I have a question concerning the proper installation of cedar lap siding. I was taught that wood siding should be installed with rosin paper or felt as underlayment not housewrap. The main reason was to prevent vapor transmission through the wall from accumulating on the backside of the wood siding. Any thoughts. I am in a discussion with the sales rep. Thanks
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All those wraps you mention are permeable to water vapor. The concern with cedar siding has been interaction between the plastic housewraps, notably Tyvek, and the cedar, and the deterioration the oils in the wood cause to the wrap. I've heard that at least with Tyvek this was addressed a few years back, but I don't know for sure.
In any case, you certainly want to backprime the cedar (if not done by the factory) and prime any cut edges before nailing it on. Other good advice to suggest, particularly if you get a lot of rain where you are, is to install the cedar over a drainscreen/rainscreen. This can be in the form of wood strips nailed vertically over the sheathing and wrap through to the studs, with insect screen at the bottom openings. The gap behind the cedar will let rain driven behind the cedar drain freely and not linger behind the cedar. The back side dries faster, prolonging the life of the cedar and paint. The gap also separates the cedar from the wrap, if that is what you use.
Many argue in favor of just tarpaper behind cedar, a proven material. Google up the Univ. of Mass papers by Paul Fissette on the subject. Look also on the Building Science web site for the article on diagnosing/correcting a problem with a house that couldn't hold a paint job very long. Or just wait for all the subsequent posts your post will get here.
There are chemicals in cedar called tannins that leach out and deteriorate most brands of house wrap.
To sort of summarize:
If installing nekked cedar, try to prevent it from being in direct contact with spun-poly housewraps.
If you are installing unfinished claps, then either use a rain screen to hold the clap away from the spun-poly housewrap, or install the cedar in direct contact with tar paper.
If you are backpriming the cedar, then you can install the claps in contact with spun-poly wraps or tar paper. Or you can use a rainscreen.