Section 5.4.3.4 of ASHRAE 90.1-2010 requires enclosed vestibules at building entrances ("Building entrances that separate conditioned space from the exterior shall be protected with an enclosed vestibule"). I would like to ask if anyone heard of an exception from this rule. Our project consists of a renovation of a historic building so the inclusion of a vestibule is very problematic. None of the exceptiones described in ASHRAE applies. Local authorities don't allow to use revolving doors in this project and implementation of a vestibule is very hard because of a few interor stears which are very close to the exterior entrance. However the design team decided to provide an air curtain above the entrance. Does anyone know if in that case it is possible not to comply with ASHRAE Section 5.4.3.4 requirements?