• 515-423-0234

It’s no surprise that cedar shakes and shingles have been used as roofing material in this country for centuries. Their beautiful golden hue and fresh cedar smell (when new) are not the only reasons why people have chosen this roofing material. Other than aesthetics, cedar roofs are often chosen for their insulation and their natural preservatives.

Because of their incredibly low weight and density, cedar shakes and shingles provide a superior insulation over other roofing materials. They do an amazing job at keeping the house warm in winter and cool in the summer. According to manufacturers and cedar shakes and shingle associations, it is the preferred roofing material for areas with extreme cold and snowfall. When properly installed, they keep cold air flowing above the felt barrier rather than letting it seep into the attic. Thus, reducing the amount of stress put on your heating unit, and saving you money on costly heating bills.

Cedar is also a very sturdy and durable wood. It is a flat, straight wood, with a low density and shrinkability factor, which helps to make it an ideal roofing material. In addition, cedar (specifically, Western Red Cedar) contains natural preservatives in it’s fibers. Known as thujaplicans and water-soluble phenolics, these natural preservatives make the wood mostly resistant to moisture, decay, and insect damage.

While cedar makes for a great roofing material, it is important to note that it does require maintenance on the part of the homeowner. As the exposed cedar shakes and shingles weather, and are prevented from having their natural wet/dry cycle, the shakes and shingles will begin to deteriorate. For more information on weathering and maintenance of your cedar roof, watch our videos and check out our Homeowner’s Guide of Maintaining Your Cedar Shake Roof.

All cedar shakes and shingle roofs will experience weathering. Weathering is simply the breaking down of an element (in this case, a cedar shakes or shingle roof) due to exposure to the elements over time. There are three main factors that contribute to a cedar roof’s weathering:

  1. Solar Radiation
    Solar radiation damages the cedar shakes and shingles rapidly, and is the most easily seen. Sunlight will cause the color of the cedar shakes and shingles to change from its natural golden hue to a silvery gray. This color change is an indication that the lignin (the natural glue that holds the wood cells together) is breaking down. As the lignin breaks down, tiny cracks in the cedar shakes and shingles occur which allow excess moisture to creep in and create further damage.
  2. Moisture
    Moisture causes the cedar to swell, and then shrink as it dries. This is known as the wet-dry cycle. After repeated wet-dry cycles, the cracks in the cedar from the solar radiation grow larger and deeper. This means even more moisture will get deeper into the shakes and shingles, preventing the cedar from drying quickly. As a result, the shakes and shingles begin to warp.
  3. Wood-Destroying Fungi
    While cedar contains natural preservatives, these preservatives are depleted over time due to solar radiation and moisture. With the absence of the natural preservatives, wood-destroying fungi (such as white-rot fungi and brown-rot fungi) creep in and start to colonize and grow. In the right environment, these fungi grow rapidly and eat away at the wood. White-rot fungi cause the shakes and shingles to become soft and spongy, while brown-rot fungi cause the shakes and shingles to crack and crumble. Without cleaning the fungi from the cedar roof at the early stages, the shingles and shakes will need to be replaced, and the homeowner risks premature roof failure.

*This article contains information gathered from Journal of Light Construction 1992

Every homeowner wants to hire the right contractor for the job, but how can the homeowner be sure they are hiring someone they can trust? Cedar shakes roof cleaning is no different from any other home improvement project; there are both reputable and shoddy roof cleaners offering their services. Anyone can buy a ladder, a truck, and a washer and call himself a cedar shakes roof cleaner. In order to avoid a scam and hire a professional roof cleaner, follow the rules below.

Say What You�ll Do and Do What You Say

This sounds simple enough, but unfortunately, not every cedar roof cleaner abides by this motto. Don’t just take the contractor’s word for it, take their customers’ word for it. Check their websites for testimonials. Ask for references, and actually contact those references. Look for reviews on the Better Business Bureau, and homeowner repair sites such as Angie’s List and HomeAdvisor. Take the time to find out as much as you can about the roof cleaner’s previous jobs. Be wary of anyone who does not have any testimonials, reviews, or is hesitant to give you more than one reference; there is most likely a reason why.

Better Safe than Sorry

Since cedar shakes roof cleaners spend most of their day up on ladders, they should be insured for the homeowners protection. Don’t just ask IF they are insured, ask to SEE proof of insurance. Don’t take their word for it. All it takes is a call to the insurance company to validate that the roof cleaner is insured. The last thing a homeowners needs is to have a contractor cleaning the roof, fall off the ladder, break his back, and wind up being sued because the roof cleaner’s insurance lapsed.

