Mixed-use developments combine residential, commercial and sometimes leisure — each with different fire safety requirements.
5 November 20244 min readFire Safety Services
The Fire Safety Challenge of Mixed-Use Development
Mixed-use buildings — those combining residential, commercial, retail, leisure, or other uses within a single structure — are among the most complex buildings to design for fire safety. Each occupancy type has different fire safety requirements, different occupant characteristics, different fire loads, and different evacuation strategies. Where these occupancies are combined in a single building, the fire strategy must address all of them coherently, managing the interactions between uses and ensuring that fire in one area cannot compromise the safety of occupants in another.
Code Conflicts and Design Challenges
The primary fire safety challenge in mixed-use buildings is that the applicable codes for each occupancy type may pull in different directions. Residential buildings use BS 9991 and typically operate a stay-put evacuation strategy. Commercial buildings use BS 9999 or Approved Document B and typically require simultaneous evacuation. Retail and leisure uses may require rapid simultaneous evacuation of large numbers of transient occupants unfamiliar with the building. Bringing these occupancies together in a single building requires careful engineering to manage the interactions.
Key design issues in mixed-use buildings include:
Compartmentation between uses — robust separation between residential and commercial occupancies is essential to prevent fire in the commercial areas compromising the residential stay-put strategy. Compartment walls and floors at the interface between uses typically require enhanced fire resistance.
Separate means of escape — residential and commercial occupancies should generally have separate means of escape, particularly for taller buildings. Shared staircases between residential and commercial uses can compromise both evacuation strategies and firefighting access.
Fire alarm strategy — the alarm strategy must address the different occupancies appropriately. Residential areas operating stay put should not receive alarming signals from commercial areas unless the fire has escalated to threaten the residential compartments. Commercial areas typically require immediate alarm and evacuation on fire detection.
Sprinkler provision — different occupancies may require different sprinkler specifications. Residential sprinklers designed to BS 9251 may not be appropriate for commercial areas, which may require more robust provision under LPC rules.
The most important fire safety principle for mixed-use buildings is separation. Robust compartmentation at the interface between uses — typically 60 minutes or more — is the foundation of a workable fire strategy for any mixed-use development.
Higher-Risk Mixed-Use Buildings
Mixed-use buildings containing residential units and exceeding 18 metres in height are classified as higher-risk buildings under the Building Safety Act 2022, regardless of the proportion of residential use. For these buildings, the full gateway process applies and the fire strategy must be submitted to and approved by the Building Safety Regulator at Gateway 2.
The BSR scrutinises the compartmentation between uses, the escape strategy for each occupancy, the interface between different alarm systems, and the firefighting facilities with particular care for mixed-use buildings. A fire strategy that does not clearly address each of these issues is unlikely to pass Gateway 2 without significant revision.
Residential Above Commercial: The Most Common Configuration
The most frequently encountered mixed-use configuration in UK development is residential apartments above commercial ground and first floors — typically retail, restaurant, or office use. In this configuration, the key fire safety considerations are: protection of the residential entrance and staircase from fire in the commercial areas; compartmentation at the residential/commercial interface; separate means of escape for residential and commercial occupants; and the firefighting strategy for both uses.
Frequently Asked Questions
Can residential and commercial occupancies share a staircase?
It is generally not recommended. Shared staircases between residential and commercial occupancies can compromise the stay-put strategy for residential occupants and the simultaneous evacuation strategy for commercial occupants. Where shared staircases are unavoidable, careful fire engineering is required to demonstrate that both strategies can be maintained.
What fire resistance is required at the residential/commercial interface?
The required fire resistance depends on the specific building configuration and the applicable codes, but 60-minute fire resistance is common at the interface between residential and commercial uses in mixed-use buildings, particularly for higher-risk buildings over 18 metres.
Do mixed-use buildings always require sprinklers?
Where the residential element is over 11 metres in height, sprinklers are required under BS 9991 for the residential areas. Commercial areas may also require sprinklers depending on the occupancy type and floor area. A fire engineer should advise on the sprinkler requirements for each occupancy.
How are fire alarms managed in mixed-use buildings?
Mixed-use buildings typically require separate but coordinated alarm systems for each occupancy. Residential areas typically have individual flat detectors with a common alarm for common parts. Commercial areas have simultaneous alarm systems. The systems must be coordinated to escalate appropriately if fire in one area threatens another.
Does the Building Safety Act apply to commercial parts of a mixed-use building?
The Building Safety Act 2022 applies to the building as a whole if it meets the higher-risk building criteria — over 18 metres or seven storeys with at least two residential units. The gateway process and BSR oversight apply to the entire building, including its commercial elements.
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