Stair Pressurization Design: Code, Airflow and Testing in Canada

Stair pressurization design is the engineering of a dedicated supply fan, its air path and its controls so that an exit stair stays at a higher pressure than the adjacent floors during a fire, which discourages smoke from entering the escape route. In Canada the requirement originates in the National Building Code and its provincial adaptations, such as the Ontario Building Code, and the design itself rests on leakage assumptions, door forces and building stack effect that must be verified on site.

TL;DR

• A stair pressurization system supplies outdoor air to the stair shaft so that air leaks outward through door gaps and cracks, rather than smoke leaking inward.
• Design airflow is governed by two competing limits: enough pressure to resist smoke, and a door-opening force low enough for all occupants to use the stair.
• Code obligations depend on the province and the code edition adopted there, so Ontario and Alberta projects must be checked against their own adopted codes, not a national model alone.
• Design assumptions about leakage rarely match the as-built building, which makes commissioning tests essential and periodic retesting a normal part of ownership.
• Early coordination between the mechanical, electrical and fire protection disciplines prevents most permit delays.

Table of Contents

• How stairwell pressurization works
• Which Canadian code provisions apply
• The design basis: pressure, airflow and door force
• Equipment, controls and emergency power
• Conditions that affect performance
• Testing and commissioning
• Our perspective
• How FutureGen supports stair pressurization projects
• FAQ
• Sources

How stairwell pressurization works

A pressurized stair is a controlled leak in the right direction. A fan supplies outdoor air to the stair shaft, which raises the pressure in the shaft above that of the adjacent floor spaces. Because air moves from higher to lower pressure, it flows outward through door clearances and construction cracks, and smoke is discouraged from entering. The Canadian National Research Council describes this principle in its air leakage data for elevator and stair shaft design: the supply fan injects outdoor air so that the shaft pressure exceeds that of the floor, limiting smoke migration into the stair.

The supplied air has a second function. It can dilute smoke that entered the stair before activation or while a door was open. The overall objective is to keep the stair tenable for longer, both for occupants evacuating and for firefighters using the stair for access.

The U.S. National Institute of Standards and Technology frames the same approach as smoke control by mechanically inducing pressure differences across barriers, normally holding the stairwell at a higher pressure than the spaces beside it. Its analysis guidance lists wall and door leakage, the number and location of injection fans, and stair compartmentation as the factors the designer must account for.

Which Canadian code provisions apply

The National Building Code of Canada is a model code. The Canadian Board for Harmonized Construction Codes states that national model codes take effect only when a provincial or territorial authority adopts them, in whole or in part, and that these authorities are responsible for adoption and enforcement. A stair pressurization requirement is therefore always read through the code edition and amendments in force in the province where the building is permitted.

In Ontario, the Ontario Building Code addresses smoke movement in high buildings through Article 3.2.6.2 and the Ministry’s Supplementary Standard SB-4, “Measures for Fire Safety in High Buildings”. The published text of the Ontario Building Code provision on limits to smoke movement requires a sprinklered building within its scope to be designed in accordance with SB-4 so as to limit the danger to occupants and firefighters from smoke. It also sets performance expectations for exit stairs serving storeys below the lowest exit level, and requires a vent to the outdoors at or near the bottom of stairways serving storeys above that level. The provision should always be confirmed against the edition current at the time of the building permit application.

In Alberta, the applicable framework is the Alberta edition of the National Building Code and the Alberta Fire Code, adopted by provincial regulation. Designers should confirm the edition and any provincial amendments before fixing the design basis. Other provinces move at their own pace: British Columbia, for example, announced in 2024 that new single-egress-stair buildings permitted up to six storeys would require safety measures including sprinklers, smoke-management systems and wider stairs. That is a British Columbia rule and does not apply in Ontario or Alberta, but it shows how provincial requirements for stair smoke management can diverge from one another.

Two practical points follow for owners and developers:

1. Establish early whether the building falls within the high-building provisions, since this determines whether a pressurization or alternative smoke-limiting measure is part of the permit scope.
2. Keep the fire protection engineer, the mechanical designer and the electrical designer working from the same code edition from the start of schematic design.

Our fire and life safety design practice handles this coordination for Ontario projects, and our guide to life safety systems in Alberta covers the compliance and maintenance context there.

The design basis: pressure, airflow and door force

Stair pressurization design balances two constraints that pull in opposite directions. Too little pressure allows smoke to infiltrate the stair, while too much pressure makes the stair doors difficult to open. The NRC’s review of stair pressurization systems for smoke control identifies precisely this tension and lists the commonly used remedies.