Knowledge is Power

Cedar shakes and shingles are a unique roofing material that require a specific technique for cleaning and maintenance. The more the homeowner knows about how to properly care for their cedar, the better they are at choosing the right roof cleaner. Do not be afraid to ask the roof cleaner to explain his technique. The cleaning should be only be done from a ladder to avoid accidents and damage. The roof cleaner should never walk on the shakes and shingles. Nothing more than garden hose pressure should be used on cedar shakes and shingles. High pressure cleaners should never be used. Avoid terms like pressure washed and low-pressure, as this can easily damage the cedar shakes and shingles. Ask how they intend to protect the landscaping. The roof cleaner should take the time to protect the landscaping from dirty runoff and any excess water. The cedar shakes roof cleaner should easily and specifically be able to describe their method, and why they use this method.

By following these three rules, the homeowner can be confident that the roof cleaner they are hiring to clean their cedar shakes roof is profession, reputable, honest, and will get the job done without risk to the homeowner. If the homeowner takes the time to find the right roof cleaner for the job, they will be happy with the end results, and know their cedar shakes roof will receive the care and attention it deserves.

We have discussed the reasons you may want to apply a chemical preservative treatment to your roof. Some homeowners may not feel comfortable with the use of these chemicals, and want an alternative treatment. While non-chemical treatments are possible, their effectiveness is not known, and may not provide adequate protection. However, these kinds of treatments are worth exploring.

Non-chemical Treatments:

For those who prefer not to use chemicals, zinc and copper strips could be a safe and relatively inexpensive treatment to control moss and fungi, although it is not a guarantee. Zinc and copper can effectively kill and/or retard the growth of moss and fungi. It could be possible to fasten a 2 inch wide copper or galvanized metal (containing zinc) strip to either side of the ridges and run it the entire length of the roof, as well as across sections of the surface, and below the flashings (unless using copper flashings). It is believed that the rain will leach the zinc and copper from the stips, allowing them to wash across the the cedar, preventing organic growth.

I can not find any scientific study to verify the effectiveness of this technique, and it is unclear as to how much zinc and copper would be required, but I have seen some examples of its effectiveness. In one example, galvanized metal strips placed below chimney flashings appear to be effective for shingles and shakes in that area for the life of the flashings. In another case, on a roof considered favorable for moss growth, two strands of 10-12 gauge copper wire was placed on the roof (one near the ridge, and one about 15 ft. below at the halfway point on the slope), and no moss was seen to grow on the cedar. Again, while I have been unable to find any scientific data on this technique, it looks to be a promising solution for those unwilling to use chemical treatments.

Oil Treatments:

You may see oils that are advertised to replenish the natural oils in the wood. In red cedar, these natural oils account for less than 3% of the total mass. While they do contribute to dimensional stability and decay resistance, applying so-called replenishing oils to weathered shingles may be of little value, especially if they contain no preservative or water-repellent chemicals. However, you might see some temporary benefit, with regard to controlling the cupping and warping of the shakes and shingles.
In my opinion, oil treatments are very limited. Without including an effective mildewcide or other preservative, these oils, such as linseed, may actually encourage mold, mildew, and fungi growth. Furthermore, these petroleum based products oxidize in the sunlight, so they have a very short-lived benefit, and will only increase the flammability of your cedar roof. It is also worth noting that you should never stain, varnish, or seal your cedar roof. The cedar needs to breathe, and it can not do this if a stain or seal has been applied.

One Final Note:

There has been a debate among roofing contractors about the benefits of new cedar over old cedar. In my opinion, cedar is a natural wood and any natural material will be as good as the care it’s given. Your cedar roof is organic and needs to be given special care to reach its natural lifespan before being completely replaced. Just because your cedar roof is old, does not mean it needs a total replacement; most of the time, it just needs a professional cleaning and treatment.

All the information in this series of blog posts came from research from a variety of sources (most notably S.S. Niemiec, former Reseach Assistant, College of Forestry, OSU and T.D. Brown, Professor Emeritus, Wood Science, OSU), and in part from my own professional experiences. These posts are for informational and educational purposes only. While you may prefer to maintain and clean your cedar shake roof yourself, I strongly recommend you hire a professional roof cleaner.

