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Too many wall insulation options?

Bruce_Davis | Posted in Energy Efficiency and Durability on

Building a new home in Kansas City (DOE Zone 4A; mixed-humid {not too far from cold}). Summers are too hot and winters are too cold. Looking for the most cost effective and efficient method to insulate the exterior walls. Reading different books and forums, I’m having a hard time coming up with a comprehensive plan. My in initial thoughts were, starting from the inside:

2×6 studs, 24 OC. Uses less wood than 2×4 studs, 16 OC and reduces thermal bridging.

JM Climate Pro, Owens Corning ProPink L77, or similar formaldehyde free blown fiberglass wool. Supposedly only slightly more expensive than batts and much less expensive and better quality product than open or closed cell foam.


Foamboard (1″ ?) to reduce air infiltration and thermal bridging.

Rain Screen

Concrete stucco

Does a wrap (i.e., Tyvex) need to be added? I see on this site, the recommendation is no wall fill and just use 6″-10″ of foamboard. Is that the best idea? Does foamboard still need OSB for bracing strength? Can stucco go over foamboard?

Where does Zip fit in to all this? Their web site claims,

“Whether building to meet new energy codes or high-performance goals, ZIP System¯ R-sheathing streamlines water, air and thermal control. With built-in continuous exterior insulation and an integrated air- and water-resistive barrier, it eliminates the need for housewrap and additional exterior insulation in one, easy-to-install sheathing system. Find the right panel for your climate zone.”

It’s all a bit confusing. Thanks.

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  1. GBA Editor
    Martin Holladay | | #1

    Q. "Does a wrap (i.e., Tyvex) need to be added?"

    A. Building codes require walls to have a water-resistive barrier (WRB). If you want to have stucco, most experts suggest that you install at least two WRBs, not one. For more information, see these articles:

    "All About Water-Resistive Barriers"

    "To Install Stucco Right, Include an Air Gap"

    Q. "I see on this site, the recommendation is no wall fill and just use 6"-10" of foamboard. Is that the best idea?"

    A. It sounds as if you are describing the PERSIST method. (For more on the PERSIST method, see this article: "Getting Insulation Out of Your Walls and Ceilings.")

    Very few Climate Zone 4 builders use the PERSIST method, because Zone 4 is relatively mild, and the PERSIST approach is expensive.

    Q. "Does foamboard still need OSB for bracing strength?"

    A. Every wall needs a bracing plan. If you want to omit the OSB, you need to come up with an alternate method of bracing. For more information, see "Four Options for Shear Bracing Foam-Sheathed Walls."

    Q. "Can stucco go over foamboard?"

    A. Yes, but it's best to include a rainscreen gap, as noted in my article, "To Install Stucco Right, Include an Air Gap." You might also consider EIFS (a system that includes synthetic stucco installed on the exterior of a layer of continuous rigid foam). For more information on EIFS, see "Stucco and Synthetic Stucco."

    Q. Where does Zip fit in to all this?

    A. Zip sheathing is a type of OSB. For more information, see "Wall Sheathing Options."

    Zip R sheathing falls into a category I call "nailbase for walls." There are competitors. For an overview of the category, see "Nailbase Panels for Walls."

  2. walta100 | | #2

    First the answers to your questions depend on your goals, budget and your estimate of what future fuel costs will be.

    If this is a new home being built for speculation in the real-estate market will have very different answer than person building an off grid passive home they will own for the next 50 years.

    If you are trying to understand the financial cost vs energy use. The only tool I know of is a computer program paid for by the US government given at no charge to users called BEopt. To watch the training videos and model your first home will require about 40 hours of your time. This program can help you understand how the different walls performance over time considering your location ,fuel costs, interest rare, install cost.

    For my goals in central Missouri I built 2x6 16 on center filled with cellulose with Zip sheeting covered in 1 inch of foam topped with vinyl siding.

    Also to my way of thinking air sealing decisions are important than insulation choices.


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