populated urban areas.

Historically speaking, cedar shingles/shakes have been one of the most popular choices in roof coverings because they are readily available, are aesthetically pleasing, and if properly installed and maintained, will last 40-to-60 years. Without proper maintenance, however, they tend to only last about 20 years. Many homeowners are not aware that they need to keep their cedar shakes clean for them to last.

That said, the decision to pressure wash or soft wash cedar shakes is a controversial one. Some shake manufacturers and industry associations do not recommend either, so companies looking to add this option to their service offerings must do their due diligence before setting foot, water, or chemicals on a cedar shake roof! When it comes to cleaning cedar roofs, it’s not a case of “buyer beware.” It’s more a matter of “service provider be aware!” In this update, we’ve provided insight into both washing methods and trust that pressure washers will educate themselves on the best option for their geographical region; the most current methods, chemicals, and technology available; and the unique challenges presented to them.


According to the “Wizard of Wood,” Everett Abrams, president of Shamong, NJ-based DRP Enterprises/Deck Restoration Plus, cedar shakes don’t decay on their own.

“Decay happens as a result of moisture,” explains Abrams.  He notes, 

Modern cedar shakes are laid on top of an underlining that prevents water from getting into the home. Cedar shakes are soft and porous, and when it rains, they retain moisture and swell. Trapped moisture leads to organic growth, such as algae, moss, lichens, fungi, or mold. If left on the roof, those growths eat away at the shakes, exposing the underlining, which then destroys the water barrier. Ultraviolet light can also damage the roof’s underlining if the shakes are not there to protect it. Cleaning off organic matter is critically important to extend the life of the roof.

Abrams adds that it typically takes about 10 years without cleaning for a homeowner to notice organic growth and graying discoloration on cedar shakes. Even after years of neglect, a good cleaning followed by regular maintenance (typically every five years or so) will solve the problem and help extend the life of the roof.

Homeowners should be advised by their installer to eliminate the causes of debris accumulation and mold and moss growth by removing all overhanging branches and, if necessary, trees that encroach on the roof. The original shake installer sometimes interlays a zinc or copper strip at the ridge cap/vent. This can be effective for controlling the surface growth of algae, mold, and moss for a short distance down the surface of the roof.

Photo courtesy of Kleen Roof & Exterior Cleaning


“The most important thing you need to know is that soft woods like cedar are very, very sensitive to cleaning,” states Mike Hilborn, owner of Roof-to-Deck Restoration, based in St. Paul, MN.

“If you don’t know what you’re doing, it’s easy to ruin wood using a pressure washer,” he adds. “Whether you elect to soft wash or pressure wash, seek formal training or find a consultant to guide you. Training may be offered both online and at annual conferences through the Power Washers of North American, (PWNA) and the Cleaning Equipment & Trade Association (CETA), as well as through some equipment suppliers and distributors,” he recommends.

It is also recommended that you learn more by downloading the Cedar Shake and Shingle Bureau’s Cedar Roof Care & Maintenance brochure for complete topical treatment product guide-lines and much more at www.cedarbureau.org/wp-content/uploads/2019/04/CSSB-caremaint-brochure-2018.pdf.

Cleaning methods aside, be aware that working on rooftops can be dangerous. When walking on the roof, OSHA-approved PPE must be worn, fall protection may be required, and extreme care must be taken not to damage shakes by walking on them too much, using the wrong chemicals, or applying too much water pressure.


“The application of a cleaning solution with minimal impact pressure is the best definition of the soft wash method,” explains Michael Hinderliter, president of Powerwash.com in Fort Worth, TX. He remarks, “The intent is to reduce or eliminate potential damage that may be caused from high water pressure.”

The soft-wash method became an option for roof cleaning in the late 1990s because it reduces the possibility of unintentional damage to a near-zero probability. As service providers learned more about it, they discovered that it can be more cost-effective (requiring less investment in equipment), time efficient, and environmentally friendly because it uses less water. And we all know that water today is a most precious resource. Simply put, with the advancements in chemicals and non-pressure cleaning equipment, soft wash cleaning will not damage the soft cedar wood. 

“While the use of a power washer to clean cedar roofs was the way to go in the past, it is no longer advisable,” advises Dave Dykstra, owner of Michigan-based Kleen Roof  & Exterior Cleaning. “With a pressure washer, the top layer of the cedar fibers are removed along with the organic growth. With the soft-wash method, this layer of the cedar is not stripped off. It’s the cleaning agents that are doing the work to remove the organic growth. The rinsing with soft wash is completed with hose pressures of below 100 psi. We use a booster pump and run our pressure at 65 psi.

