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Recommendations for finishing a house on island in SE Alaska?

user-1119955 | Posted in GBA Pro Help on

I purchased a partially completed house on a small island 80 miles south of Juneau. The 40×30, 2.5 story house is built on pilings with 2×12 floor joist on 16″ centers, 1×6 walls, 16″ oc, a combination of 5/16th osb and plywood, wall sheeting, all windows and doors installed, a finished raised seam metal roof, second floor (2×12, 16″oc and stairway done, and minimal inside framing accomplished. The amount of framing in the house shell is really overdone!
The climate is “temperate rainforest” (lots of rain), with the record low temperature of -6 F and average January temperatures of 23.5 F. Tyvek on the outside is mostly weathered and blown away.
All building supplies must be ferried to a nearby village, off loaded, then reloaded on a small boat before being floated across a channel and then transported to the other side of the island; making all supplies very labor intensive and expensive (not complaining just being factual).
I want to finish this house and most likely will live there 4 -5 months yearly (May through September), although I may spent a couple of winters as well.
My main questions deal with how best to insulate, foam exterior sheets + wall batts, just batts, just exterior foam and how many inches. I plan on a metal and wood siding on a rain screen, although some vinyl siding is an option.
I hope my description elicits some suggestions from the experts, I’m not a builder, although I worked in the construction trades a lifetime ago and have some diy skills.
I would appreciate any and all help.


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  1. GBA Editor
    Martin Holladay | | #1

    You wrote, "The amount of framing in the house shell is really overdone!" If so, one of your descriptions confuses me: you wrote that the house has "1x6 walls." Are you describing the studs or the sheathing? If you are describing the studs, they are unusual. (Perhaps you meant to write "2x6.")

    Q. "My main questions deal with how best to insulate: foam exterior sheets + wall batts, just batts, or just exterior foam, and how many inches."

    A. Of the three possibilities you listed, "just batts" would be the worst, and "just exterior foam" would be the best. You are in Climate Zone 7; according to the 2009 International Residential Code, you need a minimum of R-21 of wall insulation. If you decide to use just rigid foam, that means that you need about 5 inches of EPS, or about 4.5 inches of XPS, or about 4 inches of polyisocyanurate.

    For more information on this topic, see:

    Getting Insulation Out of Your Walls and Ceilings

    How to Install Rigid Foam Sheathing

    Calculating the Minimum Thickness of Rigid Foam Sheathing

  2. davidmeiland | | #2

    If all windows and doors are installed, doesn't that reduce the options? I've not done "innie" window installations, so maybe not.

  3. user-1119955 | | #3

    Martin, sorry I did mean 2x6 for wall studs. Also, would you suggest house wrap with the exterior foam? If so, under or over the foam?

  4. GBA Editor
    Martin Holladay | | #4

    Q. "Also, would you suggest housewrap with the exterior foam? If so, under or over the foam?"

    A. If you read the article I linked to -- How to Install Rigid Foam Sheathing -- I think that you'll find that the article answers most installation questions, or provides links to articles with more information.

    One of the links found in that article is this one: Where Does the Housewrap Go?

  5. mackstann | | #5

    If the windows are already installed and you don't want to re-frame them with plywood extension boxes, then you will be doing an "innie" window detail and the housewrap will need to be under the foam. A crinkled housewrap like Tyvek Drainwrap is a great option when foam is going to be attached over the housewrap -- it will make it easier for any moisture behind the foam to drain out.

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