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.