FD30 Fire Doors for a Loft Conversion: What the Rules Actually Say

Get a fire door wrong and it does nothing. It looks like a fire door, it passed as a fire door on the quote, and in a real fire it holds smoke and flame back no longer than an ordinary door. In one documented loft conversion, a contractor added untested timber to the bottom of six fire doors, the doors cracked, and a building inspector called the house potentially unsafe. This is the one part of a loft conversion where a cut corner stays invisible until the day it matters.

What an FD30 fire door actually is

FD30 means a doorset that holds back fire for 30 minutes when tested. The "FD" is the national fire-door class, the "30" is the minutes. That buys the people upstairs half an hour to get down a protected stair while the fire is contained behind the door. A loft conversion turns a two-storey house into three storeys, and the new top floor is further from the front door, so that half hour is the whole point of the fire strategy.

The part homeowners and even some builders miss is that FD30 is not a door you buy off a shelf and screw in. It is the complete installed assembly: the leaf (the slab of the door itself), a certified frame or lining, intumescent strips set into the edge, the right hinges, and gaps within tolerance. The door is tested as one unit. Swap a component for one that was not in the tested design, and the certificate no longer applies. A certified leaf hung in an ordinary softwood lining, with the strips left off or painted over, is not an FD30 door. It is an expensive ordinary door.

Two test routes give the same thing. The older British route tests to BS 476-22 and gives the "FD" class, so FD30. The European route tests to BS EN 1634-1 and classifies to BS EN 13501-2, giving an "E" rating, so E30. For a loft conversion they are equivalent labels for the same 30-minute performance. The "S" suffix, as in FD30S, means the door also restricts cold smoke leakage, which needs an extra seal.

When a loft conversion triggers fire doors

The rules sit in Approved Document B, Volume 1, which covers fire safety in dwellings. The trigger is height. When a conversion creates a new storey with its floor more than 4.5m above the ground outside, the new stair has to become a protected stairway: a stair boxed in by fire-resisting construction so that a fire in any room off it cannot fill the stair with smoke before people escape (Approved Document B, paragraph 2.5 and 2.21). A typical loft floor sits above 4.5m, so this bites on most loft conversions. A low bungalow conversion where the new floor is 4.5m or lower is treated differently, with escape windows instead.

Once the stair is a protected route, the walls around it have to resist fire (the document calls for REI 30 construction, meaning 30 minutes of load-bearing capacity, integrity and insulation), and the doors opening onto it have to be fire doors. Existing doors on the lower floors that open onto the stair have to be upgraded or replaced too, not just the new ones in the loft.

4.5m

The whole fire-door requirement hangs on one measurement: the height of the new floor above the ground outside. Above 4.5m and the new stair becomes a protected stairway, which pulls every habitable room door off the stair into scope. The 4.5m is measured to the floor level of the new storey, following the method in Approved Document B, Appendix D.

FD20, FD30 or FD30S: the real rule

Several loft-company guides say FD30 is required outright, and it pays to know what the actual document says. Approved Document B does not require FD30 on the stair doors of a house. Its minimum for a door forming part of the enclosure to a protected stairway in a single-family dwellinghouse is FD20 (E20), set out in Appendix C, Table C1, item 11(b). FD30S, the version with smoke seals, is required in a house only for a door between the dwelling and an integral garage, under item 11(a).

So why does everyone fit FD30? Mostly because FD20 is no longer a real option. The certified door makers stopped selling FD20 doors without intumescent seals, so an FD20 in practice is an FD30 with strips anyway. The British Woodworking Federation's Fire Door Alliance goes further and recommends always fitting a properly installed FD30 with intumescent seals as the minimum, even where the regulations only ask for FD20. On top of that, building control teams split on what they will accept: some, like Bath and North East Somerset, specify FD20 to the letter, while others, like Dudley, require FD30 outright. None of the council guidance reviewed asks for FD30S on the stair doors.

The practical takeaway: fit FD30 with intumescent strips everywhere the stair rule applies, fit FD30S with a self-closer on the garage-to-house door only, and before you order anything, email your building control body and ask which rating they will sign off. Getting that in writing costs nothing and settles the FD20-versus-FD30 argument before it starts.