We have discussed the reasons you may want to apply a chemical preservative treatment to your roof. Some homeowners may not feel comfortable with the use of these chemicals, and want an alternative treatment. While non-chemical treatments are possible, their effectiveness is not known, and may not provide adequate protection. However, these kinds of treatments are worth exploring.

Non-chemical Treatments:

For those who prefer not to use chemicals, zinc and copper strips could be a safe and relatively inexpensive treatment to control moss and fungi, although it is not a guarantee. Zinc and copper can effectively kill and/or retard the growth of moss and fungi. It could be possible to fasten a 2 inch wide copper or galvanized metal (containing zinc) strip to either side of the ridges and run it the entire length of the roof, as well as across sections of the surface, and below the flashings (unless using copper flashings). It is believed that the rain will leach the zinc and copper from the stips, allowing them to wash across the the cedar, preventing organic growth.

I can not find any scientific study to verify the effectiveness of this technique, and it is unclear as to how much zinc and copper would be required, but I have seen some examples of its effectiveness. In one example, galvanized metal strips placed below chimney flashings appear to be effective for shingles and shakes in that area for the life of the flashings. In another case, on a roof considered favorable for moss growth, two strands of 10-12 gauge copper wire was placed on the roof (one near the ridge, and one about 15 ft. below at the halfway point on the slope), and no moss was seen to grow on the cedar. Again, while I have been unable to find any scientific data on this technique, it looks to be a promising solution for those unwilling to use chemical treatments.

Oil Treatments:

You may see oils that are advertised to replenish the natural oils in the wood. In red cedar, these natural oils account for less than 3% of the total mass. While they do contribute to dimensional stability and decay resistance, applying so-called replenishing oils to weathered shingles may be of little value, especially if they contain no preservative or water-repellent chemicals. However, you might see some temporary benefit, with regard to controlling the cupping and warping of the shakes and shingles.
In my opinion, oil treatments are very limited. Without including an effective mildewcide or other preservative, these oils, such as linseed, may actually encourage mold, mildew, and fungi growth. Furthermore, these petroleum based products oxidize in the sunlight, so they have a very short-lived benefit, and will only increase the flammability of your cedar roof. It is also worth noting that you should never stain, varnish, or seal your cedar roof. The cedar needs to breathe, and it can not do this if a stain or seal has been applied.

One Final Note:

There has been a debate among roofing contractors about the benefits of new cedar over old cedar. In my opinion, cedar is a natural wood and any natural material will be as good as the care it’s given. Your cedar roof is organic and needs to be given special care to reach its natural lifespan before being completely replaced. Just because your cedar roof is old, does not mean it needs a total replacement; most of the time, it just needs a professional cleaning and treatment.

All the information in this series of blog posts came from research from a variety of sources (most notably S.S. Niemiec, former Reseach Assistant, College of Forestry, OSU and T.D. Brown, Professor Emeritus, Wood Science, OSU), and in part from my own professional experiences. These posts are for informational and educational purposes only. While you may prefer to maintain and clean your cedar shake roof yourself, I strongly recommend you hire a professional roof cleaner.

Now that you have removed the debris from your roof, you can examine the condition of the cedar shingles. Unless there is excessive damage, or your roof is leaking, you should not need to repair or completely replace your roof. In most cases, there may be some staining and discoloration, dirt, and/or organic growth (algae, moss, mold, mildew, fungi, etc.) that can easily be cleaned. Again, I do not recommend you clean the roof yourself. It is a job best left to a roof cleaning professional. While I may go into some detail in these posts, my intention is for you to be as knowledgeable as possible so you can hire a reputable roof cleaner.

Processes for Cleaning your Cedar Shake Roof:

At Sullivan Cedar Shakes Roof Cleaning, we use a proven cleaning solution that I developed after years of hands on experience and research. While I will not go into detail about our solution, I am happy to discuss what a professional roof cleaner should use, based on my research and manufacturer recommendations.

When you hire a roof cleaner, you will want to make sure he uses a non-pressure process, and cleans with a mild detergent solution containing wood preservative ingredients, as well as algaecide, mildewcide, and fungicide. The cleaning solution should also contain an oil to help rehydrate the shakes. Understand that their cleaning solutions may perform differently under various environmental conditions, so cleaning may be needed more often depending on the chemicals used, the amount of area precipitation, average temperatures, and roof conditions.

There are three base ingredients that can be used: sodium percarbonate, sodium peroxide, and sodium hypochlorite. Two of these base cleaners (sodium percarbonate and sodium peroxide) requires the cleaner to walk on the roof and to use a pressure process, which is not recommended.

