Stair/elevator shaft pressurization and the National Building Code of Canada

[WinniPEng]

Hello, I'm trying to resolve what I read as the NBCC requirements, and what I keep seeing done in practice for new high-rise buildings with respect to stair and elevator shaft pressurization systems. I am in the midst of designing the HVAC systems for a new 10-storey apartment, and want to be sure I have correctly understood the code, section 3.2.6 in particular. Based on what I'm seeing other engineering firms doing, it would appear that they are either reading a code that I am not aware of, or they are interpreting the NBCC differently than I am. Any requests for assistance from the local code officials to ensure I have understood the requirements properly have gone nowhere.

My understanding of the code requirements (including the explanatory info in the Appendix) for "high buildings" as designated by the code can be summarized as follows:
1. Stairways for the below-grade level(s) and those for above-grade levels must be kept separate from each other.
2. stairways serving floors below-grade are to be pressurized with 1000 CFM per storey served during a fire alarm, with the air introduced at the bottom, and relieved via the exit door at grade level.
3. Stairways serving floors above-grade are to lead to an exit door directly to outside, which shall have a hold-open device to hold the exit door (or doors if there's a vestibule) open during a fire alarm, and will rely on the stack effect to create positive pressure in the stair shaft.
4. Any fans in the building serving 2 or more storeys shall be able to be stopped at the central alarm panel with a manual switch.

This all appears to be pretty simple stuff, but I continually see designs being installed (I work closely with a large mechanical contractor) that include several-thousand-CFM fans that will pressurize the above-grade stair and elevator shafts (with roof-top mounted fans) during a fire alarm. There is no mention of this being required in the NBCC, so where might they be getting the idea that this is something that needs to be done? Can anyone explain to me if I'm missing something? Also, these fans are not equipped with any means of heating this air... would there not be any danger of freezing either the sprinkler main (often located in the stair shaft) or any water from sprinkler heads that have gone off, and made its way towards the stairwell door that people are exiting from?

Thanks!

 

[KiwiMace]

Your code reqt number 3 seems pretty unique to me. I have done this in a couple of countries and the code typically includes the following:

Control the pressure in the above ground stairwell at 50Pa with the doors shut.
Maintain 1m/s avg air velocity with two doors open.
Doors must self-close, and open with no more than xx N of force.