Photo courtesy of Kleen Roof & Exterior Cleaning

“Also, if a pressure washer is used, workers will need to walk the whole roof, as every shingle needs to be hit with the wand,” adds Dykstra. “This requires being tied off at all times or the use of a lift. With soft washing, almost all cedar roofs can be cleaned from a ladder or the ground.

“Humid climates or heavily forested areas, like Michigan, lead to much thicker moss growth on the cedar roofs than what one would see in the south. The chemicals kill the organic growth, and the rinsing removes it. Sometimes, depending on the thickness of the growth, two or three treatments and rinses may be required.

“While you may see some references that say, ‘Don’t use bleach on cedar,’ sodium hypochlorite (commonly known in a dilute solution as bleach) is, in fact, safe to use on cedar roofs,” confirms Dykstra. “After cleaning, treating the whole roof with oxalic acid (rather than sealing) will bring the color back to the cedar and leave it looking like new. It’s not just sodium hypochlorite and surfactant alone that will clean cedar really well. We have developed our own mixture at Kleen Roof that gives us great results. Many distributors offer specially formulated products as well.”


“There is no choice for cleaning asphalt roofing, for example,” states Hinderliter. “Pressure washing will damage it, so soft washing must be performed. As for other structures, it comes down to which method will be the most cost effective and still achieve the desired results.”

“That said, the reason you are called upon to attend to a cedar shake roof is to clean it,” adds Hilborn. “If it retains moisture due to a build-up of organic matter, it will rot faster. In most cases, removing this debris requires the use of some force and the ability to work up on the roof. Some companies use brooms and brushes to clean. I feel this isn’t as thorough. At Roof-to-Deck we still use pressure washers to get algae, moss, and lichens off.”

“I believe that the choice whether to soft wash or power wash is a preference that is closely related to your geographical region, your experience, and what type of roofing challenges you are facing,” concludes Hilborn. “In our area, we deal less with sun damage and more with organic matter, so we stick to power washing. We are on the roof walking top to bottom, not only cleaning and sealing but also replacing shakes and examining everything. That puts a lot of emphasis on the need to use safety equipment such as rappelling lines, fall arrest harnesses, anchor points, and proper anti-slip footwear. With soft washing you’re on the ground with extension ladders and wands to access the roof, and you may not be able to assess and repair any damaged shakes.”

Photo courtesy of Mike Hilborn with Roof-to-Deck Restoration


Most importantly: Whether cleaning or rinsing, remember the sensitivity of the soft wood fibers. Do no harm.

Trees should be cut back so they do not hang over the roof and cause additional moisture damage. (The homeowner should arrange for this in advance of your scheduled cleaning date.)

To avoid wet flying debris, use a stiff bristle brush to dry sweep areas where large amounts of loose debris, such as pine needles or leaves, have accumulated. (Do not attempt to dry sweep moss or lichen as you will take wood fibers with it.) Note that this is not an effective way to remove moss or lichen. You may be able to remove some of it, but the root system will remain intact. 

Move patio furniture, grills, etc. away from the home to clear obstacles from the path of the contractor and to reduce cleanup time.

Cover any vegetation, statuary, etc. and ensure windows and doors are closed to protect from overspray.

Good technique always begins with attention to safety. Use your PPE! Wear goggles or a face shield for protection from airborne debris and slip-resistant Korkers (footwear) or similar safety shoes if walking on the roof.

If you will be on the roof, follow OSHA regulations regarding approved harnesses, ropes, and fall-arrest equipment. Use your own ladders and equipment, all of which should be of good quality and in good condition.

When working on the roof, always be aware of where you are. Moss-covered roofs are slick, and doubly so when wet. Take every necessary precaution. No job is worth the kind of risk that goes along with carelessness on a roof.


• New shakes, a shake pry bar, and a nail gun—for damaged shake replacement

A cold-water pressure washer with a standard unit 2,500–3,000 psi capability, but use only 1,000 psi (or less) at four to five gpm. Your goal is to use the lowest pressure that gets the job done

A variable pressure, dual-lance wand with 25- and 40-degree tips

At least 100 feet of hose and a sprayer, such as a Sure Flow product

Chemicals: sodium bicarbonate and oxalic acid. Prepare to use your power washer to apply sodium bicarbonate diluted with water through a chemical injector Water to product ratio is approximately two cups per five gallons of hot water. (Hot water will dissolve more powder.)

