Category Archives: Building Envelope

Vestibule Requirement

I just got off the phone with Greg McCall. He is an energy policy specialist with the City of Vancouver. We were discussing the vestibule requirements of section in 2010 and addendum dm that changed the requirements for the 2013 standard.

As I travel around the country, I find that the wording of the exceptions to the vestibule requirements cause some trouble. Exception “e” excludes doors from having vestibules. The wording changed in 2013 in this way. “Building entrances in buildings that are: located in climate zone 3, that are less than four stories above grade, and less than 10,000 ft2 in gross conditioned floor area.” The words underlined were added and crossed out removed. The italics represent a word that is defined in the Standard; in this case, gross conditioned floor area, which can be found in section 3 of the standard under floor area.

Climate zone 3 is cooling dominated. This exception has a sister requirement, f, for more northern climate zones. “Building entrances in buildings that are: located in climate zone 4, 5, 6, 7, or 8 and that are less than 1,000 ft2 in gross conditioned floor area.” When I traveled to these climate zones, places such as Alaska, I was told that the 1,000 ft2 referred to the area for the entrance not the building. The changes in language are supposed to make it clear that it is the building that is less than 1,000 ft2. If you look at the definition of gross conditioned floor it certainly does make it clear. Greg is not so certain that the new wording will be understood. Many designers in northern climates have interpreted this to mean the door area has to be more than 1,000 ft2 before a vestibule is needed.

He also has a problem with exception g. “Doors that open directly from a space that is less than 3,000 ft2 in gross conditioned floor area and is separate from the building entrance.” This exception is for tenant spaces that might be on the ground floor of a large office building or hotel and open to the street. If these tenant spaces are less than 3,000 ft2 they do not need a vestibule. His question is , why do freestanding stores of 1,000 ft2 need a vestibule when these tenant spaces do not? Canadians like consistency.

Another change from the 2010 standard is for large buildings with entrance levels of greater than 40,000 ft2. The vestibules of these buildings, when the doors are self-closing, must have a travel distance between doors of 16 ft or more. The total area of a vestibule must be less than “50 ft2 or 2% of the gross conditioned floor area for that level of the building.”

Anytime you use 90.1, you need to check the definitions. As long as you understand what gross conditioned floor means, you can know that the exceptions are referring to the building and where you should put the vestibules. If you want to build the building in Vancouver, Greg can help you.

Opinions expressed here are solely my own and do not express the views or opinions of ASHRAE or the 90.1 committee.