Article #1486 - Vestibule Web-Based Training Questions and Answers

This article contains questions asked during the September 20, 2005 live broadcast of the Vestibule Web-Based Training session. The original language of the questions and answers has been modified to make them as generic as possible while retaining the applicable specific information.

I've seen many vestibules where both doors open at the same time. Doesn't this defeat the whole purpose of the vestibule? Is there anything in the IECC or Standard 90.1 that prohibits this?

Yes, it defeats the purpose of the vestibule because it eliminates the air lock effect that a vestibule would have on the entrance doors. Both the IECC and 90.1 have a requirement that you need to be able to enter and exit the vestibule without having both doors open at the same time.

Does the local law regulate which of these (IECC or ASHRAE) applies to a project, or is there some way to choose for a particular project which code is to be followed.

You pick the code you want to follow. The 2003 IECC gives you the option of either using 90.1-2001 or the envelope provisions of Chapter 8. Regardless of which you select, you must comply fully with all of the envelope provisions of the conditioned space or building.

On slide #16 of the presentation, are we required to have a vestibule on both doors or not?

Yes, you are required to have a vestibule on both primary entrance doors leading from the space if it is 3,000 sq. ft. or greater.

Are there any code requirements to prevent the owner from cutting power to the vestibule doors or fixing them in the open position?

No, there are no requirements preventing the owner from cutting power to the vestibule doors or fixing the doors in an open position after the owner receives the certificate of occupancy.

Is the 2003 IBC ventilation requirement also present in ASHRAE Standard 62.1?

For clarification, submit your question to: ashrae@ashrae.org

Slide #20 of the presentation states that the opening shall be not less than 8% but not less than 25 ft² but 15,000 ft² will require minimum opening of 120 ft² based on at least 8%. Therefore, this space may not require a vestibule, please clarify.

The 25 ft² is the minimum. So if the 8% of the floor area of the interior space exceeds 25 ft², then you would go with an opening of 8% of the floor area.

If you opt to take advantage of 90.1 to avoid vestibules, aren't you required to follow all of the 90.1 requirements for the envelope?

Yes, you must comply with the envelope requirements of 90.1 in its entirety.

If material handling (lumber storage area) communicates directly with the remainder of the store, and the material handling door is exempt, shouldn't there be a wall between the material handling area and remainder of store? Otherwise, not accomplishing much with vestibules at other end of the store.

The code does not require a wall between the material handling area and the remainder of the store. This would be a decision that the code official would need to make. Furthermore, not having a vestibule on these doors would increase the load in the space.

Using 90.1-2001, I assume all Wal-marts, Lowe's, Home Depots, and grocery super markets would be exempt from having a vestibule by virtue of being less than four stories. Is this correct?

Yes, using 90.1-2001 exempts buildings three stories or less from having a vestibule.

If unconditioned, how can the sprinkler system be protected from freezing?

You are allowed to put in a certain amount of space heating for freeze protection. By code, the space could only be conditioned to less than 50 degrees for it to be considered an unconditioned space.

Does the SHGC and U-factor glazing requirements apply to the interior side of the vestibule?

Not unless the interior wall requirements require you to have a low SHGC and/or U-factor.

Can you trade off a vestibule (i.e., performance approach)?

You cannot trade the vestibule off in the performance approach. (Per the 2003 IECC, Section 801.2 Application.)

Is every building required to have a vestibule regardless of where it's located?

There are certain parts of the country that are exempt from the vestibule requirement. In the IECC, climate zones 1-4 are exempt and in 90.1-2001 areas that have less than 1800 HDD are exempt.

If we use COMcheck, can we specify ASHRAE or IECC or does the software pick one and which one does it pick?

COMcheck has several code option choices. The user must select the appropriate code to show compliance to from the software's Code Menu.