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Deep-Energy Retrofit: Insulating the Roof or Ceiling?

Thom_W | Posted in General Questions on

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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Replies

  1. the74impala | | #1

    If you want to drive north 2 1/2 hours or so to see the craziness I am doing to my house, maybe that would help you. I am no "expert", but I think I will end up with a nicely efficient home whenever I finally get done. P.s., you aren't Northern Wisconsin, you're down south.

    1. Thom_W | | #2

      Tom, that's great! I'm definitely clicking through some of your posts and seeing some of what you're doing. I'm definitely not "up nort" like you, but everyone else seems to call the GB/Appleton metro areas "Northeast Wisconsin (NEW)", and wanted to specify since contractors in the Madison/MKE markets might consider me outside their service areas.

  2. brian_wiley | | #3

    Hi Thom,

    I totally get where you're coming from about doing a deep energy retrofit in stages. It seems confusing at best. One of the more recent BS+Beer shows was about just that, and was really helpful in terms of thinking about how to structure things, particularly when it came to the roof.

    The part where Jesper became a bit nervous relative to the air-sealing details at the ceiling and added Intello at a later date seems particularly relevant to your situation.

    https://www.greenbuildingadvisor.com/article/the-bs-beer-show-two-deep-energy-retrofits

    1. Thom_W | | #10

      Thanks for the link! I'll give it a watch when able.

  3. mathiasx | | #4

    Have you talked to Paul Kuenn? He’s in the Appleton area, and frequents here.

    I’ll add my 2 cents: if you have enough height in the existing attic, then clean it up (if it’s old fiberglass batts, they tend to be dirty and full of all sorts of nasty stuff), air seal and put caps over any electrical boxes / can lights, and add baffles at the edges to prevent wind washing. If there’s enough room at the edges, you can add baffles from inside the attic. (Sometimes ranch roofs aren’t steep enough to reach it from underneath —then you’d want to add it from the top when they redo your roof.) If everything can be done from inside the attic, you don’t have to wait for re roofing, and any Focus On Energy contractor familiar with blowing cellulose in an attic should be able to do all this work.

    1. mathiasx | | #6

      I guess it depends on what you’re after for “superinsulated” roof. I think R60 (~20” to be safe) is plenty or “pretty good,” but the rafters probably don’t have 20” at the edges, so R value would be lower there. Anecdotally, we were able to do R60 cellulose in the “middle” of the attic (and obviously lower at the eaves) and I haven’t seen frosty corners on the exterior walls upstairs in our 1920’s Milwaukee bungalow.

      1. Thom_W | | #8

        And I appreciate your feedback that the airsealing plus thick cellulose above the ceiling can be effective enough in this climate zone in my building style.

    2. Thom_W | | #7

      Wow, no I was not familiar with Paul, and am sad he hadn't come up in any of my searches previously. I found his website, and I'm REALLY liking what I see and am certainly going to reach out to him for his consulting services!

      I appreciate your 2-cents. That's the route I've been leaning, but I just wanted to make sure to think my decision through before regretting and wishing I'd conditioned the attic and moved the insulation up. But that's looking to be too much of a non-standard approach for this area — certainly expensive, and possibly risky. That being said, I'm a tinkerer, a former electrician, and love doing work to my house. The thought of an attic without itchy batts or a couple feet of cellulose so I can run a new Cat6 here, install a new light fixture/switch there, add/remove/move an interior wall, etc. is quite tantalizing.

  4. charlie_sullivan | | #5

    If you want to go all out on making it super insulated without doing weird stuff that your local contractors find confusing, an option to consider is to remove the whole roof, replace it with "raised heel" trusses so there's plenty of room for thick insulation and ventilation, air seal ceiling plane really well, and then blow R-80 or so worth of cellulose in there. You can specify trusses that will take a higher snow load than your current rafters, which might not meet modern code for snow load.

    1. Thom_W | | #9

      Thanks for the suggesting and tossing yet another option at me to further complicate this! I kid.

      Decapping the house and adding a replacement roof system might be an impossible sell to the Mrs. I've gotten her onboard with some pretty drastic house improvements and such, but if she were to look up and see nothing but sky, I think that crosses the line of "we should have just torn it down and built a new house!" But you do make an excellent point of the snow load limits of the current 2x6 rafter assembly since the pitch is somewhat mild (4/12, I think).

  5. jonny_h | | #11

    I'm in a similar boat (zone 5, 2x6 rafters), and decided to go with the split insulation approach -- 6" external polyiso foam and 6" internal fluffy insulation. I was a little concerned with the detail required for properly air-sealing to make an unvented attic work, but in the end decided on this approach since I need to re-roof anyway, and have some low-slope areas where I wouldn't be able to get more than 8-10" of insulation in a large area internally. Planning on improving things somewhat in stages -- do the roof insulation now, and add new overhangs / overhang the insulation a few inches / leave accessible tails to interface with the WRB for future wall external insulation when it's time to re-side.

  6. PAUL KUENN | | #12

    I'm onto the story now! Thanks Matt for letting Thom know I'm here for anyone that wants to listen. Although it's the stupid things that drive me mad like 4:12 pitches where we occasionally get 80-100" in snow, we just have to live with it. After some long e-mail sessions with Martin long ago, we decided it was best at the time to use closed cell foam from the top wall plate inboard until we could reach at least 16" of cellulose depth. So at the outer perimeter I only have about R18 but it goes up fast every inch inward. Rafter's bird cuts only gave me 3" to insulate at the perimeter edge.

    Now that I do more unvented retrofits with exterior roof insulation, I wished I had done it on my home. When it's -20F the upper walls feel darn cold. I don't want to go there now with the Ecostar tile up there. Yikes!
    Cheers, PK

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