Vertigo Interiors / Guides

Open Plan Kitchen Fire Regulations: What Passes in 2026

Open plan kitchen fire regulations are the single most common reason a London open-plan scheme gets redrawn late. The structural question, whether the wall can come out, is usually solvable. The fire question, whether anyone can still get out of the house once it has, is the one that changes the plan.

This guide sets out how building control assesses an open-plan ground floor in England, what the numbers are, and where the line falls between a two-storey house and a three-storey one.

What actually governs it

The legal requirement is Part B of the Building Regulations. Approved Document B volume 1 covers dwellings and is the guidance most building control bodies work from. It is guidance, not law, which matters: you are allowed to meet Part B another way if you can demonstrate it, usually through a fire engineer's report.

The current version is the 2019 edition incorporating amendments up to 2026, with further 2029 amendments already collated into the published document. The most recent update, on 16 September 2026, added guidance on second staircases and evacuation lifts in taller residential buildings, so it does not touch houses, but it is a reminder that this document moves and that a 2019 PDF saved on someone's desktop is not current.

The inner room problem, in one paragraph

An inner room is a room whose only way out is through another room. Knock the wall between a kitchen and a living room and you have usually created one: to leave the living room you now walk through the kitchen, which is the room statistically most likely to be on fire. Building control will not accept that unless there is a second way out or the risk is controlled another way. That single principle explains almost every open-plan fire decision.

Two routes to a compliant open plan ground floor Two storey house Escape window in every first floor habitable room 0.33 m2 min openable area 450 mm min each way cill max 1100 mm above floor Three storeys or more Protected stairway required 30 min fire resisting enclosure, FD30 doors to habitable rooms Open plan usually needs suppression to BS 9251 Both: interlinked smoke alarms throughout, a heat alarm in the kitchen, mains powered with battery backup. A fire engineer's report can justify an alternative approach where the standard guidance does not fit. Graphic by Vertigo Interiors. Every figure appears, sourced, in the text.
The two standard compliance routes. Every figure shown is set out in the text below.

Two-storey houses: usually yes

In a standard two-storey house, a fully open-plan ground floor is normally acceptable provided every habitable room on the first floor has an escape window or direct access to a protected stair. That is the trade: the ground floor can be open because people upstairs can get out of a window if the stair is smoke-logged.

The escape window specification in Approved Document B is precise:

  • Minimum unobstructed openable area of 0.33 square metres.
  • Minimum 450mm high and 450mm wide, and the route through may be at an angle rather than straight.
  • The bottom of the openable area no more than 1100mm above the floor.
  • The window must stay open without being held, and any lock or stay must have a child-resistant release that can be operated without a key in an emergency.

This is where period London properties catch people out. A Victorian sash with a deep cill can fail the 1100mm rule even though it is a large window, and a replacement casement with a chunky frame can fail the clear opening test even though the aperture looks right. Measure the clear opening, not the hole in the wall. Our guide to fire escape window regulations goes through the measurement properly.

Three storeys and above: the hard case

Once a house has three storeys, including a loft conversion that adds one, a protected stairway becomes mandatory. The stair has to be enclosed in construction giving at least 30 minutes of fire resistance, with FD30 fire doors to every habitable room opening onto it, running to a final exit.

That is fundamentally at odds with an open-plan ground floor, because an open plan by definition puts the bottom of the stair into the same space as the kitchen. Three routes out of it:

  1. Keep the kitchen separate. Enclose the stair and the hall, and accept a kitchen behind a door. Cheapest and least popular.
  2. Fit suppression. A domestic sprinkler system designed and installed to BS 9251, or a water mist system to BS 8458, covering the open-plan space. Building control commonly accepts an open-plan ground floor on this basis, though some will still want the kitchen separated or a short fire engineer's report supporting a kitchen inside the space.
  3. Engineer it. A fire engineer's assessment justifying a specific layout, which is the route for anything unusual: a basement, a very deep plan, a listed building where doors cannot be added.