Photo courtesy of Mike Hilborn with Roof-to-Deck Restoration


New shakes, a shake pry bar, and a nail gun—for damaged shake replacement

At least 200 feet of hose with a wand powered by a 12-volt pump, as well as a pump sprayer for touch-up areas

Chemicals: sodium hypochlorite and surfactants

A booster pump, or some other type of pump that will allow you to rinse the roof with no more than 100 psi


To avoid making spray patterns and test the efficacy of your washing solution, experiment in a small, inconspicuous area with different dwell times and cleaning techniques to determine the gentlest possible approach. Then, use that approach.

Gently power wash the roof starting at the peak and working to the bottom, but spray the shakes following the wood grain (up and down). Pressure wash—Use either a 25-degree tip for moderately dirty to very dirty shakes with built-up organic matter or a 40-degree tip if the shakes are just gray from weathering. Dwell time should be about 10 minutes. Generally, use the highest nozzle size that will allow the job to be done as efficiently as possible. Many contractors use a 40-degree tip and hold the wand varying distances from the wood, depending on the pressure needed to clean that area. Never use a 15-degree tip (or lower); it will damage the shakes.

Never spray up and under the shakes. Despite the protective underlining, water sprayed up under the shakes may wind up in the customer’s attic or staining ceilings. It can also crack or loosen shakes.

Be sure to clean the butt end of the shakes and get between the shakes into the area called the “shake keyway.” The keyway is the space between each cedar shake, and its purpose is to maintain good run-off and ventilation for the roof, which is critical for extending its life.

Once the roof has been washed, it will need to be thoroughly rinsed with clear water. Siding, windows, plants, etc. must also be rinsed … but you are not done yet!

Examine for any missing or broken/damaged shakes that must be replaced. This service should be part of your original quote. On a typical roof, 5 to 10 shakes may need to be replaced, and you could easily replace them. Any more than 50 would be above and beyond the price, and you may want to subcontract shake replacement.

After the roof has been cleaned, rinsed, and repaired, it should be treated with a wood neutralizer/brightener. Oxalic acid is most often used and is applied just like the sodium percarbonate, using a low-pressure chemical tip and a downstream chemical injector. (Oxalic acid is sometimes referred to as “wood bleach” because of how it reacts with the tannins in the wood, really bringing out the natural color—but it’s not bleach.)

Apply the oxalic acid with a soft wash system pump and wand after the final rinse.

DRP’s  wood and deck brightener, for example, uses oxalic acid along with a proprietary blend of other materials. DRP’s deck brightener will also remove metal stains, such as nail bleeds. If left untreated, these are noticeable, especially when you apply a stain. Be sure to thoroughly rinse the siding, windows, sidewalks, plants, etc. when finished as oxalic acid will damage glass and metal if not thoroughly rinsed. It’s much more difficult to clean up after everything has dried.


Sealing cedar shakes is another part of the service process that is still controversial. Some swear by it. Others warn against it.

“My advice is to never seal a cedar roof,” warns Dykstra. “Sealing the roof will lock in moisture that would otherwise naturally evaporate during normal weather conditions. Cedar needs to breathe, and thus a water-repellant type product, rather than a water proofer, is the best route to follow,” he says.


Northern Exposure: North-facing portions of a roof and those under shady tree limbs will hold water and snow for prolonged lengths of time. Not only does the dampness enable organic matter to collect and cause discoloration, but it also affects drying time during the cleaning process. Note that black areas on cedar shakes are caused by dead wood cells stripped and killed by an organism called gloeocapsa magma in algae. The black outer coating protects the algae from the sun and needs to be removed.

Sunlight: Similarly, some portions of the roof are subject to 40–50 percent more direct sunlight than comparable surfaces. Such exposure to sunlight results in thermal stresses to wood and turns it gray. On a sunny day, for example, surface roof temperature can vary as much as 50°F between the sun-exposed top surface and the damp, shaded underside. Exposure to direct sunlight also affects drying time.


Never give estimates over the phone. Visit each job site to determine site access and what safety equipment may be required. As importantly, you also need to see the roof’s condition in person. Many haven’t been cleaned frequently enough, and they are rotten. If you wash them, they will blow apart. Obviously you don’t want that to happen.

