Intumescent Strips Regulations (UK)

Problems with seals are among the most frequently recorded fire door defects in inspections and Fire Risk Assessments (FRAs).

This page is for landlords, managing agents and facilities managers who need to understand what intumescent strips do, how they differ from smoke seals and what inspectors typically expect to see in practice.

There is often confusion between fire seals and smoke seals. They are related, but they do not always perform the same function.

What are intumescent strips?

Intumescent strips are components fitted to many fire doors to help resist the spread of fire.

When exposed to high heat, the material expands. This helps to close gaps around the door and support the door assembly’s fire-resisting performance.

They are commonly fitted:

• in the frame
• in the edge of the door leaf
• around glazing systems where appropriate

Their purpose is to help maintain the integrity of the fire-resisting assembly during a fire.

What are smoke seals?

Smoke seals are used to help limit the passage of smoke, particularly in the earlier stages of a fire.

They are often fitted as part of, or alongside, an intumescent seal arrangement.

Inspectors may refer to them separately because a door can have:

• intumescent protection for fire resistance, and
• additional smoke control features where required

This is why reports may specifically mention missing or damaged smoke seals rather than only referring to intumescent strips.

Are smoke seals always required?

Not always in every case.

Whether smoke seals are expected depends on factors such as:

• the type of fire door
• the location of the door
• whether smoke control is part of the intended performance
• the original specification or certification of the door set

In practice, inspectors will usually assess whether the door appears to have the correct type of seal arrangement for its intended use.

What inspectors typically check

During a fire door inspection, assessors commonly look for:

• missing sections of seal
• seals that are damaged, worn or detached
• seals painted over
• incorrect seal profile or type
• breaks in continuity around the door perimeter
• signs that seals have been replaced inconsistently

They may also consider whether the seal arrangement appears suitable for the door’s intended fire and smoke performance.

Common seal-related findings in Fire Risk Assessments

Typical report wording may include:

• “Intumescent seals damaged”
• “Smoke seals missing”
• “Seals painted over”
• “Incorrect seal type fitted”
• “Continuity of seals compromised”

These are common inspection findings and are often treated as remedial items requiring correction within a reasonable timeframe.

Why damaged or painted-over seals matter

Even relatively small seal defects can affect how the door performs in a fire.

Inspectors often record concerns where seals are:

• brittle
• cut short
• loose in the groove
• painted over
• crushed, torn or worn away

In everyday building use, these problems can develop gradually and may not be noticed until the door is checked in detail.

Can intumescent strips be replaced?

Often, yes, where replacement is appropriate for the particular door and seal arrangement.

However, replacement should not be treated as a one-size-fits-all exercise. The correct seal type, size and profile should be suitable for the door assembly in question.

Where there is uncertainty, competent advice should be obtained rather than assuming that any replacement strip will be acceptable.

How seal defects are typically addressed

Depending on the issue, remedial action may involve:

• replacing damaged seals
• reinstating missing sections
• removing paint contamination where appropriate
• checking continuity around the door
• confirming the correct seal type has been used
• reinspecting the door after repair

The exact remedial action should align with the Fire Risk Assessment and the specification of the door set.