The subhead to this article—Whether you follow your local building code or shoot for high performance, use this guide to make sure your walls won’t fail—makes a promise it can only partially keep. The information you’ll find here can help you design a wall that will perform well in theory, but installation details are equally, if not more important.
Most catastrophic wall failures are the result of one thing: water getting into the assemblies and not being able to dry. Despite their name, the presence of water-resistive barriers (WRBs) isn’t enough. WRBs must be installed impeccably and integrated properly with flashings, and even then, they are known to fail when water can’t drain or dry. That’s why most of the wall assemblies you are about to see incorporate rainscreen siding details that most homes with most siding types in most climates can benefit from, though there are exceptions.
Similarly, walls can fail to perform when the air barrier is not designed and installed to be continuous from one plane of a building to the next. A leaky house is not only inefficient and uncomfortable, it is air infiltration and not vapor drive that causes most condensation issues in walls.
Walls also can fail when not enough insulation is installed or when it is installed poorly. While this failure is often about efficiency and comfort, in some of the assemblies you’ll see below, insulation is used to reduce the likelihood of condensation by controlling the dew point temperature at potential condensing surfaces. Therefore, a failure in this case can also lead to rot and mold issues.
Finally, walls can fail when vapor retarders are used improperly. This failure is not typically the result of poor installation, but rather the result of using a…