Our rental property has a 17-year-old cedar shake roof of about 1300 sq ft. The house is in a residential neighborhood of single-family homes with very little shade, and when the sun hauls over the horizon it blast the roof with UV for at least 12 hours. We've never had a problem with hurricanes or tropical downpours or any other roof damage.
It was built with thick/heavy shakes and extra underlayment cloth (for ventilation). There are no tricky crickets or corners, just a few valleys and drain system vents. It was put on by a company that we've used for a number of jobs over the last 25 years, and they have a good reputation with other local contractors. This is a small island, and bad news travels fast.
All of the roof gets sun so there's never any mold or mildew or moss or other visible staining, and the roof is a dark brown with maybe a slight grayish tinge. The shakes are still intact with no splits or cracks or eroded butts-- hardly weathered at all. I'm on it once or twice a year to check the gutters or paint the trim, and the shakes always look good.
Perhaps the roof is in great shape because (at the roofer's recommendation) we've paid them to spray it with linseed oil every four years. They also check the shakes and do minor repairs during the spraying, so it's a feel-good maintenance morning. Usually the roof is in fine shape and there's nothing to do.
The cost of the treatment is about two weeks' rent, and in the last 14 years we've had a total of two months' vacancy. There's no reason to shave down the cost by stretching out the treatments, but I'd like to know whether there's a better way. For example this article (
http://pnwhandbooks.org/plantdisease/pathogen-articles/nonpathogenic-phenomena/care-and-maintenance-wood-shingle-and-shake-roofs) seems to imply that the linseed oil isn't very effective. However its references are fairly old. On other sites & forums, linseed oil seems to be one of those topics that evokes roofer debates in the same way that financial forums debate paying off the mortgage.
The next time I talk with the roofer I'll ask whether there are other chemicals in the linseed oil or if it's just the oil. Are there any new treatments for cedar shake roofs, or is the linseed oil "good enough"? Are there any miracle preservatives or other relatively environmentally-friendly additives or substitutes? Is four years a generally accepted interval, or are there different criteria? If you have a shake roof, do you do anything different?