Minimum and maximum pressure differentials

The explanatory Appendix B to the 2007 British Columbia Building Code, which reproduces National Building Code guidance, offers helpful reference figures. It recommends a minimum pressure differential of 12 Pa for mechanical stair pressurization in a sprinklered building, where stack effect may dominate smoke movement. It does not set one universal maximum differential. It notes that research suggests 130 N as a force most people can overcome at a door, while 90 N is generally specified in the Code. Because every pascal across a door adds to the force required to open it, the maximum differential is derived from the door width, hardware and closer force of the particular project, rather than adopted as a fixed number.

What the airflow calculation includes

The supply airflow is determined by the leakage paths the air must pass through, plus the airflow required to maintain protection when doors are open. A defensible calculation typically accounts for:

• the leakage area of stair doors and their clearances, wall construction, and shaft penetrations;
• the number of storeys and the height of the shaft, which control stack effect in cold weather;
• the design outdoor temperature and the resulting buoyancy pressure;
• the number of doors assumed open at once, typically the discharge door and the fire floor door;
• the location and number of supply injection points;
• the pressure relief path, whether by dampers, exit door relief or building leakage.

The NRC’s 1977 publication on measures for fire safety in high buildings stresses that successful application requires an understanding of smoke movement and building characteristics, and that a realistic assessment of enclosure leakage is critical. This is why we do not size the fan from a rule of thumb. Leakage assumptions need to be tied to the actual construction type, door types and gasketing specified in the drawings.

Open doors and over-pressure

The NRC identifies stair doors as a critical design issue: opening a door causes intermittent loss of effective pressurization, so the fan needs sufficient capacity to resist smoke entry in door-open conditions. The same body of work describes the usual measures that keep the closed-door case from over-pressurizing the stair:

• pressure-relief dampers, including barometric types;
• feedback control of the supply, with fan bypass;
• variable-speed or variable-pitch fans;
• relief through exit doors;
• multiple injection points along the shaft to even out pressure over the height.

The choice among them depends on stair height, the control strategy and project cost. In tall stairs, a single injection point at the base tends to produce large pressure differences between lower and upper floors, which is one reason multiple injection points are common.

Equipment, controls and emergency power

A complete system is more than a fan. The components and their coordination with the building’s life safety systems typically include the following.

The fan is generally started by the fire alarm system, so the pressurization design depends on a well-specified fire alarm sequence of operation. Our fire alarm system design guide for Ontario developers and owners explains how these interfaces are documented. Where the fan must continue to run during a utility outage, the electrical design must include a supply from the emergency power system, with the load and transfer provisions identified at the outset. Our guide to emergency generator design in Ontario covers that side of the work.

Mechanical and electrical coordination often decides whether the stair system performs as drawn. The intake location, fan room, shaft routing, fire damper requirements and electrical feeders all compete for space in the design. Resolving them in schematic design is considerably cheaper than resolving them during construction review.

Conditions that affect performance

Several conditions can degrade a pressurization system after the design has been signed off.

Stack effect. In a Canadian winter, the temperature difference between a heated building and the outdoors drives air upward inside the building. This changes the pressure difference across stair doors at different heights, and it is the reason the design outdoor temperature matters. The 12 Pa minimum noted above is tied to situations where stack effect may dominate smoke movement.

Open doors. The number of doors open at once during evacuation is an assumption that should be stated in the design basis and reviewed by the authority having jurisdiction.

Wind. Wind on the building envelope can alter the pressure at the air intake and at relief openings. The location of intake and relief openings should be examined for the prevailing wind conditions at the site.

Leakage that differs from the assumption. Gaps around doors, unsealed penetrations and shaft construction can all raise or lower leakage. The NRC’s guidance that experts describe stair pressurization as highly complex, with building conditions changing during evacuation, supports the view that airflow capacity for open-door scenarios must be balanced against pressure relief for closed-door scenarios.

For readers working on design coordination, engineering support from specialists in smoke-control system design can complement local code review where a project involves multiple jurisdictions.

Testing and commissioning

Assumptions made at the design stage, particularly those about leakage areas, may differ from the conditions that are actually built. For that reason, post-installation testing is considered essential to verify that the design intent has been met.

