Many designers and specifiers understand controlling air, vapor, and thermal transfer helps mitigate moisture problems within the building envelope. Moisture accumulation is a performance adversary that can lead to structural deterioration, finish damage, organic growth, and reduced building longevity.
At this point, most design/construction professionals have a pretty good understanding of the need for well-designed air and moisture control layers in wall assemblies. Water-resistive barriers (WRBs) have been in use for decades; in more recent years, a number of new systems have popped up that combine these products with an air barrier function.
Initially, water vapor diffusion was seen as the likely culprit for condensation problems; designers and consultants spent hours running and analyzing wall assemblies using the dewpoint method. With such analyses came the concept the wall system should be tuned for maximum condensation resistance by altering or selecting the appropriate permeability of the wall components. However, to create a truly robust wall system with the greatest condensation resistance and drying potential, designers need to look at altering the temperature profile of the wall assembly by moving insulation as far as possible to the exterior of the wall.
When properly applied, tests can yield valuable insight into the installed performance of systems, aid investigators in determining the cause of a failure, or help to determine if a product is performing to its intended level. However, when improperly applied, many tests and standards can produce misleading results, improper conclusions, and lead to unnecessary repairs or remediation efforts. Within this context, the article takes an in-depth look at roofing assemblies, along with glazing, masonry, and air barrier assemblies.
This article describes the air barrier performance requirements for the desired wind load design specifications. The performance level is not determined by the type of air barrier material, but by the installation details. Examples of how these details can impact the performance level for a given air barrier system are provided, with special emphasis on mechanically fastened air barriers.