First determine whether the roof is restorable, advises Hilborn. “In some cases the homeowner may have waited too long to have the roof cleaned, and it may be irreparably damaged,” he warns. “Perform two tests in an area that looks like it is in the worst shape—usually on the north side or under tree limbs. While on a ladder, gently lift a shake at the butt end. If it is firm and strong, that’s good. If it starts to crack or quickly break, it is probably not restorable.”

He continues, “The second test is to push your thumbnail against the butt end of the shake. If the shake is firm and hard, it is restorable. If it is soft and mushy and collapses against your thumb, it is probably not restorable. If just part of the roof is not restorable, talk with the customer about having part of the roof replaced and the other part cleaned. That is a much less expensive option than replacing the entire roof.”

Inspect for missing or damaged shakes before giving an estimate; then include their replacement in your costs. Repairs are often a service that is offered when restoring cedar shakes. There may be some missing, some cracked and split, some rotted, and all of them need to be replaced.

However, be forewarned that you may not be covered by your insurance to replace cedar shakes. “As a cleaning company, we are not covered for replacing shingles,” warns Nick Guentzel, co-owner of Midwest Softwash, North Mankato, MN. He points out, “We work with a contractor to do any necessary shake repairs. If you need to locate a reputable contractor in your area, the Cedar Shake and Shingle Bureau can be a good resource. Much like the PWNA, they have a list of member installers to help you find people who do this type of work.”

Professional cleaning of cedar shakes restores color to the wood and, when followed with the application of a brightener, temporarily stops microorganisms from doing further damage. Building owners would much rather spend a few thousand dollars to have their roof cleaned than spend tens of thousands to replace it.

Maintaining a photo gallery of before and after photos on an iPad or tablet conveys professionalism. These are handy when explaining to the customer what is happening to their roof. If possible, get some enlarged photos of the moss growing on a shake clearly showing the damage.


Pricing a cedar shake roof cleaning typically comes down to square footage, steepness/pitches, and the level of organic buildup. If the roof is coated in moss and is still restorable, the project will take longer, and the price should be higher. If the roof is difficult to access or poses other challenges, be sure to increase the price.

The price is about the same for both washing techniques.

A shallow-pitched roof is typically priced around 70 cents a square foot. A standard-pitched roof is typically around $1.50 a square foot.

A steep roof can be $2.00 a square foot.

Note that prices (for both methods) may be higher or lower based on other circumstances and regional variances. Cleaning and brightening should be combined in your quote—not an either/or option—and stress the importance of the two steps to the customer in the quote.


Wooden decks, fences, otherstructures, and siding are all possible ancillaries as is shake replacement.


Assess the fitness of the roof before agreeing to terms with a customer. The customer should know what to expect in terms of results based on the starting condition of the roof … and you should know what is expected of you.

Washing a roof is a very messy and dirty job. Avoid conveying material from the waste stream beyond the immediate job site.

It’s important that the wastewater does not leave the property or be allowed to flow into a storm sewer or waterway. Follow all prescribed water reclamation procedures for your region.

Debris from the roof cleaning is just organic matter (dirt) and does not need to be transported from the jobsite. But if there is lots of it, discuss this with the property owner and make a plan with regard to disposal.


Ensure the customer understands the expected outcome before the job begins. Customers with realistic expectations will not be disappointed.

A few weeks after the job, visit with the customer to do a routine follow-up. Have him or her look at the roof from the ground. Openly compare its appearance with the photos taken before the job started. Take more pictures during this call, noting how long after the job the pictures were taken. Such follow-through keeps communication open and ensures that any problems perceived by the customer can be identified and rectified; it also builds goodwill for ancillary and future projects.



Synthetic cedar shakes were developed as an eco-friendly alternative to natural wood and are becoming more commonplace. They are manufactured to provide a close match in appearance, while exceeding the performance limitations of natural materials. Synthetic products should NEVER be pressure washed at a high temperature and/or PSI because it will strip the protective layering and (possibly) void the warranty. Your best resource is to contact the synthetic product manufacturer for instructions.

Power/soft washing contractors need to understand the special cleaning requirements of this relatively new roofing material. They may look like natural cedar shakes but are not, and this presents a whole new service opportunity for contractors. (And another story!)

Current Digital Issue

Click to read.

Past Digital Issues

Click to read.


March 2024
February 2024
January 2024