Cedar or redwood shakes roofs have been around for centuries and are one of the original roofing materials. In early days, the shakes were laid over top of spaced lathing strips that were spaced so the shakes would stay dry. As a result, such cedar or redwood roofs can last for many decades.
Cedar Shakes roofs have a material life expectancy of anywhere from 40 to 60 years but because of the lack of maintaining they tend to last 15 to 25 years based upon the grade of the shakes. This is why you will hear that a cedar roof will last, on average, about 20 years.
The reason for this is that cedar/redwood shakes will not decay on their own. It takes moisture and some form of infestation (moss, mildew, lichen, mold or fungi). Thus the only way to get the full life-span potential from a cedar/redwood roof or siding is to maintain it and have it cleaned.
One problem with cedar/redwood roofs that were installed in the last 30 years is the installation itself. Lath installation is no longer used and they are now installed upon decking with an underlining, or what we call roof felt.
The felt does make for a great water barrier, but because of improper spacing between the felt and the shakes, the shakes often cannot breathe or dry properly. Thus the shakes retain moisture, allowing for infestations to move in.
Over time, the shakes lose their integrity, which can lead to interior water damage and premature roof replacement if there is no regular roof maintenance or cleaning. With a cedar shakes roof, the under felt protect the home or is the water barrier and the shakes protect the felt. So the integrity of the shakes is key to the preserving of the felt or water barrier.
Many cedar/redwood shakes roof homeowners were never told they need to maintain their roof to reach the potential natural life span of anywhere from 40 to 60 years. Normally after a 10-year period of not cleaning, a homeowner will notice the green moss or mold, the lichen or the dark brown to black coloration of fungi.
At this point, many homeowners believe that a new roof is needed, when in reality, a good cleaning will often solve the problem. Once the wood roof is properly cleaned, the infestations and moisture are removed, allowing the shakes to breathe again and stay dry. On average, a good cleaning should last between six and eight years.
In regards to staining and sealing a cedar/redwood roof, staining is fine for curb appeal but adds very little value to preserving the roof itself. Sealing of cedar/redwood roofs should never be done! Cedar shakes need to breathe so they can expand and contract, that is why they are installed spaced. Given cedar has 3% natural oil content, which will leech out over time, some form of oil rehydration should be considered for proper maintenance purposes.
In addition to cleaning, you should make sure there is no debris left in the valleys and no over-hanging trees over the roof as this will cause moisture and shade. Also, it is a good idea to replace any missing shakes that will expose the felt, as UV light can cause felt deterioration.
When properly maintained, a cedar or redwood roof can last for many decades.
As to the cleaning process itself. You have, what is labeled, the three step process and then there is the non-pressure process. One can require the use of some form of pressure and getting on the roof, while the other can be done with garden hose pressure from a ladder. There are different types of cleaning solutions that can be used, depending on the process. We prefer the non-pressure process and have developed our own cleaning solution. Both processes can be very effective.
Cedar shakes roof cleaning is a niche service. We started out as a complete roof cleaning service only. Now 95% of our service is cleaning cedar shakes roofs. As more and more cedar roof home owners become educated to the need to maintain a cedar roof. The demand for our service is constant.
Unlike the other roofing materials, it is well documented that cedar shakes roofs have to be maintained.