Technical guide
Fire ratings for modular buildings in the UK
A clear guide to fire-rated modular buildings, including EI, REI, FD fire doors, detection systems, compartmentation, Approved Document B and the documents usually needed for Building Control review.
Fire performance is project-specific. The right specification depends on building use, occupancy, layout, storeys, escape strategy, location, neighbouring risks, services and the approval route.
Short answer
What fire ratings mean for modular building projects
Fire ratings describe how long a wall, floor, frame, door or other building element can resist fire. For modular buildings, they must be considered alongside the full fire strategy: means of escape, alarms, compartmentation, structural resistance, external fire spread and fire-service access.
Important: do not treat any single rating as automatic compliance. A project may require different fire ratings depending on its use, occupancy, layout, storeys, escape distances, site boundary conditions and Building Control requirements.
Rating types
The main fire rating codes: E, I and R
Fire ratings normally use letter codes and time periods. The correct combination depends on the element being specified and the role it plays in the fire strategy.
Integrity
Integrity measures how long an element resists flames and hot gases passing through. It is a core part of fire-separating walls, doors and compartment lines.
Insulation
Insulation measures how long the unexposed side limits temperature rise. This matters where heat transfer could endanger people, contents or adjacent spaces.
Load-bearing resistance
Load-bearing resistance measures how long a structural element can continue to support its load during fire exposure. It is relevant to frames, floors and structural systems.
Part B context
Approved Document B and modular buildings
Approved Document B gives fire safety guidance for meeting Building Regulations requirements in England. Modular buildings still need project-specific fire safety review; off-site manufacture does not remove the need for a suitable fire strategy.
B1 — Warning and escape
Covers fire detection, alarm strategy, escape routes and the ability of occupants to leave safely. Modular projects may need Category L detection, emergency lighting and clear exit routes depending on use.
B2 — Internal fire spread: linings
Considers surface spread and the fire performance of internal linings. The chosen wall and ceiling finishes should be checked against the final use and escape strategy.
B3 — Internal fire spread: structure
Considers structural fire resistance and compartmentation. This is where frame rating, floors, walls, doors and service penetrations must be coordinated.
B4 and B5 — External spread and fire-service access
External wall performance, boundary distance, roof classification and fire-service access need to be reviewed against the site layout, neighbouring buildings and fire strategy.
Specification note: where a project needs enhanced fire resistance, ask for the relevant test reports, classifications, installation instructions and project-specific confirmation before relying on any rating in tender or approval documents.
Fire-rated specification
Building elements that should be checked
A safe fire-rated modular building is not created by one component. The rating of panels, frames, doors, alarms, seals, service penetrations and external finishes must work together.
Wall and roof panels
Panel fire performance should be confirmed using the exact panel type, thickness, jointing system and installation method proposed for the project.
Structural frame
Steel-frame or other structural systems may need fire resistance depending on the building use, number of storeys, compartmentation and structural strategy.
Fire doors and openings
Fire doors should match the compartment and escape-route strategy. Door ratings, smoke seals, intumescent strips, glazing and ironmongery must be compatible.
Detection and alarms
Fire detection and alarm systems should be designed, installed, commissioned and documented for the specific building use and occupancy profile.
Service penetrations
Ducts, pipes, cables and other penetrations through fire-resisting elements need suitable fire stopping and documented installation details.
External envelope
Cladding, roofing and façade materials should be reviewed with boundary distances, use class, height, occupancy and the wider fire strategy in mind.
Specification routes
Typical fire rating considerations by project type
These are design considerations, not fixed universal promises. The final specification should be confirmed through drawings, calculations, certificates and approval comments.
| Project type | Likely fire-safety focus | Items to confirm early |
|---|---|---|
| Modular offices | Escape routes, compartment lines, detection, emergency lighting and fire-door schedule. | Occupancy, open-plan areas, fire exits, internal rooms, services and intended duration. |
| Modular classrooms | Evacuation of groups, escape route clarity, internal finishes, fire doors and detection coverage. | Student age, supervision, school estate strategy, access routes and any education-sector guidance. |
| Healthcare or clinical modules | Patient vulnerability, progressive horizontal evacuation, enhanced detection and compartmentation. | Clinical use, mobility profile, alarm interface, fire strategy, NHS or healthcare-specific requirements. |
| Welfare units and site accommodation | Warning systems, escape, electrical safety, heating, cooking areas and site-management rules. | Temporary/permanent status, workforce numbers, power supply, layout, cooking provision and site fire plan. |
| Residential, lodges or sleeping accommodation | Sleeping risk, smoke detection, internal escape, fire separation and external spread. | Use class, occupancy, planning status, standards route, escape windows, alarms and management responsibilities. |
Documentation
What to request before approval or installation
A premium modular building supplier should be able to explain what is included, what is excluded and what must be confirmed by the designer, fire engineer, Building Control body or client-side team.
Ask for project evidence
- Fire strategy or fire-safety design notes where required
- Panel classification and relevant test evidence
- Fire-door schedule and door certificates
- Alarm category, design certificate and commissioning evidence where relevant
- Fire stopping details for service penetrations
- Emergency lighting and signage information where included
- Drawings showing escape routes and compartment lines
Clarify scope boundaries
- Who is responsible for the full fire strategy?
- Who submits to Building Control?
- What is factory-fitted and what is site-fitted?
- Who signs off site fire-stopping works?
- Who maintains alarms, doors and emergency lighting after handover?
- What assumptions are used for occupancy and final use?
External guidance
Useful UK fire safety references
These external resources help clients understand the fire-safety approval context. They do not replace project-specific advice from Building Control, a competent designer or a fire engineer.
GOV.UK Approved Document B
Government fire safety guidance for the Building Regulations in England.
GOV.UK Approved Documents
The wider set of building regulation guidance documents used for design and compliance planning.
BSI BS 5839 series
British Standards information for fire detection and fire alarm systems for buildings.
FAQ
Fire ratings for modular buildings FAQ
Answers to common questions about fire-rated modular buildings, fire doors, alarms, documentation and Part B review.
What do fire ratings mean in modular buildings?
Do modular buildings need to meet Approved Document B?
Are FD30 and FD60 fire doors always required?
What information is needed to specify fire-rated modular buildings?
Can fire-rated modular buildings be used for education, healthcare or public-sector projects?
Need a fire-rated modular building specification?
Send KC Modular Buildings the intended use, location, layout, occupancy, fire-safety comments and any Building Control requirements. The team can then discuss the most suitable modular system, specification route and documentation package.