External resource

Approved Document B, Fire safety, Volume 1: Dwellings

The free, official guidance behind the fire door rules for loft conversions. Section 2 covers loft conversions and protected stairways; Appendix C and Table C1 cover fire doorsets and the FD20, FD30 and FD30S ratings.

gov.uk

A forward note worth knowing: an amendment to Approved Document B takes effect on 2 September 2029 and removes the old BS 476-22 "FD" column from Table C1, leaving the minima expressed in minutes under the European test standards. Work that starts before then carries on under the current text, so FD30 remains the label you will see on doors for now.

Door types, sizes and finishes

The leaf is the part you choose for looks and budget. An FD30 leaf is heavier and thicker than an ordinary door, commonly 44mm thick, built around a solid core rather than a hollow one. That extra mass is the fire resistance, and it is why fire-door hinges and frames are specified more heavily. Standard UK door openings are catered for across the certified ranges, so the leaf you want almost always comes as an FD30 version.

Glazed fire doors come with a catch. The glass is not ordinary glass, and it is not interchangeable. It has to be a type listed on the door maker's own certification, fitted with the matching intumescent glazing gasket and beads. A fire-rated pane in the wrong bead, or ordinary toughened glass in a fire door, fails the whole assembly. If you want light into a dark landing, order the door glazed from the maker rather than asking a joiner to cut an aperture into a solid leaf on site.

The complete doorset, not just the leaf

Think of an FD30 door as a kit of parts that only works when every part matches the tested design.

The leaf carries a permanent label or a coloured plug set into the top or hinge edge. It shows the rating, the maker, the certification scheme (Certifire or BM TRADA Q-Mark are the common ones) and a certificate number. If a door has no label and no plug, you cannot prove its rating, and building control can reject a door it cannot trace to a certificate.

The frame or lining has to suit a fire door. Fire linings are thicker and denser than standard linings, which matters in a loft where openings are often tight: upgrading to a fire lining can mean a wider hole in the wall and some replastering. Reusing the old lining and just swapping the leaf is the single most common way the rating is lost.

The intumescent strips sit in a routed groove in the edge of the leaf or the frame, and in a fire they swell up to seal the gap around the door. Fit them every time, follow the door maker's instructions for the size and number, and never paint over them, because paint stops them swelling. Full detail on sizing and fitting is on the intumescent strip page.

The hinges have to survive the heat. Approved Document B, paragraph C10, asks only that the essential components of the hinge have a melting point of at least 800C, with no count or grade stated in the document. Trade practice is three CE-marked hinges per leaf, commonly to grade 13, with intumescent pads behind them. The door's certificate lists the hinges it was tested with, and that list takes precedence over any rule of thumb.

The latch matters more than people expect. The door has to be held shut to resist fire, so a working latch or lock that keeps the leaf closed against the stop is part of the assembly. A fire door standing ajar, or one with a broken latch, is not doing its job.

Self-closers are a separate question with a clear answer for houses. Approved Document B, paragraph C5(c), exempts fire doors within a dwellinghouse from the self-closing requirement, so the stair doors inside your house do not need closers. The door between the house and an integral garage is the exception and must self-close. Some councils, such as Eden, ask for rising-butt hinges on the stair doors instead, so check your local policy. The detail on closers is on the door self-closer page.

Gaps and fitting tolerances

Gaps are where good doors go bad. Approved Document B gives no gap figure itself, but the gov.uk fire door guidance is clear: the gap around the leaf should never be more than 4mm. In practice, aim for 2mm to 4mm at the head and down both sides, even all the way round. Too tight and the door binds and will not shut properly; too loose and the intumescent strip cannot bridge the gap when it swells.

The threshold gap at the bottom is different and follows the door maker's instructions. On a fire-only door it is commonly up to 8mm; where cold smoke seals are fitted it needs to be smaller, about 3mm to 4mm, so the drop seal or brush can close it. The "10mm rule" you sometimes hear is not a general limit; it is a threshold figure for a few specific fire-only assemblies, not something to apply to the perimeter.

How to check a fitted fire door

You can inspect a fire door yourself before building control does. Run through this on every door:

• The leaf has a visible label or a coloured plug in the top or hinge edge showing the rating and a certificate number.
• There are three CE-marked hinges, firmly fixed, ideally with intumescent pads behind them.
• The intumescent strip runs unbroken round the frame or leaf and has not been painted over or cut short.
• The gap at the head and sides is 2mm to 4mm, and the threshold gap matches the maker's instructions.
• The latch engages and holds the door firmly shut against the stop.
• Any glazing is the maker's listed glass in the correct beads, not ordinary glass.
• No letterplate, cat flap or air grille has been cut into the leaf unless it is a certified fire-rated one. Any aperture has to be covered by the door's certification.

