How to specify fire stopping

How do you specify fire stopping?

To specify fire stopping, give the fire resistance each seal must achieve, normally not less than the wall or floor it passes through, as a classification to BS EN 13501-2 from tests to BS EN 1366-3 for penetration seals or BS EN 1366-4 for linear joint seals. Then require a proprietary tested system whose evidence covers the actual substrate, opening size, services and orientation, installed by a third-party certified installer and labelled so it can be inspected later.

Approved Document B is plain about the aim: joints between fire-separating elements should be fire-stopped, and openings for pipes, ducts, conduits or cables through a fire-resisting element should be as few and as small as possible and fire-stopped. The difficulty is that a fire stopping seal only works in the situation it was tested in. A coated batt tested in a blockwork wall with copper pipes is not proven in a stud partition with plastic waste pipes and insulated ductwork, and most failures found on inspection come from that gap between the test and the opening on site.

This guide uses Uniclass Pr_25_80_81_51 Mineral wool fire-stopping, the coated batts and slabs used for large and mixed service openings and for many linear joints. Other parts of a fire stopping system have their own codes, such as Pr_30_31_76_40 Intumescent firestop sealants, Pr_65_52_61_86 Surface-mounted intumescent pipe collars and Pr_25_80_81_42 Intumescent linear gap seals. Cavity barriers are a different job, covered in the cavity barriers guide.

What does a fire stopping seal clause need to cover?

Some properties are specific to fire stopping. Others belong in every product clause. A clause that leaves either out gives the contractor room to substitute.

Fields marked Never guess depend on the project and should never be filled from a default or a previous job. If the information is not available yet, the clause should say so with a TBC and a reason.

Which decisions does the clause depend on?

Most properties follow from the product you choose. These depend on the project, so they need a decision from the designer before the clause is written.

Which standards should the clause cite?

Cite the product standard the declaration of performance refers to, the code of practice for installation, and the test method behind each value you set. A value without its test method cannot be checked against a submittal.

BS EN 1366-3

Fire resistance tests for service installations. Penetration seals

The test for penetration seals around pipes, cables and other services, including how far a result can be applied to other sizes and substrates. The current edition is 2021 with a 2024 amendment.

In the clause "Penetration seals: Tested to BS EN 1366-3, classified to BS EN 13501-2."

BS EN 1366-4

Fire resistance tests for service installations. Linear joint seals

The test for linear joint seals, covering joint width, orientation, splices and movement. Revised in 2021, with new rules on specimen size.

In the clause "Linear joint seals: Tested to BS EN 1366-4, classified to BS EN 13501-2."

BS EN 13501-2

Fire classification of construction products and building elements. Classification using data from fire resistance and/or smoke control tests, excluding ventilation services

The E and EI classes for penetration and joint seals, with pipe end configurations and joint parameters in the classification.

In the clause "Fire resistance: EI 60 to BS EN 13501-2."

BS EN 13501-1

Fire classification of construction products and building elements. Classification using data from reaction to fire tests

Reaction to fire classes, used for the support materials Approved Document B asks for.

In the clause "Support materials: Class A2-s3, d2 or better to BS EN 13501-1."

BS 476-20

Fire tests on building materials and structures. Method for determination of the fire resistance of elements of construction (general principles)

The national fire resistance test principles behind older fire stopping evidence. Approved Document B removes its national classes with the 2029 amendments, effective 2 September 2029.

In the clause Prefer European evidence on new work: "Classification to BS EN 13501-2. Evidence to BS 476 accepted only where permitted by Approved Document B at the time of building control approval."

ASFP Red Book

Fire-stopping: Linear joint seals, penetration seals and cavity barriers

Association for Specialist Fire Protection guidance on generic fire stopping systems, their suitability and test methods, referred to by Approved Document B.

In the clause Use it for guidance, not as the evidence: "Design and installation guidance: ASFP Red Book; performance to the classification reports."

BS EN ISO 10140-2

Acoustics. Laboratory measurement of sound insulation of building elements. Measurement of airborne sound insulation

The laboratory test behind the sound reduction figures manufacturers quote for seals in acoustic walls.

In the clause "Acoustic: Seal not to reduce the wall's sound insulation; submit Rw tested to BS EN ISO 10140-2."

Confirm the current edition of each standard at every issue. Avoice's State of UK Specifications 2026 found a withdrawn standard cited in 40% of specifications at contract issue.

