Which Wall and Roof Insulation to use?

MTguySeptember 20, 2013

I've already accepted a floor plan and my footings are in, but I would like to know what wall system I should be using. My bid was for 2x6 walls, 16" on center with 1/2" osb sheeting and vinyl siding. The insulation was to be R19 Batts (I'll at a minimum upgrade to R21) with a vapor barrier on the outside of the home and sheetrock on the inside. I'm wondering if I go with a 3/4" or 1" foam with taped seams under the vinyl siding but on top of the OSB sheeting, R21 Batts and a smart vapor barrier under the sheetrock if I will meet code and second if it is worth the extra couple thousand it will cost me. For reference, I am in North Dakota at the edge of zone 6 and am doing a geothermal HVAC system.

I will have vaulted ceilings so I have no idea how that will be done but am interested in finding out what I can do to help there as well.

Finally, I'm building on a full basement (6' to grade). I wont have anything under the slab, but is it worth it to put an inch of foam outside the slab? I would like to match it up to the upstairs for width.

Just for reference, my floorplan is already accepted as well as the bid, but I think this could be a worthwhile upgrade, particularly if I do the foam myself.

If you need more information about my project to make an informed decision I've put a link to my build log below.

Here is a link that might be useful: www.ultimatehomestead.com

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Have you thought about going with ICF?

    Bookmark   September 20, 2013 at 10:03PM
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It was cost prohibitive here. I am locked into 2x6 construction at this point.

    Bookmark   September 20, 2013 at 11:01PM
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Upgrading to IECC 2012 will payback in 4.6 years while providing a more comfortable indoor environment than minimal insulation.

For the vaulted ceiling, there are a number of sound approaches.

This post was edited by worthy on Mon, Sep 23, 13 at 10:23

    Bookmark   September 20, 2013 at 11:07PM
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the more you spend right now on sealing and insulating, the more you will save over the life of the home. In your climate (same as mine) air sealing and then insulating is very important. Yes, do the exterior foam. 1" is infact on the low side, and if you can increase it to at least 1.5 thats better. Labor to install is the same, so just slightly more material cost.
Obviously everyone is on a budget, but I stress to tweak it and get the guts and bones of the house done right, as you can not easily change it. If you need to lower certain finishes to achieve it, that is much better money spent. See what you can do for getting sub slab insulation. if you ever plan on having family or bedroom space in the basement, sub slab insulation is money well spent. 2" under the slab is typcially the normal around here for high performing houses.

    Bookmark   September 23, 2013 at 9:30AM
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