Low-Slope Shed Roof Construction Questions
Howdy all,
I’ve been surprised to find very little information within the FHB archives regarding Shed Roof construction methods; by shed roofs I’m referring to single-pitch roofs. These are very common in the modern/contemporary aesthetic… specifically, single pitch roofs around 2:12.
I’m curious for insights on best practices for insulation on a 2:12 shed roof. I know there are 3 options: Exterior rigid insulation (unvented), Hybrid insulation above and below (or CCSF against underside of sheathing, also unvented), and vented with air-permeable insulation in the framing cavity. I’m just curious people’s opinions on best practices here… TJI framing vs. solid sawn, parallel chords, SIPS, etc. Has FHB ever done a real analysis of this roof type? Certainly seems worthy of a feature article, because it is a very common design, and there are certainly many ways to do it incorrectly.
Thanks for any leads, tips, or opinions of best practices!
Aaron
Replies
I'm presently building one. It's a small shop on my property with 2:12 unvented in zone 5b - southern Colorado front range. My understanding is that vapor drive should be the deciding factor in how you insulate. I'm doing hybrid 4" xps and epdm on top with r-19 batts below. In a colder climate, I'd probably want to insulate all outside. When using a/c in a hot climate, I think you can get away with more insulation inside if you're venting. But ordinary venting doesn't really work well with 2:12 slope, so you're better off going all outside. In any case, low slope ends up being unvented unless you're doing some exotic venting, which kinda defeats the simplicity of a shed roof.
If I'm not mistaken.
I also had some constraints: on my small property I wanted to limit overall height of the structure so as not to block winter sun into my adjacent house. At the same time I wanted as much interior height as possible. Xps is also expensive.
If and when I build my dream house in the woods, I'll likely do a low slope roof with i joist rafters, slap 12" of xps on top and call it a day. Regardless of climate I think this is the best way to do a light frame roof.