What is fire stopping and when is it required?

Fire stopping is the sealing of openings and gaps in fire-rated walls and floors to maintain their fire resistance. It is required wherever services (pipes, cables, ducts) penetrate fire-rated construction, and at junctions between fire-resisting elements. Approved Document B requires all penetrations through compartment walls, compartment floors and protected shafts to be fire-stopped to maintain the full fire resistance period of the element being penetrated.

Do plastic pipes need intumescent collars?

Yes, plastic pipes (PVC, ABS, PP, PE) passing through fire-rated walls and floors require intumescent collars or wraps. During a fire, the plastic pipe melts and the intumescent material expands to close the hole, preventing fire and smoke spread. For pipes up to 110mm diameter, a proprietary intumescent collar is standard. Wall penetrations typically need a collar on both sides, while floor penetrations need one collar on the soffit (underside). All collars must be third-party tested to BS EN 1366-3.

What fire stopping is needed for cable penetrations?

Cable penetrations through fire-rated construction must be sealed with tested fire stopping systems. For small cable bundles, intumescent mastic or sealant packed over mineral wool backing is standard. For larger openings such as cable trays, intumescent pillows or fire batt systems with coated sealant are used. Cable fill ratio must not exceed 60 percent of the opening area. All systems must be tested to BS EN 1366-3 and installed per the manufacturer tested specification.

How deep should a fire seal be?

The minimum depth of a fire seal depends on the product, fire rating and penetration type. Typical minimum depths are: intumescent sealant around metal pipes, 15-30mm; fire batt and sealant for larger openings, 50-100mm; intumescent pillows for cable trays, 100-200mm. The seal depth must match the manufacturer tested detail and is typically the full wall or floor thickness. Always follow the specific product installation guide as tested seal depths vary between manufacturers.

What records must be kept for fire stopping?

Under the Regulatory Reform (Fire Safety) Order 2005 and BS 8214, records must be maintained for all fire stopping installations. This includes: the product used and its reference number, the tested detail being replicated, the installer name and competency certification, date of installation, location within the building, and photographic evidence before concealment. Fire stopping should be inspected before being covered up. Many building control bodies and warranty providers require independent third-party inspection.

Fire Stopping Calculator — Service Penetration Fire Seals

Calculate fire stopping products and quantities for service penetrations through fire-rated walls and floors per Approved Document B.

Wall / Floor Type

Construction type of the fire-rated element

Service Type

Type of service penetrating the fire barrier

Required Fire Rating

Fire resistance period of the wall/floor being penetrated

Penetration Diameter / Width

Diameter of the service or opening

Number of Penetrations

Total number of similar penetrations

Annular Gap

Gap between service and edge of opening

How We Calculate This

This calculator selects the appropriate fire stopping product and installation method based on the service type, wall or floor construction, and required fire resistance period. It follows guidance from Approved Document B, BS EN 1366-3 and industry best practice.

How it works

Service type: Combustible services (plastic pipes) need intumescent collars to close the opening during a fire. Non-combustible services (metal pipes) only need gap sealing.
Wall/floor type: Masonry and concrete can use simpler sealant systems. Stud walls and timber floors need more robust fire batt solutions.
Fire rating: Higher fire ratings require greater seal depths and more robust products.
Penetration size: Larger openings need backing materials and may require pillow or batt systems instead of sealant alone.

Key standards

BS EN 1366-3: Fire resistance tests for service installations — penetration seals
BS 8214: Code of practice for fire door assemblies
Approved Document B: Fire safety requirements for buildings in England

Frequently Asked Questions

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Last updated: March 2026

All calculations are estimates. Verify with your supplier.