Vestibules in 90.1

As I recall ASHRE offers an alternate compliance method, in that under certain conditions the HVAC system can be designed to not require vestibules. Discuss this with your MEP engineer. There are also requirements in some codes that rooms over a certain size (that have exterior entrances) have vestibules. Also, we have been successful in using vestibules at main entrys and exits and not at all exterior doors. This includes non-exit only doors that are only expected occasional use. The pattern catches 95%+ of the occupants and visitors and to date no problems with the reviewers.

ASHRAE has a clarification to the vestibule question at this link: http://www.ashrae.org/technology/page/2053 It is from 90.1-1999, but the exception verbiage is still the same. Background: Section 5.2.3.4 requires enclosed vestibules for doors that separate conditioned space from the exterior. Several exceptions to Section 5.2.3.4 are given. Exception C states that “Doors not intended to be used as a building entrance door” are not required to have a vestibule. Interpretation: A door that is not a main public entrance to the building is not required to have a vestibule. A controlled access door that opens to a patio which does not have egress from the building’s exterior would not be considered a building entrance door and therefore would not require a vestibule. Note that iECC-2009 (502.4) also has requirements (with some exceptions) for vestibules.

Can the vestibule be a small conditioned space? Regards

This requirement for vestibules will cause a lot of issues for retailers who love to keep their doors open all day long to their showrooms which are often well over 3,000 SF. Is it landlord's responsibility or the tenants responsibility to install the vestibule to meet the requirement?

Depends on what kind of code or standard and jurisdiction you are asking about.