Fire door ratings explained: FD30, FD60 and the "S" suffix
Published · 5 min read
A fire door’s FD rating states how many minutes of fire resistance it provides when tested: FD30 gives 30 minutes, FD60 gives 60, with FD90 and FD120 for higher-risk locations. An "S" suffix (FD30S, FD60S) means the doorset also restricts cold smoke, which requires smoke seals and tighter gaps. Ratings are established by testing to BS 476-22 or BS EN 1634-1 and evidenced on site by certification labels, plugs or data plates.
What the numbers mean
The FD number is the doorset’s fire resistance in minutes under standard test conditions: FD30 and FD60 cover the vast majority of doors in commercial and residential buildings, while FD90 and FD120 appear where compartmentation demands more — high-hazard rooms, some protected shafts, and buildings with extended evacuation strategies. The rating belongs to the doorset as installed — leaf, frame, seals, glazing and ironmongery together — not to the leaf alone. A correctly rated leaf hung in the wrong frame, or with the wrong hinges, may achieve nothing like its nominal rating.
The S suffix: smoke as well as fire
Fire resistance and smoke control are different jobs. Intumescent seals expand in heat to hold back fire but do nothing against cold smoke early in a fire — which is what actually threatens escape routes first. Doors designated FD30S or FD60S must also restrict smoke leakage, which in practice means combined intumescent-and-smoke seals (or separate brush/fin seals) and much tighter gap tolerances, particularly at the threshold. Locations protecting means of escape — stair doors, corridor doors, flat entrance doors — typically need the S designation.
How a rating is proven
Ratings come from fire resistance testing to BS 476-22:1987 or BS EN 1634-1, and reach site as third-party certification: a colour-coded plug or label on the top edge of the leaf (BWF-Certifire, Q-Mark and similar schemes) or a data plate identifying the manufacturer and rating. On older doors with no marking, an experienced inspector may judge a solid-construction door to be a "notional" FD30 — a professional judgement that should be recorded as such, with the door’s construction described.
On site, the inspector’s question is two-fold: what rating does this location require, and what rating does the installed doorset demonstrably provide? AssessHub’s door inspection module records both — required and actual rating, certified and notional flags — alongside the eight-point condition check, so the report shows not just which doors are damaged but which are simply the wrong door for the job.
Frequently asked questions
Where are FD30 doors required?
Typical FD30 locations include doors onto protected corridors and stairways, flat entrance doors (usually FD30S), and doors to rooms opening onto escape routes. The requirement for any specific location comes from the building’s fire strategy and Approved Document B or BS 9999 guidance, not from the door itself.
Can I upgrade an existing door to a fire door?
Sometimes. Upgrade systems exist (intumescent papers, seals, replacement glazing), but the result is only as good as the evidence behind it — the whole doorset must be considered, and many upgrades are not certifiable. Replacement with a certified doorset is often the more defensible route for critical locations.
Is a fire door rating invalidated by damage?
Effectively yes. A rating assumes the doorset is in the tested condition — a damaged leaf, missing seal, over-planed edge or wrong hinges can reduce a nominal FD30 to little or nothing, which is why condition inspection matters as much as the label.
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