Involve an experienced blower-door testing agent in visual inspections before drywall is installed in any of the units. This will ensure that problem areas are addressed while they are still easily accessible. Also bring the blower-door expert in for early testing, once the drywall is installed, but before painting, finish materials, and appliances are installed. This will point out penetrations that need to be sealed between units and allow contractors to address those penetrations in the remaining units to ensure that all units meet the standard.