Cedar shakes are one of the ultimate roofing materials. Perhaps this is why asphalt manufacturers have tried to mimic cedar shakes for quite some time. The color, texture and overall appearance of a cedar shake roof is hard to duplicate. However, as you might expect, this beauty comes with a price tag. Cedar shake roofs require periodic maintenance in order to retain their positive qualities.
Wood, left unprotected, can be easily abused by sunlight and water. Some wood though, contains naturally occurring chemicals that withstand, to a degree, the effects of water. Sunlight, especially ultraviolet (UV) light, readily attacks any unprotected wood.
Sunlight = Trouble
Sunlight, far and away, is the biggest enemy of cedar shake roofs. The UV rays of the sun actually break down lignin (a component of wood cells.) This breakdown occurs on a small scale and, as such, is invisible to the naked eye. This reaction only happens at the top surface of the cedar shake. However, wind and rain wash away the broken-down wood cells and expose a new layer. So the process is ongoing. The color change you see when cedar shakes (or any wood for that matter) turn gray is a testimonial to this physical breakdown of the wood.
UV light also causes another problem. In the process of destroying the lignin, very small cracks develop in the cedar shakes. These cracks allow water, bacteria, dirt, etc. to drive deeper into the wood. This, as you will see in a few moments, accelerates the destruction process.
Natural Preservatives
Cedar is one of the naturally occurring woods that contain high amounts of natural preservatives. The old growth cedar logs cut down 100 years ago tended to have higher amounts of these natural chemicals than the cedar logs of today. This is one reason why cedar roofs at the turn of the century required little or no maintenance.
The problem with these natural preservatives is that they dissolve in water. In fact, these chemicals are often referred to as extractives, because they can be "extracted" from the wood by water and other solvents.
When these extractives are leached from the cedar shakes, another phase of destruction begins. Water can more easily enter the wood cells, causing shrinking and swelling. Fungi which like to inhabit wood can also more easily grab a foothold. These fungi start a destructive process which, when left unchecked, will cause premature roof failure in short order.
Water Tubes
The nature of sawn wood causes it to more easily degrade than an unsawn log or branch. When a tree is living, it really is a collection of tubes, very small ones indeed, that extend from the ground up to the top of each branch.
However, when you saw a tree into logs and then turn it into something like cedar shakes, you partially expose, along their entire length, some of these tubes. Under a microscope these exposed tubes look something like U-shaped valleys or a freshly furrowed field. The depressions are great places for water, dirt, bacteria, mold spores, etc. to get trapped. Other roofing materials such as asphalt shingles, metal, slate, tile, etc. don't have this problem.
Sealants and preservatives can go a long way in temporarily filling these exposed tubes. In this way, you slow down water penetration which in turn slows down the loss of the natural extractive chemicals.
Keeping your Roof Dry
The key to extended life for cedar shakes is keeping them dry. Remember, water dissolves the extractive chemicals. Knowing this, do whatever is possible to remove debris such as leaves, pine needles, twigs, moss, low hanging branches, etc. from your roof. These things tend to hold moisture and slow down the evaporation of water from your shakes.
If building new, consider using as steep a pitch as possible. Low pitched roofs wear out faster than steep pitched roofs, it's that simple.
Periodically check your roof for debris buildup. This simple investment of time will pay big dividends. Your cedar shake roof could quite possibly last a lifetime with just a little care.
