“The desire to reach for the sky runs very deep in the human psyche” – César Pelli

As the world gets more dense and cities evolve, the need for space inevitably pushes a skyline higher. What began in Chicago in 1885 with the construction of a 42 m high (10 storey) tower has led us, over a century later, to the Burj Khalifa, standing at an impressive height of over 825 m high (over 154 storeys!). 

We recognize that these are obviously considered high buildings. But did you know that the Building Code takes a much more conservative stance and classifies what we may otherwise consider a low-rise building as a high building? Let’s examine this further. 

There is a common sense that the higher the building, the greater the risk. A risk to occupants evacuating a building as well as a risk to emergency workers who would be responding to an event. The higher the building, the longer each of these operations will take. It is necessary to also consider the use of the building and the demographics of its occupants in this analysis. Think of a long-term care facility, where the majority of occupants may require assistance with evacuation. By comparison, it will take longer to evacuate a building of this type, than a typical office building. 

The Building Code therefore incorporates additional protection measures to mitigate these risks; beginning with an assessment of the risk against the proposed use and building height. Specifically, Subsection 3.2.6. is used to determine whether a building is classified as a high building. 

When is a building classified as a high building?

Simply stated, residential, care and detention occupants are deemed more at risk (due to a potential for a delay in evacuation and/or emergency response) and consequently, have lower thresholds for high building classification. A building that has its highest occupied floor level more than 18 m above grade, in these circumstances, is considered a high building. The Building Code even takes this one step further for care occupancies by enforcing high building requirements for any care occupancy that is located above the 3rd storey. Remember that 154 storey Burj Khalifa? If built in Canada, it would have the same high building measures as a 4 storey long-term care facility!

Conversely, buildings containing assembly, business and personal services, retail or industrial occupancies are warranted a greater height of 36 m (for remaining classified as a low rise building), when measured to the floor level of the top occupied storey. However, there is a caveat to this allowance, where a larger occupant load is anticipated. This makes sense, as the more people you have in the building, the longer it will take to completely evacuate everyone. So, the Building Code will limit a low-rise building height to 18 m where the cumulative or total occupant load on or above any storey above grade, other than the first storey, divided by 1.8 times the width in metres of all exit stairs at that storey, exceeds 300. Sounds simple right? Let’s convert that to a more comprehensible graphic example:

This post is based on the National Building Code of Canada (NBCC). Please be mindful that other Building Codes may vary. For example, some differences are:

• The Vancouver Building By-Law Article 3.2.6.1. for application of high building requirements greatly varies from the NBC, and
• The Ontario Building Code includes a reference to retirement homes, mandating they be classified as a high building where the highest occupied storey is more than 18 m above grade.

So in summary, the 154 storey Burj Khalifa, a 4 storey long-term care facility and a 37 m high (approximately 12 storeys) storage garage, from a Building Code perspective, are each high buildings, and must be designed per the requirements of Subsection 3.2.6.

Now that we understand what constitutes a high building, let’s take a look at what this means.

How to protect a high building?

The Building Code requires that the following systems be incorporated into the design of a high building:

1. Limits to smoke movement,
2. Measures to protect connected buildings,
3. Emergency operation of elevators,
4. Elevators for firefighters,
5. Venting to aid firefighting,
6. Central alarm and control facilities (CACF rooms),
7. Voice Communication, and
8. Testing.

The intent of the above measures is to compensate for the increased time required for occupants to evacuate to a safe place and to provide sufficient time for emergency responders to perform their duties. 

Limits to smoke movement:

Although not common knowledge, between fire and smoke, smoke is often the more deadly. With a high building, there are more factors and/or systems that can influence the spread of smoke. Therefore, at a minimum, the Building Code requires a high building be designed: 

• to limit danger to occupants and firefighters from exposure to smoke,
• with smoke protection for floor areas and above-grade exit stairs,
• to limit smoke spread from below-grade levels to above-grade levels,
• to shut down non-emergency air-handling systems, and
• maintain make-up air fans serving public corridors in
• Group C residential occupancies.

Connected buildings:

When you have buildings of unequal height, stack effect comes into play. The concern with stack effect is the potential that smoke in one building could spread to the other building. This is because the pressure differentials between the two buildings could allow contaminated air from one building to migrate to the other building during a fire. 

