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Help with old building in Michigan

acmmd2003 | Posted in Energy Efficiency and Durability on

I’m looking for some advice on how to properly sheathe and insulate exterior walls on an old commercial building. The property is in Ludington, Michigan (Zone 6) and right now (from the inside out) there are 1” pine boards, actual 2”x4” studs on 16” centers, no insulation, and old cedar clapboard siding.

My plan is to remove the exterior siding and hang Huber ZipWall or perhaps InSoFast 2.5. Once the sheathing has been installed, I’m thinking about removing the interior pine boards, scabbing 2x2s on the inside of the old 2x4s, and filling the stud cavities (now 5 1/2” deep) with batt insulation, then hanging drywall.

I’ve read conflicting reports about whether the ZipWall will work in Zone 6, and frankly, I’m not that sure about any of this. I’ve read just enough Fine Homebuilding and to be dangerous, but I’m not a pro builder. The local contractors are scratching their heads over this as well.


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  1. user-2310254 | | #1

    How do you plan to use the buildings? Still commercial? Will it have heat and air?

  2. acmmd2003 | | #2

    It's a two-story building. Upstairs will be two apartments and downstairs will most likely be retail or offices. Planning on separate HVAC for all units. 2400 square feet each floor.

  3. GBA Editor
    Martin Holladay | | #3

    The basic rules for this type of wall are explained in this article: Calculating the Minimum Thickness of Rigid Foam Sheathing.

    You're going to end up with the equivalent of 2x6 studs. If you want to install rigid foam on the exterior side of 2x6 walls in Climate Zone 6, then the rigid foam needs a minimum R-value of R-11.25.

    InSoFast 2.5 panels are rated at R-10 -- not quite enough. You could either beef up the rigid insulation with another layer of rigid foam (ideally, installed with staggered seams), or you could choose a different product with a higher R-value.

    I'm not sure what your question is concerning Zip sheathing. If you are talking about Zip sheathing without any foam layer -- not the Zip R product -- of course you can use it. If you want to install Zip R sheathing (without the InSoFast foam), you would need to select the 2 1/2 inch thick product that Huber now offers (7/16 inch thick Zip panel plus 2 inch thick foam with a combined R-value of R-12.6). For more on this option, see this article: Nailbase Panels for Walls.

  4. Expert Member

    The decisions about HVAC, wall and ceiling assemblies, use of combustible materials, locations of openings and services, etc, will all be dominated by the demands for fire separation between the commercial and residential occupancies. In most jurisdictions these have to be made in consultation with an architect or engineer. That's where I would start. Once you have those requirements met you can then decide what works from an energy conservation perspective.

  5. acmmd2003 | | #5

    Thanks, Martin - Your answer helps a lot. I did read the article about calculating the thickness of rigid foam, BTW. I just didn't put it all together for this application. I also didn't know that Zip R (that's what I was referring to in the first place - not the standard Zip system) went out to R-12.6. I will use that.

    As to Malcolm's comments about the architect, I do indeed have an architect working on this, but neither he nor I had clarity on the Zip R sheathing capabilities, and I'm pretty sure that he's not up on the InSoFAst product. But now we both are, so thanks, all. Your answers point us in the right direction.

  6. Expert Member

    i didn't mean to sidetrack you, just hoped you had that thought through. Glad you got the answers you needed. Good luck with your project.

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