A firestopping specification is tested long before a sealant gun reaches site. For project teams asking how to specify firestopping, the central task is not choosing a familiar product. It is defining a verified solution for every service penetration, linear gap and construction joint that could compromise a fire-resisting compartment.
That distinction matters. A neat-looking seal around a pipe may still fail if the substrate, annular space, service insulation, movement requirement or installation depth differs from the tested arrangement. In a fire, passive fire protection is the final barrier between a developing incident and the people, property and livelihoods it threatens. The specification must therefore control the detail, the process and the evidence.
Start with the compartmentation strategy
Firestopping should follow the building’s compartmentation design, not be treated as a late-stage package to close gaps left by other trades. Establish the fire-resisting walls, floors, shafts, risers and cavity barriers that form the intended lines of protection. Then identify every point at which those elements are interrupted by services or adjoining construction.
The required fire resistance period must be taken from the project fire strategy and the applicable regulatory pathway. For many projects this will involve the functional requirements of the Building Regulations and the guidance in Approved Document B, alongside the project-specific fire strategy, insurer requirements and client standards. Existing buildings, change-of-use schemes, listed assets and infrastructure environments often demand a more detailed assessment because construction may not match original drawings.
A specification should clearly state what is being protected: integrity, insulation, smoke leakage performance where relevant, and the required duration. It should also distinguish between compartment walls and floors, protected shafts, service risers and other locations with different performance requirements. A generic note calling for “fire-rated mastic to all penetrations” does not provide a safe or auditable instruction.
Define each opening as a tested system
The most reliable way to specify firestopping is to work from the opening outwards. Record the supporting construction first: its material, thickness, density, build-up and rated performance. A seal tested in a rigid concrete slab cannot automatically be transferred to a lightweight partition, CLT panel, heritage lath-and-plaster wall or composite floor construction.
Next, define the penetrating service and its configuration. This includes the service type, size, orientation, number of services, insulation, spacing, whether it is combustible or metallic, and whether it is expected to move. A mixed-service opening containing cables, cable trays, plastic pipework and insulated copper services requires a tested detail that addresses the complete arrangement, not a series of assumptions applied around each item.
The proposed system should be supported by relevant test evidence, assessment or classification documentation. The detail needs to match the site condition within the permitted scope of that evidence. If it does not, the design team should seek a suitable engineered solution from an appropriately qualified source before installation proceeds.
Allow for movement, maintenance and future change
A firestopping detail has to remain effective during the building’s working life. Linear joints can be subject to structural movement, deflection and thermal expansion. Service penetrations may need access for replacement, upgrades or additional cabling. In healthcare, data, hotel, transport and commercial buildings, service density can change rapidly after handover.
This is where system selection becomes a practical judgement. Mortar-based solutions may suit stable, small openings in masonry or concrete, while coated batt systems can offer controlled flexibility where multiple services are present. Intumescent collars or wraps may be needed around combustible pipes, and ablative coatings, pillows or modular systems can be appropriate where regular service alterations are anticipated. The right answer depends on the tested construction and the operational requirement, not on product familiarity or initial cost alone.
Write a firestopping specification that can be built
A strong specification translates design intent into instructions that site teams can act upon. It should identify the required fire performance, the approved system manufacturer or system type, the relevant tested detail reference, permitted substrates and services, installation method, and any restrictions on spacing or aperture dimensions.
It should also address interfaces. Firestopping failures frequently occur where one fire-protection measure meets another: a service seal at a shaft wall, a linear joint beneath a curtain wall, a penetration through a fire-resisting ceiling void, or a cavity barrier meeting an irregular façade build-up. These are not minor details. They are locations where discontinuity can allow fire and smoke to bypass the compartment line.
For complex schemes, a penetration schedule is invaluable. Each opening can be given a unique reference, location, construction type, service description, required rating, tested-system reference and status. This gives the main contractor, specialist installer, clerk of works and building owner a common record. It also reduces the risk of details being improvised in risers, plant rooms and concealed voids where access later becomes difficult or disruptive.
Avoid open-ended clauses such as “or equivalent” unless equivalence is controlled through formal technical review. Firestopping products are not interchangeable simply because they carry similar ratings. A substitution can alter the tested configuration, and that may invalidate the intended performance.
Set responsibilities before work starts
The firestopping contractor should not be asked to resolve every undocumented site condition after first fix. Equally, designers cannot rely on a drawing note without ensuring that the installed detail can be evidenced. Clear allocation of responsibility is essential.
The design team should establish the compartmentation intent and performance requirements. The main contractor should coordinate sequencing, access, opening management and trade interfaces. MEP contractors should provide accurate service information and avoid unauthorised additions after seals have been installed. The specialist passive fire protection contractor should verify site conditions, install approved systems and raise discrepancies where the design evidence does not fit the opening.
Pre-installation surveys are particularly valuable on refurbishment and heritage projects. Hidden voids, uneven substrates, undocumented services and fragile historic fabric can change the solution completely. Early survey work allows the project team to protect the building fabric while selecting a firestopping approach that remains compliant and practical to install.
Specify competence, inspection and evidence
Firestopping is safety-critical work. The specification should require installers with demonstrable product training, relevant passive-fire expertise and, where appropriate, third-party approval. Competence is not only about applying a product correctly. It includes recognising when a proposed detail is outside its tested limits and escalating it before a defect is concealed.
Inspection needs to be planned, not left to the end of the programme. Agree hold points for representative first installations, complex service zones and concealed areas. Inspections should check the substrate condition, annular gap, depth of seal, service arrangement, backing materials, product identification and labelling. Photographic records are useful, but they should support rather than replace physical inspection.
The handover record should be sufficiently detailed for future management. This commonly includes marked-up drawings, penetration schedules, system references, installation records, inspection reports, photographs, product data and evidence of installer competence. For higher-risk buildings, information management duties and the wider golden-thread approach make accurate, traceable records even more significant.
Treat changes as a design issue, not a snagging issue
Late services are one of the most common threats to compartmentation. A new cable tray, oversized pipe penetration or revised duct route can turn a compliant detail into an untested arrangement. The response should not be to fill the opening with whatever material is available.
Set a change-control process that requires revised openings to be surveyed, matched to suitable evidence and recorded before they are closed. This may appear slower during fit-out, but it is considerably less costly than opening ceilings, risers or occupied areas after practical completion to investigate untraceable seals.
For main contractors and building owners, the value lies in control. A well-specified firestopping package protects programme certainty as well as life safety because expectations are clear before installation starts. It gives every party a defensible route from fire strategy to installed, inspected and documented compartmentation.
The best time to resolve a firestopping detail is when the wall or floor is still visible, the services are known and the correct tested system can be installed without compromise. Treat that moment as a safety decision, not a finishing task.