To compensate for this, whenever a high building is connected to another building (regardless of the height of the other building), the Building Code requires that protective measures be incorporated into the design; however, the Building Code does not mandate a specific protective system. As per the Notes to the NBCC, the designer may wish to consider a large opening to the outdoors in the connection, so as to vent smoke. Alternatively, a mechanical system can be installed to maintain a higher pressurization within the vestibule connection. 

It is important to note that even if you are constructing a new low-rise building, that is intended to be connected to an existing high building, then the above protective measures will be required. 

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Emergency operation of elevators:

Neat fact: the invention of the elevator was the reason that buildings were able to get taller! Can you imagine climbing 154 storeys worth of stairs? Or, can you imagine the stamina required for emergency personnel (fully encumbered with all their gear) to climb the stairs of a high building? 

So elevators are great for reaching those upper storeys, but we have to ensure that they are available and operational for emergency personnel during an emergency. Therefore, the Building Code requires all elevators to be designed with an emergency recall system that is manually activated by key-operated switches. Additionally, each elevator cab is required to be equipped with in-car emergency service switches in order to notify operational personnel in case of an emergency.

Elevators for firefighters:

As stated above, there is a necessity to ensure that elevators remain operational and available for use by emergency personnel. But further to this, each building must be equipped with at least one elevator, designated exclusively for firefighters. These elevators will have additional requirements beyond those stated previously:

• Minimum dimensional sizes (not less than 2.2 m²), capable of carrying a load of 900 kg to the top floor that it serves, within 1 minute,
• Protection of the elevator shaft openings, either through closures and interlocks, a 45 minute fire-rated vestibule or a 1 h fire-rated corridor system,
• Must serve all floor levels above grade, however the Building Code permits a single elevator change where a single elevator shaft does not serve all floor levels of a building, and
• Protection of electrical conductors that serve the firefighters elevator.

Venting to aid firefighting:

In order to reduce the amount of smoke that may accumulate in a high building, a means of venting each floor area to the outdoors is required. Ideally, the provision of operable windows, wall panels, smoke shafts or the building exhaust system should be used for this purpose. Where operable windows are the selected venting system, they must be identified with permanent markings to assist firefighters in locating vent windows in a fire situation.

Fixed glass windows are prohibited from being used for smoke venting purposes, unless it can be shown that precautionary measures have been taken to protect persons below from falling glass. Additionally, the Building Code does not permit elevator hoistways to be used for smoke venting. 

Central alarm and control facilities (CACF rooms):

All high buildings require a CACF room, to assist with fire emergency response operations. These rooms must be located in the vicinity of the principal entrance to the building and must include the following:

• Means to control voice communication systems,
• Means to indicate alert / alarm signals both audibly and visually, including signal silencing and actuation switches, 
• Visual indicators of elevator emergency recalls, 
• An annunciator,
• Means to transmit alert / alarm signals to the fire department,
• Door hold-open device releases,
• Means to actuate auxiliary equipment (e.g., smoke control, pressurization systems and smoke venting), 
• Communication with in-car elevator telephones, where elevators (not firefighter elevators) are equipped with telephones, and
• Means to visually indicate sprinkler system waterflow signals, with audible and visual indications of sprinkler and standpipe system supervisory and trouble signals, inclusive of system silencing visuals.

Voice Communication: 

The requirements for a voice communication system are not enforced for every high building. Conversely, the Building Code indicates specific circumstances where a voice communication system is required. This is typically as a result of a higher occupant load, but is also required for any building where the floor of the top storey is more than 36 m above grade. A voice control system is also required for any care occupancy that is located above the 3rd storey. 

Therefore, if you were to have a residential building that has its highest occupied floor at 19 m above grade, although classified as a high building, it would not require a voice communication system (assuming there are less than 1 000 people in the building).  

Testing:

Rarely (thankfully!), these fire and life safety systems (e.g., smoke control, pressurization systems and smoke venting) are actuated. Therefore, without consistent testing, the operability of these systems cannot be ensured. On this basis, as with any fire and life safety system, testing must be undertaken to ensure that these systems will operate as originally designed and installed. 

By incorporating the above additional protection measures, we can enable safer, higher buildings, whether they be 4 storeys tall or 154 storeys tall.  

As always, be sure to check your local Building Code for differing requirements. 

Want to Dive Deeper?

A Precision course on High Buildings, instructed by Megan will be available mid-March in the Kilo Lima Code School. Subscribe to updates on upcoming courses here to stay in the loop!