HEALTHY ROOFS YEAR AFTER YEAR
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Once you have decided to install a cedar shake roof, you have a number of options in the style of shake to be used. Choosing can be a bit difficult, and in my experience, your choice can make a big difference in the cost per year of roof life.
I have observed many types of cedar roofs over a 21 year period, many of which I have been actively repairing things that go wrong. As a result, I'd like to pass on to you my conclusions, from the perspective of value for money spent.
For general information on the question, Why don't Cedar Shakes last like they used to?, please see our FAQ page.
All discussion that follows assumes the shakes are Cedar Bureau labeled Number One.
The most popular kind of shake in use today is called the Tapersawn. It's sawn on all sides. In my experience, assuming all choices available are Number One grade, and shingles are not under consideration, the tapersawn is the worst choice to make today. They do not last well. There are two reasons. First is the fact that all the cells in the wood are sawn through, leaving no tough cell walls to help resist rot. Second, a shake that is sawn on all sides can be cut in any direction, and the shake can look fine, but not be edge grain.
Edge grain is important, because it offers the most resilience. The grain should run straight down the shake, with no blemishes or variation, and not on an angle or wave. The converse, cross grain, is a weak piece of wood, which will snap off along the tree's growth rings. In my experience, unfortunately, many tapersawn shakes of #1 grade are not properly edge grain, and some are very bad.
Looking at the photo to the right, showing the cells cut through, it is easy to see how nature will attack the cells, weakened as they are by the fact they are cut open.
Now, please look at the dark line near the top of the photo. This is a line upon which the wood will split between the cells, leaving whole cell walls. You can see clearly how the cell walls offer protection against the deteriorating forces of nature.
So why not go to a heavy split, resawn shake? Here is my experience on that question. A heavy, spilt shake is hardy, with excellent edge grain on the top. However, it is cut on the underside, to create a triangular shape. The sawn portion leaves exposed wood cells, cut through. But the most important thing about this saw line is what it does to the hardiness of the shake.
At the bottom, a heavy split shake is very impressive. However, it is cut to taper to nothing at the top. The higher you go on the shake, the thinner it is. One might say this means little, when an 18" shake only has 7.5" exposed on the roof. However, each shake has two edges, and each edge must leave a gap of 3/8" to 5/8". This is called a keyway, a space between shakes, and in this area, the shake is exposed for 15" out of its 18" length. Fully 83% exposed!
Therefore, it gets weathering very close to it's thinnest point, and in addition, debris tends to accumulate here, just like plaque in your teeth.
In addition to all this, a heavy, split and resawn shake has a lot of variation, by nature, in its thickness. This is of no consequence at the butt, but near the top, it becomes significant, and the occasional shake is weak and thin at the top of the "keyway".
There are many other kinds of shakes, and for deeper study, you can follow two links:
Once you absorb the above information, you will see why I consider shingles, which are always sawn on all sides, and always thinner than shakes, not to be under consideration when economy is a priority.
The shake I recommend is called the Straight Split (Commonly called a Barn Shake). Every time I see a straight split shake roof I find a more resilient roof. Why? I have discovered three important reasons. One, they are always edge grain. It's very difficult to create a cross grain straight split shake. Two, they are of uniform thickness all the way to the top. Absolutely dependably, the tops of the keyways will have at least 3/8" in thickness, which is plenty! Third, the undersides are always split as well.
People generally look at a straight split shake and say, gee, they look thin. But looks are deceptive in this case. They are strong where it counts. In addition to the above advantages, these shakes rarely warp, due to the consistent edge grain. This diagram may help.
Pressure Treated is the best long term value.
Whatever shake you choose, having them pressure treated will add years of life to the shakes. For more info on this process, see the above links.
The average cedar ridge cap in the Lower Mainland is rotten and needs replacement by the time it's 15 years old. When the cap fails, it affects the rest of the roof, because at times, water can be getting under the shakes below, and into the house. This problem mostly comes from the use of ungraded tapersawn caps. Tapersawn caps have all the disadvantages of tapersawn shakes, and they are too important to leave to an inferior wood cut.
If you want a roof that lasts and gives little maintenance challenges, use 24" Split and Resawn caps, Cedar Bureau Labeled #1, Pressure Treated.
That's my advice, based on years of literally sweating, bleeding and risking my life over cedar roofs to make them work properly and give a fair roof life.
If you take my advice, you'll use #1 or Premium Cedar Bureau Labeled Straight Split 18" shakes with use #1 or Premium Cedar Bureau Labeled 24" Split ridge caps, all Pressure Treated and labeled as such.
If properly installed, with proper attention to flashing, roofing felt and attic venting, you should have a hardy, long lasting, good looking cedar roof for 20 - 25 years, and more with ongoing maintenance.
I have no direct gain from steering you in this direction. As an installer, my profit comes from the labour, and not from the materials. One type pays just like another. However, I feel a satisfaction in promoting good value, and of course, this builds goodwill with my customers, as well. So may you be encouraged in your research.
If building a new home, your city probably has a building code that covers your roofing, and a city inspector should provide inspections. This may not be enough, as the level of service from the city tends to vary.
However, if you are doing a re-roofing job, there are no city codes in the Lower Mainland to cover you. You are on your own. Your wisdom in your choice of contractors is your main ally. Then, if you want to ensure fulfillment of basic roofing rules, you have it inspected by a third party.
The Roofing Contractor's Association of BC has a list of Approved Roof Inspectors. If you want to be sure you have a roofing job that is correct, it is an excellent investment to hire one of them to do a couple of inspections through the course of the roofing job. I recommend you have it written into the contract with the roofer, that the roof will pass these inspections, or corrections will be made by the contractor at his expense.
I hope this is of help to those seeking to know more about this important topic.
Yours truly,
Gregg McBurnie, Approved Roof Installer
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