December 7, 2012

Foam-Free Wall Assembly Guidelines by Climate Zone

Spanning eight climate zones, from very hot and humid to subarctic, and desert to rainforest,  the US presents widely varied demands on our building enclosures.    Anecdotally, there is much written on assemblies in cold climates but not so about hot climates.  And most of the literature today assumes foam will be the primary strategy for achieving a high performance.

But if you are no longer convinced that foam is the optimal strategy for making sustainable building or a sustainable environment (See, Foam Fails).   What then?  There is relatively little written in a comprehensive manner about high performance assemblies that are foam free in the US.   This blog is but one small attempt to help fill this general void of information – starting with wood construction wall assemblies.

Wherever your project might be, it would be nice to at least start with a set of suggested foam free assemblies that you can then customize to your particular project needs.   This is what these four steps attempt to do.

  1. Find your project location and climate zone on the US Climate Zone Map.  (NOTE: Climate Zones are on the move due to global warming – and may be appropriate to consider.)

    Climate Zone Map

  2. Find the group of assemblies suggested for that climate zone on the Foam Free Wall Enclosure Assembly Chart.

    Wall Assembly Chart

  3. Find descriptions of the basic control layers on the Control Layer Legend.

    Control Layer Chart

  4. Email us and/or phone us with questions.  Contact information is here.


    • Yes, these are by definition, oversimplifications.  It is up to the project professionals to develop the the complete details and specifications appropriate to the specific project, to ensure a robust assembly.
    • Micro-climates, orientation and shading need to be considered. Climate zones are generalizations and thus these charts and notes are solely meant as conceptual starting points for project specific details.
    • Find out why back-vented rainscreens are uniformly suggested, here.
    • Find our why service cavities are uniformly suggested, here.

Happy foam free building!


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5 Responses to Foam-Free Wall Assembly Guidelines by Climate Zone

  1. Paul Dowling December 8, 2012 at 9:46 pm #

    Thanks for a very helpful set of guidelines. Hopefully you can add a link to a Canadian climate zone map for your northern neighbours at some point.

  2. foursevenfive December 10, 2012 at 4:40 pm #

    Paul, you can use this map as a general reference –

    Zone A – being equal to US climate zone 4c

    Zone B – being equal to US climate zone 5

    Zone C – being equal to US climate zone 6

    Zone D – being equal to US climate zone 7 and 8*

    On the pacific shores it can locally be somewhat milder. This climate map of Alaska will give you an idea –

    And similar to the USA from west to east, after the rocky’s – it goes from dry to humid.

    And yes, we do ship to Canada. Airtight construction gets more and more important when it gets colder and colder – as well as having a vapor open exterior…

  3. Scott November 28, 2015 at 10:04 am #

    I just found your blog and I am enjoying it tremendously.

    The 475 blog post for vented rainscreen cladding…

    … references vapor open WRB layer behind the rainscreen cladding, stating: “they provide optimum drying potential of the enclosure when it is cold.”

    With this in mind, can you explain the logic for your chart recommendation to use DA as the “exterior air/vapor control layer” in climate zone 3A (mixed) – since DA is not vapor “open”?

    Note: As an architect of 22 years, it has taken some time for me to unlearn the hard rule of “place a vapor barrier on the warm side” in lieu of improved drying potential through “vapor open” assemblies. When the “warm side” is variable, I am normally inclined to specify vapor open materials in this position.

    • John November 30, 2015 at 3:12 pm #

      Glad to hear you are enjoying it, Scott. We aim to please.

      I believe the answer to your question is in our post here:

      Vapor variability on the interior will always be a benefit on the interior, regardless of the climate. But if we know that outside will nearly always be more humid than inside, that means the vapor drive is inward, and we can benefit from retarding that vapor drive on the exterior (hence using the vapor retarding, DA, or relying on sheathing to retard vapor). The same logic goes for crawlspaces under a building, where we know it will be humid most of the time. We also discuss these concepts a bit in our Sauna video:

      Let us know if that helps!
      When in doubt, we’d be happy to run a WUFI study to help determine which assemblies afford the greatest drying potential based on a specific location.

  4. Scott December 2, 2015 at 5:40 pm #

    Sensible! thanks.

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