How To Look At A House
McGarry and Madsen's home inspection blog for buyers of
site-built, mobile/manufactured and modular homes
Can vinyl lap siding be installed diagonally?
Monday, July 8, 2019
It does not seem like such a good idea to us, but at least one manufacturer we found has a detail for installing the transition between vertical (or, in this case, semi-vertical) vinyl lap siding and horizontal. Here’s the installation detail recommeded by PlyGem.
Unfortunately, the installation shown in the photo above uses a single J-channel, while the recommended installation diagram specifies two J-channels back-to-back, undersill trim under the lower one, and flashing between them. Here’s a close-up of the transition area, which is definitely less than adequate.
It’s important to note that vinyl siding is not designed to be waterproof. According to the Vinyl Siding Institute, a national trade organization, “vinyl siding, insulated siding, and polypropylene siding are exterior claddings, not water-resistive barriers, and are designed to allow the material underneath to breathe. This factor provides a supplemental rainscreen that reduces the amount of water that reaches an underlying water-resistive barrier.” But sloppy installation means that more than a little water will get behind the “supplemental rainscreen"—and eventually cause a problem.
Also, see our blog posts What do you look for when inspecting vinyl siding? and Can vinyl siding be painted?
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To learn more about exterior walls and structures, see these other blog posts:
Photos - Ben Michler, Diagram - PlyGem
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