How many fire doors you need

The rule is a counting exercise, not a guess. Every habitable room that opens onto the protected stair, on every storey, needs a fire door: bedrooms, living rooms, studies and, where the council includes it, the kitchen. Some councils, such as Dudley, also want a fire door at the head or foot of the new loft stair. Add the house-to-garage door on any house with an integral garage. Bathrooms and WCs without a fuel-burning appliance are generally left out, though councils vary, so get the list confirmed.

Work it through for a common case. A two-storey three-bed house being converted might have three bedroom doors and perhaps a bathroom off the first-floor landing, two to four room doors off the ground-floor hall, and the new loft-room or stair door. Strip out the bathrooms and you land at roughly five to nine fire doors, plus the garage door if there is one. One documented loft conversion needed six. The number climbs fast in a house with an open-plan ground floor, because new partitions and doors may be needed to box the stair back in.

What it costs and where to buy

The leaf is the biggest single choice, but it is only part of the cost. The strips, hinges and, on the garage door, a closer add to each opening, and then there is the labour to hang it.

A plain flush leaf is the cheapest way in. Moulded panel leaves at £105 – £125 suit a period house, and oak veneer at £160 – £250 gives a natural-wood finish. Wickes, Travis Perkins and the door specialists such as XL Joinery and Vicaima all stock FD30 ranges.

On top of the leaf, budget for a certified lining at £40 – £65, an intumescent fire-and-smoke strip pack at £9.00 – £11.19 per door from Toolstation or similar, and a set of three fire-rated hinges at £20 – £25. A closer, needed only on the garage door, is £20 – £30.

If you would rather buy the lot as one tested unit, a factory-assembled doorset (leaf, certified frame and seals) is £350 – £800 supply only, from the trade. It costs more than a leaf but removes the risk of mismatching parts on site.

For fitting, expect around that range per door to hang a certified leaf into an existing frame, including the strips and hinges. A new complete doorset fitted runs higher, £450 – £1,300 per opening, because you pay for the certified frame and the factory assembly as well as the labour, and the top of that band is where specified oak or glazed doors sit. London and the South East sit at the top. Putting a certified leaf into an old, uncertified lining is cheaper, but it may not preserve the rating, which is exactly the trap Approved Document B's "complete installed assembly" wording is there to close.

Where to buy FD30 fire door

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Upgrading existing doors instead of replacing them

Replacing every door is not the only route. Where an existing door has architectural or historical merit, Approved Document B, paragraph 2.22, allows retaining and, where needed, upgrading it rather than ripping it out. A solid, well-fitting period door can sometimes be brought up to 30 minutes with intumescent paint, paper or varnish systems applied to a detailed specification, plus intumescent strips and a check on the gaps. Bath and North East Somerset's guidance spells this out for retained doors.

This is worth it for Victorian panelled doors you want to keep, but it is fiddly and officer-dependent, and a thin hollow-core door will never make the grade. If the existing doors are modern hollow slabs, replacement is cheaper and more certain than any upgrade.

Where you will need this

A loft conversion is the most common reason a UK homeowner meets fire doors, but the same rules apply across other work that creates a third storey or a protected route. The fire strategy is specified together early: the stair enclosure, the FD30 doors, the escape windows and the interlinked alarms, so the openings are built right the first time. The doors themselves go in at second-fix carpentry once plastering is done, and building control checks every one at completion, which is where the self-inspection list above earns its keep.

The wider fire strategy connects to the loft staircase, which forms the protected route, and the interlinked smoke alarm system that has to cover it. Fire doors are one layer of a loft conversion's fire safety, and they only work alongside the enclosed stair and the alarms.

Common mistakes

The other recurring errors are smaller but just as costly at sign-off: painting over the intumescent strips so they cannot swell, leaving the strips off a door sold as "FD30 compatible", fitting ordinary hinges or only two hinges, cutting a non-rated cat flap or letterplate into the leaf, and ordering FD20 when the council has specified FD30 in writing. Every one of them is invisible until an inspector looks closely, and every one means a door comes back out. Confirm the rating with building control, buy the complete doorset or a matched set of parts, and fit it to the maker's instructions.