Fire Door Seals

Fire door seals are a critical component of passive fire protection in UK buildings. While the door leaf and frame provide structural resistance, it is the seals that help prevent fire and smoke from passing through the gaps around the door.

Inadequate, damaged or missing seals are one of the most common fire door defects identified during inspections. Understanding the different types of fire door seals, when they are required, and how they should be maintained is essential for compliance.

What Are Fire Door Seals?

Fire door seals are protective strips fitted around the perimeter of a fire-resisting door. Their purpose is to restrict the passage of fire and smoke through the small gaps necessary for the door to open and close properly. Without correctly specified seals, a fire door may not achieve its tested fire resistance performance.

There are two main types of seals used on fire doors:

• Intumescent seals – designed to expand when exposed to heat.
• Smoke (cold smoke) seals – designed to restrict smoke movement at normal temperatures.

Many modern fire doors use combined seals that provide both functions.

Types of Fire Door Seals

1. Intumescent Seals

Intumescent seals expand when exposed to high temperatures, typically during the early stages of a fire. As they expand, they fill the gap between the door and frame, helping to maintain the door’s fire resistance rating (such as FD30 or FD60).

These seals are tested as part of the overall fire door assembly under standards such as BS EN 1634-1 or BS 476 Part 22.

For a detailed explanation of how intumescent materials work, see our guide to intumescent strips for fire doors.

2. Smoke (Cold Smoke) Seals

Smoke seals, sometimes called cold smoke seals, are designed to reduce the spread of smoke before high temperatures cause intumescent expansion.

They are particularly important on doors classified as FD30S or FD60S, where the “S” indicates smoke control performance.

Smoke seals are often fitted as brush or blade inserts within the intumescent strip.

3. Combined Fire and Smoke Seals

Many fire doors use combined seals that incorporate both intumescent material and smoke control elements in a single strip.

These are commonly installed in communal residential blocks, offices, schools and other buildings where both fire resistance and smoke containment are required.

Seal Sizes and Specification

Fire door seals are available in different sizes and configurations, commonly 10mm, 15mm or 20mm widths with varying thicknesses depending on the door’s fire rating and test evidence. The correct size and type must match the door’s certification — fitting the wrong seal can invalidate performance.

When Are Smoke Seals Required?

Smoke seals are typically required where a fire door forms part of a protected escape route or where smoke control is specified under Building Regulations guidance such as Approved Document B.

Approved Document B expects fire doors protecting escape routes and compartment walls to perform as tested, which may include smoke control performance where specified.

They are commonly required on:

• Flat entrance doors in purpose-built blocks
• Doors protecting stairwells and protected corridors
• Higher-risk residential buildings subject to enhanced inspection duties

Requirements should always be confirmed against the door manufacturer’s certification and building-specific fire strategy.

How Fire Door Seals Are Installed

Most modern fire doors are pre-grooved to accept intumescent and smoke seals.

Installation should follow the door manufacturer’s certification and recognised guidance such as BS 8214 (Timber-based fire door assemblies – Code of practice).

Seals should:

• Run continuously around the top and vertical edges of the door
• Be correctly seated within the groove
• Not be cut short or discontinuous
• Not be painted over

Incorrect installation can compromise the fire resistance performance of the door.

Common Fire Door Seal Failures

Fire door seals are frequently identified as defective during inspections.

Common issues include:

• Missing or incomplete seals
• Damaged, split or worn seals
• Seals painted over, preventing expansion
• Incorrect seal size or specification
• Gaps caused by poor installation

Seal defects often appear alongside excessive door gaps, which can further undermine smoke and fire containment.

For wider context, see our guide to common fire door defects found during inspections.

Do All Fire Doors Need Seals?

Yes. All certified fire doors rely on correctly specified intumescent seals to achieve their fire resistance rating. However, not all fire doors require smoke seals — this depends on whether the door is required to provide smoke control (e.g. FD30S or FD60S classification).

Fire Door Seals and Compliance

Under the Regulatory Reform (Fire Safety) Order 2005, fire safety measures must be properly maintained. Fire doors that rely on intumescent or smoke seals must therefore be kept in efficient working order and checked as part of routine fire door inspections.

In England, additional inspection duties under the Fire Safety (England) Regulations 2022 require checks on flat entrance doors and communal fire doors in higher-risk residential buildings.

Failure to maintain fire door seals can result in non-compliance, enforcement action and increased risk to occupants.

Quick Summary

• Fire door seals restrict fire and smoke through door gaps.
• Intumescent seals expand in heat to maintain fire resistance.
• Smoke seals reduce cold smoke spread before fire conditions intensify.
• FD30S and FD60S doors require smoke control performance.
• Damaged or missing seals are a common inspection failure.
• Seal type and size must match the door’s certification and test evidence.

Conclusion

Fire door seals — including both intumescent and smoke seals — are fundamental to the performance of any fire door assembly.

Both intumescent and smoke seals must be compatible with the door’s certification and installed correctly to maintain compliance with UK fire safety guidance.

Frequently Asked Questions

Do all fire doors need smoke seals?

Not all fire doors require smoke seals. However, doors classified as FD30S or FD60S are designed to provide smoke control as well as fire resistance. Smoke seals are commonly required where doors protect escape routes such as stairwells and protected corridors.

What is the difference between intumescent seals and smoke seals?

Intumescent seals expand when exposed to heat, helping to maintain fire resistance during a fire. Smoke seals are designed to reduce the movement of cold smoke before high temperatures cause intumescent expansion. Many modern fire doors use combined seals that perform both functions.

Where are fire door seals fitted?

Fire door seals are typically fitted into grooves around the top and vertical edges of the door leaf or frame. They should run continuously and be correctly seated to ensure effective performance.

Can fire door seals be replaced?

Yes, damaged or missing seals can often be replaced. Replacement seals must match the door’s tested specification and certification. Incorrect seal type or size can affect the door’s fire resistance rating.

What happens if fire door seals are missing or damaged?

Missing or damaged seals can allow smoke and fire to pass through door gaps, reducing compartmentation performance. This is a common reason for fire door inspection failures.

Are fire door seals checked during inspections?

Yes. During structured fire door inspections, seals are checked for continuity, correct installation, damage and compatibility with the door’s certification.