A few key notes on hiring a cedar shake roof cleaner:

  • Hire someone that is experienced in the use of the above mentioned cleaning solutions. Have them provide examples of their prior cleanings/experience.
  • Have them explain the cleaning process they will use. Find out if they walk on the roof, or if they use a pressure system.
  • Do they carry liability insurance in the event of a fall or damage to your roof? Always have them provide you a copy with their cleaning quote.
  • There should be no need for return visits. Everything needed to clean, treat, and preserve your cedar shakes roof should be included within their cleaning solution.

All three of the above listed products will clean a cedar roof. However, each has its own form of application and cleaning process, so be sure to do your research to find the best cedar shake roof cleaner for you. In most cases, routine debris maintenance and regular cleaning is enough to properly care for your cedar shake roof, but sometimes it is necessary to apply preservative treatments to the cedar shakes. Part 4 of this blog series addresses these treatments.

A Homeowner’s Guide to Maintaining your Cedar Shake Roof

Part 2: Easy Routine Maintenance

In Part 1 of this series we discussed the ways your cedar shake roof can break down and weather due to time and neglect. Let’s now move on to routine maintenance. Keep in mind that I never recommend someone climb on their roof or clean their roof themselves. The dangers of falling and/or damaging your roof are too great a risk to take. It is always best to hire a licensed and insured professional.

A Few Words on Maintenance:

  • Proper cedar roof maintenance starts with keeping your roof dry. If your roof retains water, it creates an inviting environment for wood-rotting fungi to grow. There are several things you can do to prevent this from happening.
  • Remove all leaf litter, pine needles, and other tree debris that accumulates between the shingles, in the valleys, and around the chimneys, as this debris prevents the roof from properly shedding water.
  • Remove overhanging branches that shade large sections of the roof. Shady areas do not dry as quickly as sunny areas.
  • In woody areas, excess branches may restrict airflow to the roof, preventing the roof from drying as quickly as it should. You may want to consult with an arborist about pruning, trimming, or removing problem causing trees.
  • It is also a good idea to keep tree branches from touching and rubbing against the roof. This rubbing can wear sweeping grooves into the surface of the shingles and loosen the fasteners, opening areas for fungi to grow.
  • Look at the trees around your property. If you see excessive growth of lichens and moss, it means excessive moisture is present, and could be on your roof as well.

Hiring a Professional:

Since I do not recommend you climb on your roof yourself, you will want to hire a professional to clear off the debris. Make sure the professional does not use high-pressure washers. Cedar is a soft, low-density wood, and excessive or imprudent use of high-pressure systems can detach shingles or erode many years of wear in moments. Even though this will easily and quickly clean off the roof, you may have done irreversible damage to your roof in the process.

Part 1: Why do I need to Maintain my Roof?

Every week, I get emails and calls from cedar roof homeowners throughout the USA and Canada, asking me a variety of questions about their roof. I find that a lot of homeowners do not fully understand how important it is to maintain, clean, and treat their cedar roof until they start to see leaks. I also get a lot of questions from homeowners asking me if they need to completely replace their roof, or if it simply needs to be cleaned or treated. It has been my experience that most cedar roofs need regular maintenance and cleaning, rather than a complete replacement. While I do not recommend that you clean your cedar roof yourself, I am more than happy to provide you with a series of blog posts with all the information you need to know about how to properly maintain, clean, and treat your cedar roof.

A Quick Note on Cedar:
Most shingle and shake roofs are made from Western Red Cedar (Thuja Plicata). Western Red Cedar is an exceptional wood because it has a defect-free straight grain, dimensional stability, low weight (low density), and is impenetrable to fluids. Most importantly, it is decay resistant because of natural substances found within the wood. Other wood species, such as Redwood (Sequoia Sempervirens) and Cypress (Taxodium Distichum), have similar properties and are occasionally used, but decreasing supplies significantly restrict their production and distribution. For the sake of simplicity, when I mention cedar shingles and shakes, I will be referring to Western Red Cedar. Regardless of the wood type, the maintenance, cleaning, and treatment processes are the same.

