Evaluating the Long-term Performance of Air Barrier Systems in Modern Buildings

The durability of air barrier systems is a topic that is rarely discussed during the design phase of most projects. An unfortunate amount of effort is spent on drawing details and specifying products with the sole intention of meeting energy code requirements, with much less thought being given to how those systems actually will be constructed and possibly worse – how those systems will fare over time.   
Air barrier systems are very complex and involve a wide variety of components.  Windows, doors, walls, foundations, and roofs all need to work together, since even small breaches in the building air barrier can significantly reduce performance.  But with so many different systems, all of which are composed of different types of materials, the risk of both physical and chemical incompatibilities between air barrier materials or poor weatherability is high.  Unfortunately, many of these problems only will manifest after construction of the building is complete.  The point of failure is likely to go unnoticed, as membranes lose adhesion, sealants fail, or expanding foam shrinks away from its substrate within walls that are concealed by interior finishes and exterior cladding or at small joints or concealed in assemblies.   
This paper reviews previous research related to the long-term durability of air barrier systems, focusing on wall membranes and fenestration systems.  It also discusses energy modelling of a typical large building at varied air leakage rates to show the associated potential impacts to building energy use.  These results show that, as an industry, current energy code requirements are both reasonable and achievable with modern materials and industry knowledge. Instead of energy losses, deterioration of the building materials due to a poorly performing air barrier may be of greater concern.