Looking at websites like “This Old House” and “Fine Home Building” leads to contradictory results so let me ask here;
What is the story on installing Cedar Shingle Siding, white or red, directly on a layer of Tyvek?
Some claim tannins in the shingles will cause the Tyvek to degrade, leading to water leaking, if not into the house, at least onto the siding and causing rot. These folk also say the right way to do it is to install a fiber barrier or lath between the shingles and the tyvek.
Others say ‘baloney!’ - they’ve taken down 10 or 20 year shingle installations and seen no signs of degradation, leakage, or other damage. Apparently there is a Western Cedar Foundation which makes no mention of any such problem.
Yet others say shingles can go on tyvek without problem as long as the shingles’ back side are primed.
It seems to me that a properly shingled side of a house, with overlap, and painted, is not going to let water get through to the backside, but I’m no carpenter or architect.
What’s the scoop?
This comes up as we’re about to put an extension on our house and I want to do the right thing.
Unpainted shingles need to be installed on lath so that they can dry. Directly on Tyvek will trap water where they contact each other. Priming them doesn’t mean much because primers may be water soluble and require a layer of paint to seal them. I don’t know why you’d want to paint them, it won’t seal them forever, the paint will peel, the shingles will develop large and small cracks where the are exposed to moisture anyway. They will benefit from oiling, it adds water resistance, makes the wood look better, and helps keep bugs out, and some bugs will eat their way into cedar. Both red and white cedar are very long lasting, white is incredibly durable, mounted on lath that allows air circulation they should last for 50 years. Hand split shakes will last even longer, but cost you more. However, you are talking about siding, not a roof, so in a dry enough climate moisture shouldn’t be much of a problem. Anyway, I can’t tell you how long cedar shingles will last directly on Tyvek, I’m sure not as long as if they were mounted on lath, but maybe way longer than you care about.
ETA: You may want to consider cedar clapboards as an alternative, pretty much the same requirements, but lower maintenance because shingles may split.
you are better off painting or staining both sides anyway to prevent cupping. I repaired my house several times this way and they stayed flat. For thinner stains you can just dip the whole shingle and let them drain.
Dennis