For the regulations behind these choices, see Approved Document B explained, Higher-risk buildings explained, or search the Avoice Regulations library.

How do you write it in CAWS?

In CAWS, fire stopping is written in P12 Fire stopping systems. Recent NBS versions of P12 are arranged under General, System performance, Products and Execution, so the performance each type of fire stopping must achieve is set out once and the products are written as separate clauses. NBS lists coated mineral wool batts against P12 clause 360, Mineral wool rigid batts, with sealants, collars and pillows in their own product clauses.

The execution clauses at the back cover workmanship and installing particular products, such as clause 620 for workmanship generally and 680 for intumescent pillows. Fire stopping also depends on other sections: the services sections that create the openings, and L20 or K10 where doors and partitions meet the structure. Make sure those sections point to P12 rather than describing their own fire stopping.

Clauses the type clause relies on

P12/110

Fire stopping system The system performance clause: which elements need sealing and the classification each seal must reach.

P12/620

Workmanship generally Seal gaps between building elements and services; keep sealant off finished surfaces.

P12/680

Installing intumescent pillows Number and orientation of pillows, for openings where cables will keep changing.

Clause numbers vary between NBS versions and practice masters. Clauses 360, 620 and 680 follow published NBS material and an issued P12 specification; the 110 system clause number is typical rather than confirmed, so check it against your own P12.

How do you write it in Uniclass?

Uniclass separates fire stopping systems by what they seal. Ss_25_60_30_55 Multiple services penetrations fire-stopping systems describes a sealed opening with mixed services, while Ss_25_60_30_40 covers individual services, Ss_25_60_30_45 linear gaps and Ss_25_60_30_62 pipe collar systems. The system clause sets the classification, the substrate, the installer and the inspection regime. The batt, sealant and collars are product clauses it points to.

This fits how fire stopping is checked. An inspector looks at an opening, not a product, so the system clause gives one place to say what that opening must achieve and who is responsible for it. The product clauses carry the evidence the manufacturer supplies, and a change of manufacturer is checked against them.

In NBS Chorus, Uniclass product clauses also carry an NBS reference (for mineral wool fire stopping, 45-45-70/427). Use whichever your practice's masters use, but keep CAWS and Uniclass references out of the same specification.

What goes in the spec, and what goes in the schedule?

The specification defines each type once. The schedule and drawings say where each type goes.

What are the common mistakes?

Most problems are a missing property, a property filled with the wrong kind of value, or a decision left silently open.

• !
  "Fire stop all penetrations". With no classification, scope or responsibility, nobody can check it. Give the rating rule, the evidence and who seals what.
• !
  A system tested in blockwork used in drylining. Flexible walls are a different substrate. Check the evidence covers the wall type.
• !
  Mixed manufacturers in one seal. One firm's batt with another's sealant has no test behind it. Specify one system per seal.
• !
  Plastic pipes in a batt with no collar. Most plastic pipes need a collar or wrap to close as they soften. Check the evidence for pipe material and size.
• !
  Seals closed in before inspection. Once the ceiling is up, nobody checks. Set a hold point and photograph every seal.
• !
  Cavity barriers called fire stopping. Approved Document B treats them as different things. Specify cavity barriers separately.

How Avoice helps

Avoice drafts fire stopping clauses from your compartmentation drawings and services information, and marks what it could not confirm.

1. 1
   Drafts from your drawings

   It reads the fire ratings of walls and floors from the compartmentation drawings and writes P12 or Uniclass clauses with a classification rule per element, plus the product types the project uses.

2. 2
   Leaves an explicit TBC

   If the exposed seal colour or a seal type for an unusual opening is undecided, the clause says TBC with the reason, and it goes into the project TBC register to close before tender.

3. 3
   Uses your own clauses

   CAWS P12 or Uniclass, adapted from your practice's masters, keeping your numbering and wording.

4. 4
   Checks across sections

   QA/QC flags a services section that describes its own fire stopping instead of pointing to P12, a reference to a P12 clause that does not exist, or a withdrawn test standard.

5. 5
   Holds the evidence

   Classification reports and data sheets sit in the Product Room linked to each seal clause, and Approved Document B guidance is in the Avoice Regulations library.

Related guides: How to specify cavity barriers, How to specify intumescent paint, How to specify mineral wool insulation.

Software can draft and check. The designer still chooses the product and is responsible for the specification.