Fire compartmentation is the primary means of limiting fire spread in a building. Here's what it involves, how it fails, and why the fire strategy must get it right.
4 March 20254 min readFire Safety Services
What Is Fire Compartmentation?
Fire compartmentation is the division of a building into separate fire-resistant zones using walls, floors, doors, and other construction elements that are designed to contain fire and smoke within a defined area for a specified period. It is the primary passive fire protection measure in any building and is fundamental to both occupant safety and property protection.
The principle is straightforward: by containing a fire within the compartment in which it starts, compartmentation buys time for occupants to escape, limits fire spread to adjacent areas, and allows firefighters to tackle the fire safely. For higher-risk buildings — particularly residential towers — compartmentation is the cornerstone of the fire safety strategy, supporting stay-put evacuation policies and protecting the means of escape.
How Compartmentation Works
Compartmentation works through a combination of fire-rated construction elements that resist the passage of flame and hot gases. The key components are:
Fire-rated walls and floors — constructed from materials with sufficient fire resistance to contain a fire for the required period. The fire resistance period depends on the building type, height, and occupancy — typically 30, 60, 90 or 120 minutes for residential and commercial buildings.
Fire doors — self-closing fire-resisting doors that maintain compartmentation at openings. Most residential buildings require FD30 (30-minute) or FD60 (60-minute) fire doors. Fire doors must be self-closing, must not be held open except by approved hold-open devices, and must be maintained in good condition.
Fire stopping — sealing of service penetrations through fire-rated walls and floors. Every pipe, cable, duct, and conduit that passes through a compartment wall or floor must be fire stopped to prevent fire and smoke spreading through the gap.
Cavity barriers — fire-resisting barriers installed within cavities in external walls and roof spaces to prevent unseen fire spread through concealed voids.
Critical point: A compartmentation strategy is only as effective as its weakest element. A single unsealed service penetration, propped fire door, or damaged door seal can allow fire and smoke to spread throughout a building in minutes.
Compartment Sizes Under UK Regulations
Approved Document B and BS 9999 set maximum compartment sizes for different building types. For residential buildings, each flat is typically required to be a self-contained fire compartment — meaning that fire in one flat should not spread to adjacent flats or the common parts for the specified fire resistance period. For commercial and industrial buildings, maximum floor areas and volumes are specified depending on the occupancy and sprinkler provision.
For higher-risk residential buildings over 18 metres, BS 9991:2015 sets more stringent requirements including 60-minute fire resistance for compartment walls and floors (as opposed to the 30-minute standard for lower buildings) and specific requirements for firefighting shafts and lobbies.
Common Compartmentation Failures
Fire compartmentation failures are among the most common fire safety deficiencies found in existing buildings. The most frequent issues are:
Unsealed service penetrations — the single most common failure. Every pipe and cable that passes through a compartment wall must be fire stopped with an intumescent collar, sealant, or other approved system.
Damaged or missing fire doors — fire doors that are damaged, held open, have defective closers, or have missing intumescent strips and smoke seals cannot perform their compartmentation function.
Alterations without building control approval — partitions removed, doors replaced with non-rated equivalents, services rerouted through compartment walls without fire stopping.
Ceiling voids — fire resistance of floors can be compromised if suspended ceiling systems do not form part of the fire-rated assembly or if the void above is not properly compartmented.
Compartmentation and the Building Safety Act 2022
For higher-risk buildings, the Building Safety Regulator requires detailed compartmentation information as part of the Gateway 2 submission. This includes specifications for compartment wall and floor construction, fire door schedules, fire stopping specifications, and cavity barrier details. For existing higher-risk buildings, compartmentation surveys are increasingly required as part of building safety case preparation.
Frequently Asked Questions
What fire resistance period do compartment walls need?
The required fire resistance period depends on the building type and height. For most residential buildings, 30 minutes is standard for compartment walls between flats. For buildings over 18 metres, BS 9991 typically requires 60 minutes. Your fire strategy will specify the periods applicable to your building.
How do I know if my building's compartmentation is adequate?
A compartmentation survey carried out by a competent fire engineer will assess the existing provisions against applicable standards. This typically involves visual inspection and targeted intrusive investigation to verify construction details in areas where surface inspection is insufficient.
Do fire doors need to be self-closing?
Yes. Fire doors in compartment walls must be self-closing to ensure they close automatically in the event of a fire. Doors held open by wedges or other devices are not performing their fire safety function and are a regulatory offence under the RRO 2005.
What is fire stopping and who is responsible for it?
Fire stopping is the sealing of service penetrations through fire-rated walls and floors. It is the responsibility of contractors to install fire stopping correctly during construction and the responsibility of the building owner or managing agent to maintain it in an occupied building.
Can I see the compartmentation strategy for my building?
For higher-risk buildings, residents have a right to certain fire safety information under the Building Safety Act 2022. The fire strategy, which includes the compartmentation strategy, forms part of the golden thread of building information that accountable persons must maintain.
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