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Community and Q&A

Building an A-frame in Upper Michigan

ginnis07 | Posted in General Questions on

We are planning to build a 1250 sq. foot A-frame. The problem is the roof as the inspector is requiring R-49. We know we want it to be well insulated. But due to the roof actually being the walls also…insulating space is an issue. We have already decided to to 2x 12 rafters with 2 inch ridgid on the outside for the roof. Walls are to be 2×4 with again 2 inch ridgid foam on the outside. Has anyone used Protex? Also does anyone one know where to get reclaimed 2″ inch foam in this area?
Any suggestions for increasing insulatin value with cost saving measures would be gladly appreciated. My husband and I are building it ourselves.
Thanks for your input!

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  1. bdrfab | | #1

    Where is Upper Michigan? UP? I know of a place in Illinois to get foam. I happened to find mine on Craigslist. Do a search on here for Unvented cathedral roof assemblies, Martin has written many fie articles o the subject. I would also suggest 2x6 exterior walls, its a really minor extra cost, and will give more bang for the buck IMHO.

  2. ginnis07 | | #2

    Hi, Thanks for the response Aaron...Munising Pictured rocks. Roof must be vented by code...where in IL do you get foam board?

  3. GBA Editor
    Martin Holladay | | #3

    I don't know why you think it is a problem that your inspector is requiring R-49. Your inspector is right.

    Here is more information on building an insulated sloped roof assembly:
    How to Build an Insulated Cathedral Ceiling

  4. ginnis07 | | #4

    I did not think r49 is the problem... the roof being walls in the Aframe is the problem..with the airpocket and 12" rafters..2" on the outside would you get the additional r30 (at least) in the roof/ walls? Please see blue print

  5. bdrfab | | #5

    AH yes, Gods country. Spent 4 years in Houghton back in the day. Loved it. First of all you are in Climate Zone 6b/7a.
    Handy chart for determining minimum foam thickness.
    IMHO, I would try to convince the inspector to allow you to build an unvented roof, and use SIP panels. A 12" panel would give you the R-value you need. Good luck

  6. GBA Editor
    Martin Holladay | | #7

    If you plan to install rigid foam on the exterior side of your roof sheathing, you obviously can't include venting between the fiberglass layer and the foam layer. If you did, you would be introducing cold air in the middle of your insulation.

    If you do want to vent the roof assembly, the vent channels have to go above the foam layer.

    There are lots of ways to make your roof assembly R-49. Just because you have plans that show a low level of insulation, doesn't mean the plans meet code.

    If you have rafters measuring 11.25 inches deep, and you fill them with dense-packed cellulose or dense fiberglass batts, that gives you R-41. To get to R-49, you need R-8 of foam on top of your roof.

    However, according to the way I read the IRC, if you want to have a roof with fluffy insulation under the sheathing, and rigid foam on top, then the rigid foam (in your climate zone) must equal at least R-25. That means that you only need R-24 of fluffy insulation between your rafters. More is better, of course.

    If your inspector wants the roof to be vented, install ventilation channels on top of the foam.

  7. homedesign | | #8

    The Ships Ladder stair will not pass code.
    I don't think this will be a user friendly design to build.
    The cantilevered balcony will be a thermal bridge, difficult to air seal and a flashing "challenge"

  8. ginnis07 | | #9

    Hi John,
    Thanks we have already made corrections to the plan and advised the building inspector..putting in L shaped stairs(where the hall was)..we are taking the wall upstairs all the way out( so no flashing problem). Catilevers we have discussed with building inspector also, to correct. The walk around balcony was the selling put of this plan for us as we have a 10 acre pond and Hiawatha national forest as our back yard. I have always loved a frames..thanks for looking at the plan and giving excellent is much appreciated.

  9. user-659915 | | #10

    The stone fireplace is another major thermal bridge.

  10. GBA Editor
    Martin Holladay | | #11

    I don't like the detail of exposing the 2x8 rafters to the weather. I don't see how you can flash the bottom of the 2x8s, where they sit on the deck beam, to prevent the bottoms of the rafters from rotting.

  11. ginnis07 | | #12

    Hi James,
    We are not putting the fireplace in...instead we are putting in wood burning stove. We have been working with this plan for 3 years...I forget how much we have changed...the downstairs is basically the kitchen and livingroom..with a mechanical room in the center. We put a few more small windows downstairs facing south and no windows or doors on the north side(where the bathroom is no window also entrance). We actually already have the foundation in, crawl and the subfloor in since it is a pay as we go build.

  12. ginnis07 | | #13

    Hi Martin
    We put in a foundation..sorry as I stated to James we have changed alot over the last 3 years working with this plan. We are going to use copper flashing. Actually the building inspector recommended roofing membrame..what do you think would be better?? Also the walls are going to be 3/4 osb at the corners with 3/4 form board all around then another layer of 2 inch form on top. Nailing the foam board or glueing..several different arguments of that still going on. Then house wrap (again on going discussions on which type of house wrap) then furring strips the vinyl siding.Thanks again for all your is helping alot!!!

  13. GBA Editor
    Martin Holladay | | #14

    Even if you install copper flashing on top of the exposed rafters, what type of flashing will you use on top of the deck beam? How will you prevent water from wicking sideways from the top of the deck beam to the seat of the rafter that bears on the beam?

  14. ginnis07 | | #15

    Hi Martin,
    That is what the roofing memebrain is doing..protecting the beam top. The bottom is being covered by copper where they sit on the deck beam. My husband actually wants to cover all with aluminum..but that will change the look too much..

  15. ginnis07 | | #16

    Have you heard of protex?

  16. bdrfab | | #17

    What is it?

  17. GBA Editor
    Martin Holladay | | #18

    Water will still wick into the joint where the rafter bears on the beam, even if there is a cap on the rafter and a cap on the beam -- unless the entire rafter is encapsulated with flashing, which I don't recommend.

  18. ginnis07 | | #19

    Hi AAron,
    Sorry for the delay we had an emergency here last night.
    Prodex 48 Inch Insulation is a foil insulation sold at a website insulation4less. Take a look at it if you get the chance...very interesting. I have already contacted your vendor..we will see how it go's

  19. GBA Editor
    Martin Holladay | | #20

    Prodex is a scam, and Insulation4Less is in violation of the federal R-value Rule.

    They advertise that Prodex, a product that is 5 mm thick (a little more than 3/16 inch), has an R-value of R-15.67. This is a lie. It violates the laws of physics.

    Don't send them your money.

  20. 2wXWDib2bj | | #21

    I live in your neck of the woods. You may be able to get used foam from a roofing company, one that does re-roofs on commercial, flat roof jobs. They ocassionally replace the underlying foam, as well as the membrane, apparently. There is a roofing company in Escanaba that sometimes has foam sheets for sale, Independent Roofing is the name. Some of these sheets may be tapered, though, this is how a "flat" roof gets the water to go to the roof drains.

  21. ginnis07 | | #22

    Hi Russel,
    Thanks!! Everyone has been very informative & helpful! We are actually going to the property tommorow!!

  22. EtnVbqm8De | | #23


    I own acerage in Chatham, SW of Munising, and want to build an A-Frame such as you are.
    Needless to say, your experience in this endeavor would be invaluable to me.

    I am also interested in establishing friendships in the area. I currently live on Lake St. Clair north of Detroit, and hope to be living in Chatham in a few years or less.

    I would love to meet you, and see your place sometime if you are open to it.

    David Colant
    A nice, family, peace, and God loving, unpretentious man age 49
    email at: [email protected]

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