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Question DetailsAsked on 7/8/2012

Should we treat the cedar roof ?

We are wondering if it is better treat the cedar roof periodically or not. Some suggest treating it, but some are against it as the cedar has its own natural oil for preservation and treating it will do no good.

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2 Answers


The question I pose to you is, would you treat a cedar deck or cedar fence? The answer is probably yes. Then why not treat a cedar roof? Cedar shakes are much more porous being as they are split not machine cut, like a fence or deck board, thus cedar shake absorbs more moisture than a machine cut fence or deck board.

You have to understand that cedar of today is nothing like cedar of 100 years ago. Yes there are natural oils and tannins in the cedar wood which make cedar much more durable to the weather than pine for example, however the cedar we install is often only 50 year old trees... where as the cedar installed only 100 years ago could have easily been harvested from 500 year old trees. The difference is the wood is much less dense now-a-days than it was in the past, making it less weather resistant now, than previous years.

I had a short, maybe 4', 1x8" cedar board sitting in my yard left over from a project. The board is about a year old and I was cleaning my yard this spring and happened to examine the board thinking I would use it for an upcoming planter box I was considering building. The board was pretty weathered, warped to heck (warped beyond practical use) and very brittle, only in one year exposure to weather. There was no rott but the board was useless. Rott is not the only thing one must be concerned with when it comes to wood, because cedar shakes shingles are very prone to cupping and warping when they dry out.

So what if you don't preserve your cedar roof? Quite honestly it is not the end of the world, so long as you understand that your cedar roof won't last as long if left untreated as it will if properly preserved and maintained. Nothing will last as long unmaintained as a maintained counter-part will last. Think about owning a car and never changing the oil. Cedar IS a maintenance roof, but the decision is up to you what level of maintenance you wish to put into it. Leaving the cedar roof un-preserved will mean more maintenance in the form of replacing cupped, cracked and missing shake. You'll always have that kind of maintenance but in my experience cedar roofs left untreated require more of said repair than the treated roofs.

So let's assume for a minute you decide to preserve the cedar roof. Don't waste your money on various products like Thompson's water seal which is a home owner rated product and only lasts two years. Good for decks and fences where it's ez to install, but presuming you will hire someone to do this for you, the cost is mostly labor. Having said that also stay away of acrylic based (water based) treatments, I can name a few that are absolutely worthless, nothing more than sold color stain. A cedar roof needs special preservatives, and we prefer to use oil based preservatives... Not coating, oil based products will penetrate into the shake and revitalize the lost natural oil. An acrylic coating doesn't penetrate and sits atop the wood doing not much of anything at all, except looking pretty "hiding" the defect beneath.

If you do choose to coat/treat/preserve, no matter what product you choose to use, a good washing is recommended on any roof older than 1 year of age. This is because natural vegetative life such as algae will begin to form on the cedar. Moss, lichen and sometimes even mold (though mold is unlikely) will also grow on the wood. Covering this vegetative growth is useless, an absolute waste of money. If the roof is older than a year a washing by someone experienced is mandatory. It's very ez to damage a cedar roof with a power washer, though we use a power washer, we turn the PSI way way down. Also a biocide bleach may be used to help kill the plant growth. This bleach carries with it it's own risks as well so the applicator better be very careful not to kill the surrounding flowers, trees and shrubs.

Furthermore, heavy metal strips such as zinc or copper may be installed to help reduce or prevent future vegetative growth from coming back. While I'd still recommend re-washing the roof before each preservative treatment, this heavy metal may increase the life of the cedar wood because the vegetative growth will be reduced or prevented, and the vegetative growth does help to decay the wood.


Answered 8 years ago by ReliableAmericanRoof


It is true that cedar has it's own natural oil content and is about 3% of the cedar mass. As to treatments, there are many opinions and one that the homeowner needs to research and draw their own conclusion. There is no question that cedar needs to have a maintenance program to reach their full lifespan.

Cedar Roofs Don't Decay... but they do Weather.
In warm, humid climates and on heavily shaded roofs, mildew, moss, algae, lichens and fungi will grow, because these organisms retain moisture, the cedar will decay with time. Thus a cleaning schedule.

The answer above is more detailed and most I would repeat. My point, is to treat a cedar roof is one of choice. To clean a cedar roof periodically is a must. That will go along ways to extending the lifespan of a cedar roof.

The question know comes down to what is your goal, added curb appeal or extending the life of the cedar roof.


Answered 7 years ago by Guest_90269124

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