Deep-Energy Retrofit: Insulating the Roof or Ceiling?
My wife and I are young, and our 1970s single-story ranch home will likely be our forever home, so I’m wanting to complete a deep energy retrofit, or at least as much as is realistically feasible to drastically improve the comfort and energy efficiency of the home longterm. It’s not something we can do all at once, but it’s something I want to do in phases, probably throughout the next decade. When it comes time to re-side?—we’ll add exterior insulation. When it comes time to redo the roof?—that’s where I’m running into a bit of conflicting information, or at least options that make me unsure how to proceed.
A chainsaw retrofit to remove the rafter tails sounds, on the surface, doable. That’d allow a continuous blanket of exterior insulation that can be monolithically airsealed — a huge plus. But, we live in a cold-weather climate with humid summers where attics are conventionally unconditioned and vented through the soffit and to the ridge. The roof rafters are only 2×6, 16″OC. I have no mechanicals or ducting in the attic, and don’t typically use it for storage of any kind.
For my situation, how do I know whether it’s best to leave the attic unconditioned and airseal + superinsulate above the ceiling, or whether it’s a better idea to bring the insulation and airsealing up to the roof? While the latter seems more the “if you’re going to do it, go big” solution, I have a lot of trepidation with getting the vapor permeation and roof venting designed property for our climate zone. Questions such as: How much exterior foam would be needed? [https://www.greenbuildingadvisor.com/article/calculating-the-minimum-thickness-of-rigid-foam-sheathing] What, if any, insulation would be appropriate in the rafter bays to address moisture collection or vapor infiltration/exfiltration? [https://www.greenbuildingadvisor.com/article/getting-insulation-out-of-your-walls-and-ceilings] How would I construct an air gap to vent the roofing material? [https://www.greenbuildingadvisor.com/article/how-to-install-rigid-foam-on-top-of-roof-sheathing]
Or do I just quit trying to reinvent the wheel and have our attic blown full of lots of insulation and let any ol’ roofing contractor do what they’re comfortable with? I’m definitely a homeowner stuck in this trap: [https://www.greenbuildingadvisor.com/article/roofing-and-siding-jobs-are-energy-retrofit-opportunities]. I haven’t been able to find a contractor or consultant locally who would be knowledgable or specialized to design or perform this project, so I’m left researching, planning, and staging this myself. If anyone can recommend a Northeast Wisconsin contractor/consultant for the job, I’m all ears! All I can find are roofing & siding or general contractors who have no experience with this, or insulation and energy audit companies who don’t do much more than blower door tests, air sealing, spray-foaming of rimjoists, and blowing insulation into the attic or walls.
And a big kudos to M. Holladay and others for the crazy amount of good information and articles and comments on this site!
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