siding & rainscreen questions
I am in the middle of putting an addition on my house in central Virginia, and trying to decide what sort of siding to use. I have regrettably sheathed the structure with OSB rather than plywood, and I’m interested in taking care to ensure maximum drying potential, given what I’ve read on GBA about OSB’s inferior drying properties.
At this point, the OSB is covered with Typar, taped at the seams. I plan to put a rainscreen of some sort on top of the Typar to prevent sun-driven moisture from infiltrating the wall. I’m planning to use lapped siding, either cedar or fiber cement.
I have two questions regarding this choice:
– It seems to me that cedar would allow more water to penetrate than factory-painted fiber cement siding, but that cedar would also allow more water to escape. Are these assumptions correct? If so, which type of siding, if installed over a rainscreen and properly maintained, would lead to an overall drier wall assembly?
– Is there any advantage to manufactured rainscreens over furring strips other than ease of installation, and, in the case of fiber cement siding, the continuous nature of them that would provide a more supportive substrate than furring strips?
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Replies
As long as you do the venting right - open at top and bottom, with insect screening (or some equivalent), and you've got a sufficient gap behind (3/4" seems to be most common, but sometimes you can get away with less), I don't think there'll be a difference in moisture movement through the cedar vs fiber cement - the far majority of the drying is via the air channels. I might back- and end-prime the cedar before installing it though, just for kicks.
Back prime, done for most climates. Clap boards are self rain screening. Some wraps have issues w/ tannins.
Timothy - VA is in climate zone 4, you should be installing 1" rigid foam on the outside of the wall for thermal bridging and condensation control. A taped and sealed rigid foam will provide you with a second moisture/air barrier; that's cheap insurance.
As far a rain screens, you could look at products like Home Sliker to see if it fits your needs. It's a great product and much easier to install.
In this day and age, if you are using siding, fiber cement siding is the way to go; it gives you durability and very little maintenance.