Passive fire protection · Nationwide
Cavity Barriers - Installation & Remediation
Nationwide
Fire spreads fastest where you can't see it. The concealed cavities in external walls, roof spaces and voids are hidden motorways for fire and smoke - unless they're closed off. MGN Group installs and remediates certified cavity barriers that seal those routes, keeping fire contained to the compartment where it starts. Surveyed, installed and documented across the UK.
- 25
- Years in passive fire protection
- 100%
- Certified barrier systems
- UK-wide
- Coverage
- 48h
- Average response time to enquiries
What we do
Cavity Barriers - Closing the Hidden Routes for Fire
A cavity barrier does a simple, vital job: it divides a concealed void so fire and smoke can't travel through it unchecked. The problem is that these barriers are often missing, wrongly specified, or damaged by later trades - and because they're hidden, nobody knows until a survey or a fire reveals it. MGN surveys, installs and remediates cavity barriers to certified standards, and documents every one, so the hidden parts of your building are as protected as the parts you can see. They work hand in hand with fire stopping, which seals the penetrations through your compartment walls.
Cavity Barriers to External Walls
Installation of certified cavity barriers within external wall build-ups and rainscreen systems, closing the vertical and horizontal routes fire can take through the facade.
View external wall barriersOpen-State Cavity Barriers
Ventilated cavity barriers that stay open to allow airflow in normal use and close in a fire - for drained and ventilated rainscreen cavities.
View open-state barriersRoof Void & Concealed Space Barriers
Sub-dividing roof voids, ceiling voids and other concealed spaces to limit the size of any undetected fire.
View void barriersRemedial Cavity Barrier Works
Correcting missing, damaged or incorrectly installed barriers identified in a survey or fire risk assessment - a common and critical remediation.
View remedial worksSurvey, Inspection & Certification
Surveying concealed cavities, and certifying and documenting every barrier installed for your fire safety file and golden thread.
View survey & certificationNew Build Cavity Barriers
Installation coordinated with the facade and main contractor's programme, with handover documentation for building control.
View new build
What we cover
Where Cavity Barriers Matter Most
Concealed cavities exist in almost every modern building, but the stakes are highest where people sleep and where buildings are tall:
High-Rise Residential
External wall cavity barriers in high-rise blocks - the most scrutinised area of building safety, and central to remediation programmes.
Education & Healthcare
Concealed voids in schools, colleges and healthcare estates, remediated around live use.
Commercial & Mixed-Use
Rainscreen and clad facades on offices, retail and mixed-use developments.
Housing & Apartments
Flatted and low-rise residential, where cavity barriers protect the compartmentation between homes.
New Build Developments
Correctly specified and installed cavity barriers from the outset, coordinated with the facade package.
Facilities Management
Survey-and-remediate programmes for FMs responsible for existing building stock.
Our credentials
Certified Systems, Documented Installs
Because cavity barriers are hidden once the facade is closed, certification and documentation are the only proof they were installed correctly.
Certified Barrier Systems
We install manufacturer-tested, certified cavity barrier systems, matched to the cavity type and fire performance required.
Third-Party Certification
Independent certification of our passive fire protection work. [Confirm the exact schemes MGN holds for this discipline before publishing.
CHAS Accredited
Health, safety and compliance pre-qualification for safe working on client sites.
Documented & Traceable
Photographic records and certification for every barrier, supporting your golden thread of building safety information.
Client trust
Trusted on UK building safety projects - what our clients say
“We were very pleased with the partitions and ceiling works carried out for our fit-out. The team were professional, reliable and delivered a high standard of workmanship throughout the project. We’re really happy with the finished result and would happily recommend their services.”
Tribe Yoga
- Partitions
- Ceilings
- Fit-out
“We were very pleased with the door installation and remedial works carried out at Balquhidder House to ensure the property aligned with compliance requirements. The team were professional, reliable and completed the work to a high standard, with excellent attention to detail throughout. We’re very happy with the finished result and would happily recommend their services.”
Balquhidder House
- Fire doors
- Remedial works
“We were very pleased with the firestopping works carried out at Thornton Care Home. The team were professional, reliable and completed the work to a high standard.”
Thornton care home
- Fire stopping
Regulations
The Rules on Concealed Cavities
Cavity barriers are a Building Regulations requirement, and one of the areas most affected by post-Grenfell reform:
Approved Document B (B3 - Internal Fire Spread)
Building Regulations require cavity barriers to be provided to close concealed spaces and sub-divide cavities, limiting the hidden spread of fire and smoke.
Building Safety Act 2022 & the “golden thread”
For higher-risk buildings, duty-holders must hold evidence that external wall systems - cavity barriers included - are correctly specified and installed, making documented work essential.
Fire (Scotland) Act & Building Standards
Equivalent requirements for the sub-division of cavities apply in Scotland - MGN Group's home jurisdiction.
This summary is not legal advice - your own fire risk assessment and building safety case set out the specific duties for your building.
Quick answers
A fire-resisting barrier fitted inside a concealed space - an external wall cavity, roof void, ceiling void or floor void - to stop fire and smoke travelling through it unseen. It closes the void at compartment lines, around openings and at set intervals, so a fire cannot bypass the walls and floors that are supposed to contain it.
Approved Document B requires them at the edges of cavities, around openings such as windows and doors, at the junctions with compartment walls and floors, and to sub-divide extensive cavities. In practice that means external wall build-ups and rainscreen systems, roof and ceiling voids, and any large concealed space.
A barrier that stays partly open in normal use so a drained and ventilated rainscreen cavity can still breathe, then closes in a fire as its intumescent element expands. It resolves the conflict between the ventilation the facade needs and the fire separation the regulations require.
Fire stopping seals the openings and joints where services or gaps pass through a fire-resisting wall or floor. A cavity barrier sub-divides or closes off the concealed space within a construction, so fire cannot travel through the void itself. Most compartmentation programmes need both, and MGN delivers them under one contract.
They should be inspected during installation - because once the facade or ceiling is closed they can't be seen - and revisited whenever a survey, fire risk assessment or building safety case questions the external wall build-up. That is why photographic records and certification at the time of install matter so much.
Request a Cavity Barrier Survey
Whether you're building new, remediating an existing facade or responding to a building safety case, we'll survey the concealed cavities and give you a clear, certified plan. Fast, no-obligation quote.