What Causes Cedar Shakes & Shingles to Weather?
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:
- 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.
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.
- 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