I’ve dealt with some inconvenient exterior wall assemblies lately.
Although two recent projects had to comply with the 2012 International Energy Conservation Code, the nature of their exterior wall assemblies made achieving continuous insulation difficult in both projects, and made achieving a continuous air barrier difficult in one project. Energy calculations indicated that we did need continuous insulation on both; there was no getting around it.
In these projects, the insulation and air barriers were afterthoughts.
So the construction documents for both projects show some unusual applications of rigid insulation, and for one project, show an unusual application of an air barrier coating. It can all work, it can all meet the code requirements, but these situations may not be ideal for construction.
How did we get here? I believe that the exterior wall assemblies were dictated by the owner in one case and by the design-build contractor in the other case.
Owners and contractors aren’t required to be familiar with building codes. The person responsible for interpreting the building code and making sure that the construction documents comply with the code is the architect.
Whether the architect or someone else initially selects wall assemblies, the architect needs to verify code compliance, early in the project. And don’t forget that IECC! The earlier in the project that you take all code requirements into account, the more convenient for everyone, from architect to cost estimator to insulation installer.