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Question DetailsAsked on 5/3/2014

I have cedar shake siding directly over plywood. Won't rain get behind the shakes and ruin the plywood?

Especially at the corners, there is separation between the shakes, where it seems like the plywood would be exposed to rain and snow.

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1 Answer

Voted Best Answer

Your plywood should have been covered with tar paper or one of the other house wrap products out there before siding was applied. I prefer products like Tyvek and tape the joints as per manufaturers instructions. I do not know what the exposure is on the shakes on your home but generally they are applied with overlapping layers, much like feathers on a duck. 18 inch shakes would have say a 7 inch exposure so at any given point there are two layers and care should be given to make sure the joints in the layers do not line up. You also can have shakes that are put on with an undercourse of less expensive shingles and can be usually seen with a 14 inch exposure, again care is taken to overlap the joints in the undercourse shingles. The same sort of process is done on the corners with each layer lapping the one next to it. The problem with not at least putting tarpaper on is the wicking of moisture or steam when the sun hits the house and pushes the moisture out the back. It is the same as the problem they are having with the newer stucco and stone products when not applied correctly.

I wonder how you know there is nothing behind the shakes. Did you watch them while they did the job?


Answered 6 years ago by ContractorDon


In addition to what Don said, hosuewrap or building felt (ASTM D226 tarpaper) underneath first certainly, and failure to put a housewrap of some approved sort under them should certainly be a code violation in most areas. It has been found that most synthetic housewraps perform poorly under wood shakes and shingles, so tarpaper is recommended, and ASTM 266, not the light (7-8#) varieties.

Usually shingle/shake houses built by old-time professionals have a protective flashing put on all corners before the shingles - typically 3 or 4" wide to each side. Also, I have never seen a professioanally shingled or shake siding without overlying corner trim boards - usually 1x4's on each side, covering the exposed shakes edges at the outside corners, or a second layer of shakes lapped the other way or as a single custom piece (better) - like in these images -

Just running the shakes to the corner with a simple lap is sloppy and poor practice - an invitation to trouble, because that lap will open up with aging and let water in.

Answered 6 years ago by LCD

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