Which defect might be caused by improper overlap of air barrier materials?

The defect caused by improper overlap of air barrier materials is primarily an un-adhered membrane. This issue occurs when the edges of air barrier materials are not adequately overlapped or sealed, preventing them from adhering properly to each other. When there's insufficient overlap, the bonding between adjacent sections of the membrane can be compromised, leading to gaps that allow air infiltration. This not only defeats the purpose of the air barrier, which is to prevent uncontrolled airflow, but can also lead to a variety of performance issues in the building envelope. Un-adhered membranes are particularly problematic because they can result in further deterioration of the material, and potentially diminish the overall effectiveness of the air barrier system.

Other defects, while they may arise in different contexts, do not directly relate to the overlap of materials in the same way. For example, unsupported bridging refers to features that are not properly supported, surface bubbling can result from moisture or air trapped during application, and heat loss is a result of air leaks which can stem from issues like those found in an un-adhered membrane, but is more of a consequence rather than a direct defect due to improper overlap.