What Are Fire Door Seals?

Fire door seals are fitted around the edge of a fire door or within the door frame. Their purpose is to help close the gap between the door leaf and frame during a fire.

There are two main types:

Intumescent Strips

Intumescent strips expand when exposed to heat. This helps seal the gap around the door and slows the spread of fire and hot gases.

Smoke Seals

Smoke seals help restrict the movement of cold smoke around the door edges. They are usually supplied as brush, blade or fin-style seals and are often combined with an intumescent core.

In many buildings, fire and smoke protection are both needed, which is why combined intumescent fire and smoke seals are commonly used.

When Should Fire Door Seals Be Replaced?

Fire door seals should be replaced when they are no longer in good condition, no longer secure, or no longer suitable for the fire door.

You should consider replacing them if:

• Sections of seal are missing
• The strip is loose, cracked or peeling away
• The brush or fin smoke seal is damaged
• The seal has been painted over
• The door has been repaired or altered
• The seal has been cut badly around locks, latches or hinges
• The door no longer closes properly
• The seal is the wrong size for the door gap
• The door has failed a fire door inspection
• The seal does not match the door’s fire rating or specification

A fire door should be assessed as a complete assembly. Replacing the seals may help correct one issue, but it will not fix a damaged, warped or poorly fitted door.

Why Damaged Fire Door Seals Are A Problem

A fire door needs a controlled gap around the perimeter so it can open and close correctly. However, that gap can also allow smoke, flames and hot gases to pass through if the correct seals are not in place.

Damaged or missing seals can affect:

• Fire compartmentation
• Escape routes
• Smoke control
• Door certification
• Compliance during inspections
• The overall performance of the fire door set

Because fire doors are life safety products, poor-quality replacement work should not be treated as a cosmetic repair. The correct seal must be selected and fitted properly.

Fire-Only Seals Vs Fire And Smoke Seals

Before ordering replacement seals, check whether the door requires fire-only protection or both fire and smoke protection.

Fire-Only Intumescent Strips

Fire-only intumescent strips are designed to expand under heat and help restrict the spread of fire.

Fire And Smoke Seals

Fire and smoke seals combine intumescent material with a brush, blade or fin seal to help restrict cold smoke as well as fire.

As a general rule, if the existing seal has a brush, blade or fin, you should not replace it with a plain intumescent-only strip unless the door specification confirms that this is acceptable.

How To Check Existing Fire Door Seals

Before replacing anything, inspect the existing door and frame carefully.

Check:

• Where the current seals are fitted
• Whether they are in the door edge or frame
• The width and depth of the existing groove
• Whether the seal includes a smoke brush or fin
• The condition of the adhesive
• Whether paint or varnish has affected the seal
• Whether the door closes and latches properly
• Whether the perimeter gaps look consistent
• Whether hinges, locks or latches interrupt the seal

Take measurements before removing the old strip. This will make it easier to order the correct replacement.

What Size Intumescent Strip Do You Need?

The correct size depends on the fire door specification, the door’s fire rating and the existing rebate or groove.

You should not choose a seal based on appearance alone. Always check the fire door manufacturer’s instructions, test evidence, inspection report or project specification where available.

Rebated Or Surface-Mounted Fire Door Seals?

Replacement seals usually fall into two categories: rebated or surface-mounted.

Rebated Fire Door Seals

Rebated seals sit inside a groove in the door edge or frame. They usually provide a neat finish and are commonly found on prepared fire doors.

Choose rebated seals when:

• The existing door already has a suitable groove
• You are replacing like-for-like seals
• The door specification calls for rebated strips
• A flush finish is required

Surface-Mounted Fire Door Seals

Surface-mounted seals are fixed directly to the door frame or door edge. They can be useful where a groove is not present or where routing is not suitable.

Choose surface-mounted seals when:

• The door or frame is not already rebated
• Retrofitting is required
• Routing the door would not be practical
• The specified product is designed for surface application

Whichever option is used, the door must still open, close and latch correctly once the seals are fitted.

How To Replace Fire Door Seals

The exact process will depend on the product, so always follow the manufacturer’s instructions. As a general guide:

Step 1: Inspect The Door First

Check that the door is suitable for repair. If the door is damaged, warped, badly fitted or not closing correctly, replacing the seals alone may not be enough.

Step 2: Identify The Existing Seal

Check whether the current seal is fire-only or fire and smoke. Measure the width, depth and length, and note whether it is rebated or surface-mounted.

Step 3: Remove The Old Seal

Carefully remove the old strip without damaging the door edge or frame. Remove any leftover adhesive, dust, loose paint or debris.

Step 4: Clean And Prepare The Surface

The fitting surface should be clean, dry and sound. Adhesive strips should not be applied to dusty, greasy or unstable surfaces.

Step 5: Cut The New Seal To Size

Measure carefully and cut the replacement seal to suit the head and jambs of the frame or door edge. Use clean cuts and avoid leaving gaps at the corners.

Step 6: Allow For Ironmongery

Locks, latches, hinges and keeps may interrupt the seal. Cut neatly around these areas, but do not remove more of the seal than necessary.

Step 7: Fit The Seal

For self-adhesive seals, remove the backing gradually and press the strip firmly into place. Do not stretch the strip during fitting.

For mechanically fixed seals, use the fixings supplied or recommended by the manufacturer.

Step 8: Test The Door

Open and close the door several times. It should close fully, latch correctly and, where fitted, the door closer should still pull the door shut.

Common Fire Door Seal Fitting Mistakes

Poor fitting can reduce the effectiveness of the door. Avoid these common mistakes:

• Fitting the wrong size seal
• Replacing a fire and smoke seal with a fire-only strip
• Leaving gaps at the head or corners
• Cutting too much seal away around ironmongery
• Applying self-adhesive strips to dusty or greasy surfaces
• Painting over brush or fin smoke seals
• Fitting seals that stop the door from closing
• Using non-fire-rated draught excluders instead of certified fire door seals
• Ignoring existing door damage or excessive gaps
• Mixing different products without checking compatibility

Can You Paint Over Fire Door Seals?

You should avoid painting over smoke seals, brush seals or fin seals. Paint can clog the smoke seal and stop it working correctly.

Some intumescent materials may tolerate limited decoration depending on the product, but this should never be assumed. Always check the manufacturer’s guidance before painting around fire door seals.

Do You Need A Fire Door Inspection?

If fire door seals are missing, damaged or repeatedly coming loose, it may be worth arranging a fire door inspection. This is especially important in workplaces, flats, commercial buildings, schools, healthcare buildings and communal residential areas.

A competent inspection can identify whether the issue is limited to the seals or whether there are wider problems with the door leaf, frame, hinges, closer, glazing, signage or gaps.

Choosing The Right Replacement Fire Door Seal

When choosing replacement fire door seals, consider:

• The door’s fire rating
• Whether smoke protection is required
• Existing groove size
• Strip width and depth
• Door gap size
• Rebated or surface-mounted fitting
• Colour and finish
• Manufacturer test evidence
• Compatibility with the door assembly

Where possible, replace like-for-like using a product that matches the original specification. If the original seal is unknown, seek advice before ordering.

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