Cedar or redwood shakes roofs have been around for centuries and are one of the original roofing materials. In early days, the shakes/shingles 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 would last for generations.
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 cedar shakes lose their integrity, which can lead to interior water damage and premature roof replacement if there is no regular roof maintenance or cleaning.
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 no real value to preserving the roof itself. Sealing of cedar/redwood roofs should never be done as this will keep the shakes from getting the air they need to stay dry.
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 generations.