A commissioning sequence for a pressurized stair normally includes:

1. Pre-functional checks: confirm the fan rotation, damper operation, sensor calibration, and the fire alarm signal that starts the system.
2. Pressure difference measurement: measure the difference between the stair and the adjacent floor with a pressure meter, with all doors closed, and then with the specified doors open.
3. Door force measurement: check the force required to open stair doors against the limit used in the design, since a system that meets its pressure target but traps occupants behind heavy doors has failed its purpose.
4. Airflow visualization: use tracer smoke or a punk stick to observe the direction of airflow around the stair doors, a method that the same Appendix B describes.
5. Emergency power test: verify that the fan restarts and operates on the emergency supply.
6. Documentation: record the measured values, set points and any adjustments so that the authority and the owner have a baseline for future tests.

Adjustments at this stage typically involve rebalancing dampers, changing relief settings or sealing leakage paths. When the as-built values differ significantly from the calculation, the designer should be involved in reviewing the cause, not only the contractor.

Periodic testing

Ongoing testing is a maintenance obligation. As an example from another province, the BC Fire Code requires that pressurized stair and elevator shafts be tested in different seasons at intervals of not more than two years, and after any building alteration. Ontario and Alberta set their own inspection and testing requirements through their fire codes, which owners should confirm with their fire protection consultant. The principle of retesting after alterations applies broadly: new partitions, tenant fit-outs and door replacements can all change leakage and therefore the system’s performance.

Our perspective

Stair pressurization is one of the clearest examples of a system that cannot be left to the end of the design process. The fan sits in the mechanical scope, the power and emergency supply sit in the electrical scope, the start signal sits with fire alarm, and the shaft construction sits with the architect. When these are developed separately, the permit review is where the conflicts surface.

We argue for a single coordinated design package, prepared by one team that understands mechanical, electrical and fire protection together. In our experience of new builds and renovations in Ontario, the projects that run smoothly are those where the leakage assumptions, the door-force limits and the generator loads are agreed before the drawings are issued for permit, and where field review is planned so that the commissioning test is a confirmation, not a discovery.

For owners, the practical advice is to treat the commissioning test as a design deliverable, to require measured results in the closeout documents, and to carry the same approach into any later renovation that touches the stair.

Sanjay

How FutureGen supports stair pressurization projects

FutureGen Consulting delivers mechanical and electrical design for residential and commercial projects in Ontario, including HVAC, fire protection and fire alarm design, fire and life safety design, and emergency power design, with permit-ready, engineer-stamped drawings and construction reviews. For a pressurized stair, that means the supply system, the fire alarm interface and the emergency power connection can be developed together under one engineering contract.

To discuss a project, see our fire protection and fire alarm system design services or our HVAC system design services.

Our construction review service can also be applied during installation, so that the leakage, damper and control conditions assumed in the design are checked against the work as it is built.

FAQ

How does stair pressurization work?

A dedicated fan supplies outdoor air to the stair, raising its pressure above that of the neighbouring floors. Air then leaks outward through door gaps instead of smoke leaking inward. The supplied air can also dilute smoke that entered before the system started or while a door was open.

How is a stairwell pressurization system tested?

Testing uses pressure meters to confirm the pressure difference across the stair doors, and tracer smoke or a punk stick to show the direction of airflow around them. Door-opening force, fire alarm activation and operation on emergency power are normally checked at the same time. Results are recorded as a baseline for later tests.

Why do stairs need to be pressurized?

In tall buildings, the stair is the main escape route and the route firefighters use to reach the fire floor. Pressurization helps keep it usable for longer. Whether it is required for a particular building depends on the code edition adopted in the province and on the building’s height, use and sprinkler protection.

What code applies to stair pressurization in Ontario and Alberta?

In Ontario, the Ontario Building Code and its supplementary standard SB-4 address smoke limitation in high buildings. In Alberta, the Alberta edition of the National Building Code and the Alberta Fire Code apply. Because provinces adopt model codes on their own schedules, the edition in force at permit application should be confirmed with a registered engineer.

Sources

• NRC: Air leakage data for the design of elevator and stair shaft pressurization systems
• NRC: Stair pressurization systems for smoke control
• NRC: Measures for fire safety in high buildings, 1977
• NIST: Smoke management
• Canadian Board for Harmonized Construction Codes: Provincial and territorial adoption
• Ontario Building Code: Limits to smoke movement
• British Columbia Building Code 2007, Appendix B, Division B
• BC Fire Code 2018, Division B, Section 7.3
• BC Government: single-egress-stair building requirements, 2024
• Fire safety in buildings and engineering projects

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