What Are Fire Door Strips?
Fire door strips (also called intumescent strips) are narrow strips fitted into a groove around the edge of a fire door. In normal conditions they are virtually invisible. When exposed to heat, they expand up to 20 times their original size, sealing the gap between the door and frame to block fire and smoke.
Without working intumescent strips, a fire door offers almost zero protection — hot gases and fire simply pass through the gap around the door edge.
UK Legal Requirement — All certified fire doors in the UK must have intumescent strips fitted. Under Building Regulations Part B, missing, damaged or painted-over strips result in a non-compliant fire door.
Intumescent Strips vs Smoke Seals
Intumescent Strips (Fire Protection)
Expand in heat to seal the door edge against fire. Usually beige or cream coloured. Activate at around 150-200°C. Essential for FD30, FD30S, FD60 and FD60S doors.
Smoke Seals (Cold Smoke Protection)
Block smoke at normal temperatures before the intumescent strip activates. Usually black brush or rubber fins. Legally required on all FD30S and FD60S doors in residential properties.
✓ The S In FD30S: The "S" stands for smoke. FD30S doors must have BOTH intumescent strips AND smoke seals. Smoke kills more people in fires than flames — which is why residential fire doors must be smoke-rated.
Types Of Fire Door Strips
Single Strip (10mm)
Fits into a 10mm groove. Standard for most FD30 doors. Provides 30 minutes fire resistance when correctly installed.
Double Strip (15mm)
Wider intumescent for heavy fire doors. Required for FD60 doors and some heavy FD30 installations.
Combined Intumescent + Smoke Strip
Integrated product combining fire protection and smoke sealing in one strip. Cleaner installation but more expensive.
Where Do Fire Strips Fit?
- Fitted in the door edge — around top, sides and sometimes bottom of door
- Fitted in the frame — alternative option, runs around the frame rebate
- Both door and frame — some doors require strips on both for full protection
- Never painted over — paint reduces expansion effectiveness
How To Check Your Fire Door Strips
Every fire door in your London property should have its strips checked at least annually. Look for:
- Strips clearly visible in the door or frame groove
- No gaps, splits, breaks or missing sections
- No paint overspray reducing expansion
- Strips run the full length of the door edges
- Smoke seals intact and not crushed or flattened
⚠️ DIY Warning: Do not attempt to add intumescent strips to a non-certified door. Retrofitting strips to a standard door does NOT make it a fire door. A fire door must be a certified assembly — door leaf, frame, strips, hinges and hardware all tested together.
How Doorz Handles Fire Door Strips
Every certified fire door Doorz London installs comes with correctly specified intumescent strips and smoke seals already integrated. During your free survey we check existing doors for strip damage and advise on repair or replacement. All work comes with a compliance certificate.
Need Expert Help?
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More Expert Guides
- Fire Door Regulations London 2026
- How To Choose Door Hinges UK
- Door Handles For Internal Doors
- Fire Door Inspection London
- Door Fitters London
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The information on this page is provided as general guidance only and may contain errors or inaccuracies. Doorz London Ltd makes every effort to ensure the accuracy of content but cannot guarantee it is complete or up to date. UK building regulations, fire safety law and industry standards change regularly. Nothing on this website constitutes legal, professional or regulatory advice. Always consult a qualified professional for advice specific to your situation.
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