Why it is Important to Maintain, Clean, & Treat Your Cedar Shake Roof:
After exposure to sunlight and precipitation, the cedar wood surface begins to change. This change is both physical and chemical, and is known as weathering. As your cedar roof weathers, the first thing you will notice is a color change. The initial red-brown color begins to fade and turn into a silvery gray. This change happens on a microscopic level, and is the result of ultraviolet radiation from the sun stripping the wood surface layer (which is less than 0.01 inch deep) of certain cell-wall materials. This first change in color is rather rapid, and often occurs within the first year of exposure (under severe conditions, within several months). Gradually, the silvery gray will change to a darker, more graphite gray, and eventually to a brown/black color. The color change to brown/black indicates the colonization of the surface by micro fungi (known as white and brown rot fungi).

By nature, wood rapidly attracts water to its surface. When this happens, the wood swells. As it dries and the moisture content decreases, the wood shrinks. This repeated wet and dry cycle causes the development of compression and tension stresses, which cause microscopic cracks to develop. These cracks grow larger over time as they are exposed to more wet-dry cycles. As the cracks grow, they trap water and allow wood-rotting organisms to penetrate deeper into the wood. At this point, the wood becomes harder to dry. With increased moisture, the wood-rotting organisms increase their destructive activity and damage more wood material.

As the roof continues to age, the surface and sharp edges of the shakes and shingles continue to erode because of ultraviolet light and abrasive particles carried by wind and water. In addition, wood destroying organisms continue to slowly degrade the surface. As a result, the roof looks weathered and worn out.

Throughout the years, debris from trees (leaves, pine needles, etc) begin to accumulate in the valleys and between the shingles. As a result, some areas will remain wet for longer periods after each rain. Soon, lichens and mosses begin to grow on the shakes and shingles. At this point, splits develop in the wood, and cupping and curling of the shingles begin to become more apparent. If you are seeing splits, cupping, and curling, expect your roof to start leaking soon. This weathering process can take up to 30 years, but it often happens much sooner if you do not properly maintain, clean, and treat your cedar roof.

Now that you understand what can happen to a neglected cedar shake roof, I encourage you to check out the rest of this five part blog series for more information on roof maintenance, cleaning, and preservative treatments. It is important for you to be as knowledgeable as possible about your cedar shake roof so that you can make the best decisions, and hire the best professionals, to help extend your roof’s life.

Sheryl Brown Rot Fungi 2
Dating back to the earliest days of colonization in North America, cedar shakes and shingles have offered strength, durability, insulation, and beauty to our homes. A wood roof imparts a look of quality that few other roof coverings can match.

Only a few years of exposure to the weather, however, can drastically change this “quality” roofing. Through the interaction of sunlight and rainfall, cedar shakes and shingles can lose virtually all their natural protectants in as short a time as five years. At this age, most cedar roofs begin to show signs of cupping, curling, splitting, and decay. Unlike most roofing materials, however, cedar shingles and shakes can be restored and maintained through proper care and treatment, often doubling or tripling the remaining service life.

Why Wood Roofs Weather

Western red cedar is an extremely durable material even under adverse conditions, but its useful life depends upon the environment. Cedar roofs left unprotected suffer photodegradation by ultraviolet light (sunlight), leaching, hydrolysis, shrinking and swelling by water, and discoloration and degradation by decay microorganisms.

Photo degradation by sunlight. Solar radiation is the most damaging component of the outdoor environment. Photo degradation due to sunlight occurs fairly rapidly on the exposed shingle surface. The initial color change from the golden, orange-brown color to gray is related to the decomposition of lignin in the surface wood cells. (Lignin is Mother Nature’s way of holding wood cells together.) The wood cells at the shingle surface lose their strength and eventually are washed away by rainwater. In addition, microscopic cracks and checks develop, allowing deeper water penetration.

Degradation by moisture. Accompanying this loss of wood fiber at the shingle surface are the shrinking and swelling stresses set up by fluctuations in moisture content. These stresses cause deeper checks and splits to develop. The result: shakes and shingles begin to cup, curt, split, and check at an accelerated rate.
Degradation by wood-destroying fungi. The natural decay resistance of western red cedar is due to its heart-wood extractives, including the thujaplicins and a variety of phenolic compounds. The thujaplicins contribute to the decay resistance of red cedar while the phenolic compounds and resins give cedar its water repellency and lubricity (slippery surface).
Since the natural preservatives in cedar are somewhat water soluble they can be depleted in service. In roof exposure, extractives may leach out in a relatively short time and allow colonization by wood-inhabiting fungi. Aided by favorable climatic conditions, these in turn allow the growth of wood destroying fungi, which ultimately cause the early failure of a roof. The wood becomes soft and spongy, stringy, pitted and cracked or crumbly. This usually occurs first at the butt region of the shingles where they overlap.