Pressurisation Systems

What is a Pressurisation System?

Pressurisation systems, also known as ventilation or air pressure control systems, are a type of smoke venting system designed to regulate the airflow and pressure within a building’s enclosed spaces.

The primary purpose of these systems is to pressurise zones within a building so that they are protected against the spread of smoke during a fire.

Typically, the areas served by a pressurisation system are the staircase, firefighting lift, and firefighting lobby. Protecting these zones ensures the safe evacuation of residents whilst also enabling firefighters to move safely throughout the building to extinguish a fire.

By directing air movement, pressurisation systems provide a viable solution to maintaining indoor air quality, controlling temperature and humidity levels, preventing the spread of contaminants, and ensuring occupants’ comfort and safety.

Legislation Regarding Pressurisation Systems

Approved Document B

Pressurisation systems are required by Approved Document B, as a solution that provides smoke ventilation in residential buildings.   

BS 9991

The recent draft BS 9991 proposes to require these systems in single-stair buildings taller than 18m, which has subsequently led to a surge in their adoption.

BS EN 12101-6 & BS EN 12101-13

The main reference document for designing and specifying pressurisation systems is BS EN 12101-6. Presently, it encompasses both the specifications for system components and instructions for system design.

However, in January 2022, the European Committee for Standardization endorsed BS EN 12101-13 – Smoke and Heat Control Systems Part 13: Pressure differential systems (PDS) – Design and calculation methods, installation, acceptance testing, routine testing, and maintenance – which will supersede the design aspect of BS EN 12101-6.

It is important to note that BS EN 12101-13, clause Air Intake, also advocates that the stair is ventilated from the basement level:

It is important to note that BS EN 12101-13, clause Air Intake, also advocates that the stair is ventilated from the basement level:“The air intake shall be located away from any potential fire hazards or smoke hazards (e.g. waste containers, basements smoke vents). Air intakes shall be located on ground level to avoid contamination by rising smoke.

NOTE: it is advisable that no building openings are situated below the air intake point.”

“The air intake should be located a minimum of 1m vertically below and 5m horizontally from any building openings (e.g. air outlets, windows, doors) or be in accordance with national requirements if these differ.

Glazing in these areas should have fire resistance in accordance with national requirements or E30 in accordance with EN 13501-2 as a minimum.”

“As an option, where air intakes on ground level are not possible then they can be positioned at roof level or elsewhere in the façade. For this application, there shall be at least two air intakes, spaced as far apart as possible and facing different directions in such a manner that they could not be directly downwind of the same source of smoke and/or as defined in national requirements. Each inlet shall be independently capable of providing the full air requirements of the PDS.”

How do Pressurisation Systems Work?

Depending on the building’s intended use, BS EN 12101-6 stipulates the system’s need to attain particular pressures and velocities. The system, in principle, works by supplying fresh air into the staircase via a supply fan. By maintaining a higher air pressure inside certain areas, such as stairwells or fire escape routes, compared to the surrounding spaces; this positive pressure differential helps prevent smoke from entering the protected areas during a fire emergency.

More specifically, for air to flow freely from the stair to the unsecured area, a mechanism is required. There are two ways in which this is typically achieved; either through natural smoke and heat ventilators as per EN 12101-2 or mechanical extraction as per EN 12101-3.

As per the diagram (to be added), in a pressurisation system, the ventilator serves to open and enable the passage of air. Without such a ventilator, if the door were to open, air would rush into the accommodation, causing the pressure to rapidly equalize with that of the stairwell, compromising protection.

Spatial Requirements for Pressurisation Systems

Within a structure, if the basement is over 10m deep a pressurisation system should be used.

Pressurisation systems require either a shaft or duct that serves the stairwell. The size of this shaft or duct will vary depending on whether it is intended for use as an escape route or as part of a firefighting system. Compliant buildings will typically feature a 0.5 to 1m2 single extract shaft. This area is calculated and influenced by the volume flow rate and the building height. For taller buildings, it’s often necessary to increase the shaft’s cross-section to prevent excessive airflow resistance within the system.

When pressurizing the lobbies, a corresponding shaft is required, usually small in size, typically around 0.15 to 0.2m². Regarding lifts, a riser is necessary only for buildings taller than 30 meters. For buildings below this height, air can be simply pumped in at either the top or bottom of the lift.

Types of Pressurisation Systems

There are primarily two types of pressurisation systems:

Positive Pressure Systems:

Negative Pressure Systems:

Components of Pressurisation Systems

Pressurisation systems typically consist of several components working together to control airflow and pressure differentials:

Ventilation Fans

These fans either supply fresh air into the building (positive pressure) or exhaust stale air out of the building (negative pressure).


Channels air between the ventilation fans, air handling units, and various spaces within the building.

Air Handling Units (AHUs):

AHUs condition the incoming air by heating, cooling, humidifying, or dehumidifying it as needed before distributing it throughout the building.

Controls and Sensors

Monitoring devices and control systems regulate the operation of the pressurisation system, adjusting airflow rates, temperature settings, and pressure differentials based on occupancy levels, indoor air quality, and other parameters.

Benefits of Pressurisation Systems

Pressurisation systems offer several benefits, including:

Enhanced Indoor Air Quality

By controlling airflow and ventilation rates, pressurisation systems help remove pollutants, allergens, and contaminants from indoor environments.

Improved Comfort

Maintaining balanced airflow and temperature levels ensures occupant comfort and productivity.


Optimising ventilation rates and airflow distribution reduces energy consumption and HVAC system operating costs.

Containment of Contaminants

Negative pressure systems prevent the spread of airborne contaminants, pathogens, and odors, enhancing occupant safety and health.

Protection of Sensitive Environments

Positive pressure systems maintain cleanroom conditions by preventing the infiltration of outside contaminants, ensuring the integrity of critical processes and equipment.

Why choose a pressurisation system

Overall, pressurisation systems play a vital role in maintaining healthy, comfortable, and sustainable indoor environments in residential, commercial, and industrial buildings.

If you require a pressurisation for your upcoming project, get in touch with FDS today.