The Brave New World of Insulating Wall Assemblies

A proprietary wall system marketed in Germany which utilizes 60-80mm reed insulation as the exterior insulation material.

The effective date for the 2013 California Title 24 Building Energy Efficiency Standards (a.k.a. California Energy Code) will be July 1st, 2014. This update requires single-family residential buildings to be 25 percent, multi-family to be 14 percent and non-residential buildings to be 30 percent more energy efficient than the previous 2008 standard.

Under the prescriptive method, new requirements for the residential building envelope entail increasing the cavity insulation value from R-13 to R-15. Additionally, an additional layer of minimum R-4 rigid insulation will need to be applied outboard of the wall cavity.

It should be noted that these requirements apply under the prescriptive method. Equivalent wall assemblies can be supported if they “pencil” out according to the building’s energy modeling analysis.

That said, the addition of rigid insulation does vastly improve the performance of the wall assembly, and by 2016, will become a mandatory feature. So it’s best to understand the ramifications of so doing.

Diagram illustrating structural considerations of attaching finish material through exterior insulation (courtesy Siegel+Strain Architects, Emeryville).

These considerations include: 1). selection of the appropriate rigid insulation, 2). method of attachment of the rigid material to the structural sheathing, 3). attentiveness to position of the dew point within the assembly and, 4). method of attachment of the finish material to the rigid insulation.

The standard wall assembly currently in use has benefited from generations of trial and error to perfect. The addition of rigid insulation to the assembly is in its relative infancy.

Thus, as yet there is no standardized approach guaranteed to perform reliably in the long term i.e. over the life of the building not experience any of the failure modes implied by the four considerations listed.

Implied potential failure modes include:
1). inappropriate rigid insulation: deterioration or delamination.
2). ill-considered insulation attachment: separation from substrate.
3). ignorance of dew point: liquid water within wall system.
4). ill-considered finish attachment: detachment or failure of finish material.

The prudent builder or designer striding bravely into the brave new world of rigid insulation will do well to research quite carefully the appropriate wall assembly solution, one that performs as intended while avoiding the potential pitfalls inherent in the assembly.

On March 19th, 2014 at ADPSR’s Better Envelope Solutions Showcase in San Francisco, architect Larry Strain presented a talk entitled, “Insulating Exterior Assemblies”. In it, he discussed in detail the nature of these concerns, options with respect to “green” insulation options in the assembly, together with an example of practical application in a realized project. The link is at: Insulating Exterior Assemblies.

2 thoughts on “The Brave New World of Insulating Wall Assemblies

  1. Bob Theis

    Daniel, Ages ago I was reassuring you that petrochemical rigid insulation was a placeholder, and biocompatible ones were coming. I thought of that conversation when I saw this clip about wood based foam:

    Relatedly, Tracy Thieriot and I did a great retrofit last year “upholstering” a stud and plywood box with 2 layers of 1-1/2″ thick, 9 lb mineral wool batts covered with nylon netting, which we then earth plastered. Not only more ( and exterior ) insulation, but fireproofing, plus we could round the corners and soften up the box.


    1. santacruzarchitect Post author

      Hi Bob, I honestly cannot for the life of me recall the exchange. Could it have been as participants on the CASBA ProCourse Panel? At any rate, what we both were pushing for is coming to pass. Glacially, of course 😉



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