Retrofitting a mist system is generally less disruptive than sprinklers in an existing house, because the pipework is smaller, which is why it comes up often on London refurbishments. Either way it is a cost to budget at the design stage, not a detail to discover at inspection. Our loft conversion building regulations guide covers what adding a storey triggers.

Flats are a different regime

If you are opening up a flat rather than a house, the guidance is different again and generally stricter, because you are inside a larger building with a shared escape strategy. Open-plan flat layouts normally require suppression and specific limits on travel distance within the flat. In a leasehold flat you will also need the freeholder's consent: see licence to alter.

Alarms, which everyone forgets

Whatever route you take, the alarm system has to be upgraded. In practice that means interlinked, mains-powered detectors with battery backup: smoke alarms in the circulation spaces on each storey and a heat alarm, not a smoke alarm, in the kitchen. A smoke alarm in an open-plan kitchen will go off every time someone grills bacon, and an alarm that gets disabled protects nobody. Where the kitchen is open to the living space, the detection layout needs thinking about rather than defaulting.

Three design decisions that make compliance easier

  • Do not put the hob between the seating and the exit. Even where the layout is technically acceptable, positioning the cooking zone off the escape route rather than across it makes the case far easier to argue and is simply better design.
  • Keep a lobby if you can. A small hall with a door, even a glazed one, at the foot of the stair preserves the protected route and often saves the whole suppression cost. A frameless glazed screen with a fire-rated door can do this without killing the open feel.
  • Decide before you demolish. Adding sprinkler pipework or a fire-rated screen after the plaster is on costs several times what it costs before.

Getting it signed off

Building control approval is mandatory for this work even though planning permission usually is not, unless the property is listed or in a conservation area and the work affects the exterior. Involve your building control body, whether the local authority or a registered building control approver, at design stage rather than at first inspection. A ten minute conversation about the fire strategy before the drawings are issued is the cheapest part of the project.

For the wider picture of what a London renovation triggers, see our guide to building regulations for London renovations, and for the structural half of the same job, removing a load-bearing wall. If you are still at the layout stage, how to design an open-plan kitchen diner covers the design decisions, and Vertigo Interiors works through the fire strategy alongside the plan rather than after it.

Frequently asked questions

Do I need building regulations approval to make my ground floor open plan?

Yes. Removing internal walls and changing the escape route is building control work even when planning permission is not required. Planning only comes into it if the property is listed or the work affects the exterior in a conservation area.

What is the inner room problem in an open plan kitchen?

An inner room is a room you can only leave by walking through another room. Opening a living room into a kitchen usually creates one, because the escape route now passes through the kitchen, which is the room most likely to be the source of a fire. Building control will require a second escape route or another control measure.

What size does a fire escape window have to be?

Approved Document B asks for an unobstructed openable area of at least 0.33 square metres, at least 450mm high and 450mm wide, with the bottom of the openable area no more than 1100mm above the floor. The window must stay open unaided and any lock or stay must have a child-resistant release.

Do I need sprinklers for an open plan kitchen?

Not in a standard two storey house, where escape windows upstairs normally suffice. In a house of three or more storeys, including one created by a loft conversion, an open plan ground floor usually needs a domestic sprinkler system to BS 9251 or a water mist system to BS 8458, and some building control bodies will also want a fire engineer's report if the kitchen sits inside the open space.

Does a loft conversion change the rules for my open plan kitchen?

Yes, significantly. Adding a third storey triggers the requirement for a protected stairway enclosed in 30 minute fire resisting construction with FD30 doors. An existing open plan ground floor may have to be enclosed or fitted with suppression to stay compliant.

Can I have a smoke alarm in an open plan kitchen?

You need a heat alarm in the kitchen area rather than a smoke alarm, interlinked with the smoke alarms in the circulation spaces and mains powered with battery backup. A smoke alarm over a hob triggers on cooking and ends up being disabled, which defeats the point.

Sources