Wall Assemblies for Maximum Efficiency: How Many Layers is Too Many?

Building professionals spend a lot of time dealing with production construction which has dialed in efficiencies and productivity to provide the maximum assembly for the cost per square foot.  The reality is in standard construction you build things in five or six layers. This is the standard in terms of building a wall system more efficiently and we have gotten it down to a science.  Generally a six layer home will give you a solid, energy efficient, comfortable home.
Occasionally, I work with builders on projects that remind me of possibilities beyond what is the status quo.  I recently had an opportunity to work with a builder who was building a custom home whose wall systems had 13 layers.  This wall had so much redundancy and robustness built into it that I just had to ask for a chance to visit the project and see this masterpiece being built.
This was the homeowner’s instruction: They wanted a thick wall, they wanted a silent wall, they wanted a highly efficient wall for them to own.  That’s one of the key’s to this discussion- the owner is focused on what comes afterwards- not what happened before. To achieve this goal the builder is employing a combination of traditional masonry materials and cutting edge products and systems.
In a similar fashion, a project that CertainTeed has been involved with at the Navy Yard in Philadelphia with Penn State achieves a similar goal but in a lighter and perhaps less massive assembly – to create a highly efficient wall system that can provide comfort, improve indoor air quality, better acoustics but, and here’s the rub- to still be affordable by more typical consumers.  This was done by using a 2 x 8 construction – providing a deeper wall cavity – A Blown-in-Blanket Insulation System, Weather Resistant Barrier, a Smart Vapor Retarder and Air Barrier System, a Wallboard Solution, Rigid Insulation on exterior and Insulated Vinyl Siding. This created an R30.5 exterior wall.
In both homes, products were used to address acoustics, indoor air quality and moisture control.  Do you need 13 layers?  Probably not but the pressure is certainly going to be on what layers remain to do more than they have in the past.