Component 01 of 10 · Structure

Door leaf

Fire-resisting leaf. The primary barrier.

The leaf is the mass of the fire door. The core chars slowly and holds the barrier against fire, while the other components keep it sealed, closed and in place. The rating belongs to the tested door assembly, not the leaf alone. This model is a timber leaf, the most common type in UK buildings. Fire doors are also made in steel, glass and composite, and hardware proven on timber does not transfer to them.

Key facts

Function: Holds back fire and smoke as the main body of the fire door
Specification: The fire resistance performance the door assembly is classified to, for example E 30 or EI 60, written as FD30 or FD60 in UK practice. Leaves are typically built at a nominal 44 mm for FD30 and 54 mm for FD60
Materials: Examples: particleboard, solid or laminated timber, flaxboard or mineral cores, usually lipped on the edges, commonly in hardwood
Critical tolerances: Per the manufacturer's evidence. Typically about 3 mm to the frame at head and jambs; trim only within the margin the fire door manufacturer's test evidence and specific guidance allow
Standards: Fire resistance evidenced by test to BS EN 1634-1, or for existing doors by earlier national BS 476 testing. Typically installed to BS 8214
Role in fire: Provides the fire resistance the door assembly is classified to
Where it sits: Hung within the frame on hinges the evidence covers

Compliance

The evidence covers the fire door for the specific configurations and applications it was tested in. Trimming past the permitted margin, cutting a new aperture or swapping a component could invalidate it. BS 8214 is the code of practice for fire door installation and is often what an installation is judged against.

Did you know

Timber does not give way suddenly. It chars inward from the exposed face, and the char layer can help insulate the sound timber beneath it. How long a particular leaf holds cannot be worked out from that: it comes from the test evidence for the complete construction.

On the model

Certification mark: Label or plug on the top edge
Engineered core: The mass that resists fire
Hardwood lipping: Protects and trues the edge
Closing edge: Operating gap set by the evidence
Bottom edge: Threshold gap per the evidence and any smoke control need

What inspectors check

Work through the checklist with the door closed, then in motion. Every line here is a recordable outcome for a Fire Door Inspector.

Locate the certification label or plug: usually the top edge, sometimes the hanging edge
Check perimeter gaps at head, jambs and threshold against the manufacturer's evidence
Look over both faces and all four edges for impact damage and splits
Sight down the leaf for bow or twist
Check for unauthorised holes, vents or apertures
Confirm lippings are intact and firmly bonded
Check the bottom edge for water damage and swelling

Common defects

Certification label or plug missing
Planed down beyond the permitted margin
Impact damage, splits or gouges in the face or edges
Holes or unfilled fixings through the leaf
Lippings damaged, loose or coming away
Leaf distorted, not sitting flush in the rebate
Water damage or swelling at the bottom edge
Unapproved apertures or surface fixings

Go deeper

Core types

The core decides the leaf's mass and what hardware can be fitted to it. It cannot be identified by looking at the face: only the evidence and the manufacturer's data tell you what is inside. Fixing types and lengths for any core follow the manufacturer's instructions. Whatever the core, it is the evidence for the complete construction that makes a fire door, not the material.

Solid particleboard: A dense, uniform board of bonded wood particles. Typically found in FD30 leaves.
Solid or laminated timber: Strips or laminates of timber bonded into a slab, including laminated veneer lumber. Typically chosen where the leaf carries heavier hardware.
Flaxboard and agrifibre: Compressed plant fibre bonded into a board. Typically lighter than particleboard for the same thickness.
Mineral core: Non-combustible mineral board. Typically found in higher-rated leaves and in many steel fire doors. Fixings need the provision the manufacturer specifies.
Graduated density core: Density engineered to vary through the thickness. Fixing lengths follow the manufacturer's instructions, which can differ from those for a uniform core.

How timber behaves in fire

Two things are worth understanding about timber and fire. Neither of them lets you predict a rating.

Charring from the exposed face: Timber exposed to fire converts to char from the outside in. The char layer is a poor conductor, so it can help insulate the sound timber beneath it.
Why the assembly is what is rated: How long a leaf holds is not a property of the timber alone. Facings, lippings, seals, the frame and the hardware all take part, so fire performance comes from the test or assessment evidence for the complete construction, not from the leaf's thickness or the density of its timber.
Calculations are a specialist job: The behaviour of timber in fire can be modelled, and the relevant standards set out how.Fire performance calculations, including charring assessments, must only be undertaken by appropriately competent specialists such as fire engineers or accredited test laboratories. A leaf's rating cannot be worked out on site from its thickness or its species.
Why thickness is nominal, not decorative: 44 mm and 54 mm are the sizes leaves are built to for FD30 and FD60, not measurements that prove a rating in reverse. Planing a leaf down removes material the test result depended on, and the leaf cannot tell you how much of its permitted margin has gone.

The mark in the edge is where the evidence trail starts: how to read a fire door’s certification.

Fire Door Anatomy is an introduction to fire doors, not the whole subject. Always defer to the fire door’s certification, its test evidence and a competent inspection.