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Off-grid cabin: Cathedral ceiling insulation?

Ryan906cabin | Posted in General Questions on

Hello,

First off thanks for your help. We have a 500sqft off grid cabin in the Upper Peninsula of Michigan. Currently the inside is down to studs and we need to install insulation in walls and ceiling. Cathedral style ceiling–not vented. The cabin is heated by a wood stove and will be used once a month for 4 nights MAX. As its 6 hours from home. The exterior is barn metal and tyvek. No insulation. We are on a limited budget as this is basically a hunting camp/summer retreat. After insulation we will install pine T&G.

As of right now I am leaning towards cut & cobble 2 inch rigid foam so that I have some sort of vapor barrier. We can not afford spray foam. What other options do I have? Could I do fiberglass batts in walls? Ceiling? The cabin will have limited use.

Thanks!

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Replies

  1. GBA Editor
    Martin Holladay | | #1

    Ryan,
    You have two needs. (a) You need an air barrier, and (b) you need insulation.

    The Tyvek and metal panels don't limit air movement. Cut-and-cobble can work for the walls, but I don't recommend the cut-and-cobble approach for unvented roof assemblies. (For more on this approach, see Cut-and-Cobble Insulation.)

    It's worth choosing a decent insulation method, because this building may be used differently in coming decades. Maybe some day, someone will live there full time.

    If it were my cabin, I would probably install mineral wool batts between the studs and rafters. For the roof assembly, I would leave an air gap at least 2 inches deep between the top of the mineral wool batts and the layer above (roofing underlayment? purlins? OSB?) so that venting could be retrofit if you ever wanted to.

    Then I would install a continuous layer of rigid foam, the thicker the better, on the interior side of the walls and roof assembly. I would install this layer of rigid foam with attention to airtightness. (Foil-faced polyiso is the easiest type of rigid foam to tape.)

    Next comes a layer of 1/2-inch drywall for fire safety (and to act as a durable air barrier). Tape the seams of the drywall with paper drywall tape and mud, but you don't need to sand the seams.

    The pine boards can then be installed on the interior side of the drywall.

  2. Jon R | | #2

    I calculate that fiberglass insulation and MemBrain and exhaust only ventilation would work well. But this doesn't address full-time occupation.

  3. Ryan906cabin | | #3

    Thank you both. Let me give some more details. This is an off grid cabin with no running water, electricity or amenities. At this moment three feet of snow is on the ground and you would have to snowshoe in from the two-track. It will be used one long weekend in April, May, June, September, October a week in November and MAYBE a few long weekends in Dec-March. That is the max! A 6 hour drive, other family activities and limited vacation time make it difficult. I just want to do something that is correct as possible to maintain the integrity of the place. Critters are a huge issue too. Mice and everything else. Previous to the big rehab we are doing we would be in this place with no insulation, a tarped roof and the wood stove would keep us very warm. Since we have tidied things up replacing the rotted wood and exterior materials we would like to add some sort of insulation. Sorry, we can not go back and add vents. Knowing this, would my rigid foam solution work for the price or am I missing out on some other idea? Thanks!

  4. Walter Ahlgrim | | #4

    Maybe I am a stick in the mud but this cabin has survived as is for a long time, given the small number of hours you will use the place and the fact that the fuel is likely dead fall from the property. The safe bet is not to change a thing.

    I think you would get much better bang for your buck with minimal insulation and a good air Barrier say R4 insulation and a layer of drywall with taped seams and then the T&G.

    Walt

  5. GBA Editor
    Martin Holladay | | #5

    Ryan,
    I am very familiar with cabins in the woods that can only be reached with snowshoes. Frankly, you can do whatever you want. We can give you advice on the best way to insulate, but if you can't afford to follow the advice or don't want to do it -- then do whatever you want. It's your cabin.

    Sometimes all you need is a roaring fire in the wood stove and a bottle of Jack Daniels.

    Mice are a problem. Fiberglass batts won't last long in a cabin in the woods. Your cut-and-cobble approach will work, but it's not a great idea for your roof -- especially if the house ever becomes a full-time home.

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