Means of Escape: Protected Stairways, Inner Rooms & Building Regs Part B

Summary

Means of escape is a fundamental life-safety requirement, not a box-ticking exercise. The principles are straightforward: every occupant must be able to escape from any part of the building to a place of safety before fire and smoke make the escape route impassable. The design must assume that a fire could start in any room, and that the building is occupied at night when occupants are asleep.

For most simple two-storey houses, the existing layout with smoke alarms meets Part B without any additional work. The complexity arises with three-storey properties (including loft conversions), properties with open-plan layouts where the only stair exits through a kitchen, and properties with inner rooms (a room you can only get to through another room). These situations require careful design and attention to fire door specification, glazing limitations, and escape windows.

Builders and tradespeople most commonly encounter escape requirements during loft conversions, house extensions (particularly rear extensions that create open-plan layouts where the stair now opens into a kitchen), and property refurbishments where rooms are rearranged. Getting this wrong can delay building control approval and, in the worst case, result in dangerous situations.

Key Facts

• Approved Document B Volume 1 — dwellings; section 2 covers means of escape in dwellings
• Protected stairway — a staircase enclosed by fire-resisting construction (walls and ceiling 30 min min) with self-closing FD20S fire doors; provides a protected route from upper floors to the exit
• FD20S — 20-minute fire door with smoke seals; minimum for doors opening onto protected staircases in dwellings
• FD30S — 30-minute fire door with smoke seals; required where higher fire resistance is needed (e.g., between garage and dwelling, or flat front doors)
• Inner room — a room accessible only through another room (the access room); hazardous if the access room is a kitchen or garage where fire is more likely to start
• Escape window — minimum openable area 0.33m² (minimum 450mm high AND 450mm wide); cill height not more than 1.1m from floor; required for inner rooms and top-storey rooms in 3-storey houses where no protected stair exists
• Thumb-turn lock — escape windows must be openable from inside without a key; thumb-turn locking is acceptable
• Two-storey houses — typically do not need a protected staircase; relies on Grade D, Category LD2 smoke alarms giving advance warning; occupants must be able to get out before smoke fills the stair
• Three-storey houses — requires protected staircase from top floor to final exit; all doors to habitable rooms opening onto the stair must be FD20S; or alternative measures (sprinklers, AOVS)
• Sprinklers — can substitute for protected staircase in some cases; designed to BS EN 12845 or BS 9251
• Automatic Opening Vent (AOV) — smoke control at roof level of the stair; alternative to fully protecting all rooms with FD20S
• Open-plan layouts — where the ground floor stair exits through a kitchen, the kitchen must be separated with FD20S door, or the layout changed; a stair exiting directly into a kitchen on the ground floor of a 3-storey house presents an unacceptable risk
• Escape route travel distance — in a domestic dwelling, the horizontal travel distance from any point in an open-plan area to a protected stair or final exit door should not exceed 9m
• Corridor and landing width — minimum 750mm clear width for escape corridors; main stair minimum 800mm between strings

Quick Reference Table

Detailed Guidance

Protected Stairways — What They Require

A protected staircase is an enclosed route from the top floor to a final exit. The enclosure must provide:

• Walls: 30-minute fire resistance (FR30). Typically 100mm dense blockwork, or 100mm stud with 2 × 12.5mm plasterboard each side
• Ceiling: 30-minute fire resistance. Typically 12.5mm plasterboard on joists (or 2 × 12.5mm for higher spec)
• Doors: FD20S on all habitable rooms opening directly onto the stair. Self-closing devices (overhead door closers, spring hinges) are mandatory — propped-open fire doors are ineffective
• Glazing: any glazing in fire doors or walls forming the protected stair must be fire-rated. FD20S doors accept small vision panels with Georgian wired glass or fire-rated intumescent glass (e.g., Pyrodur, Contraflam). Large glazed areas are not acceptable.

What opens directly onto the stair?

• Bedroom doors — must be FD20S
• Living room and dining room doors opening directly onto the hall/stair — must be FD20S
• Bathroom doors — FD20S required if opening directly onto stair
• Kitchen doors — FD20S required; additional risk because kitchen is a fire origin room

What does NOT need to be FD20S?

• Cupboard doors within the stair enclosure (if the cupboard is small and contains no gas or electrical hazards)
• Loft hatch — must be fire-resisting if it opens into the protected stair

Loft Conversions and Three-Storey Rules

This is where Part B creates the most work in domestic building. Converting a loft to create a third storey triggers the protected staircase requirement even if the house previously had none.

Options:

Option A: Full protected staircase — enclose the entire stair from ground floor to loft with FD20S doors and 30-minute walls. Works well but means every door from hallway to rooms on all floors must become an FD20S with a self-closer. Clients often resist this because self-closing doors are inconvenient. Retrospectively, many installed fire doors end up propped open — making them useless.

Option B: Alternative escape from loft room only — provide escape windows from the loft room (meeting the 0.33m² / 450mm × 450mm requirements) AND protect only the route from the ground floor to the loft stair head with FD20S. This is sometimes possible depending on layout.

Option C: Sprinkler system — installing a domestic sprinkler system to BS 9251 can allow a relaxation of the fire door requirements. Increasingly used in residential loft conversions, especially where the self-closing fire door requirement is impractical.

Building control officers have some discretion in applying Part B to existing dwellings — the principle is "equivalent level of safety" rather than exact compliance with every clause. Get pre-application advice from building control early in the design process.

Inner Rooms

An inner room is a room you can only access through another room (the "access room"). Examples:

• A study or dressing room behind a bedroom (bedroom is the access room)
• A bedroom above a garage where the only access is through the garage
• A room reached through a kitchen or garage — both high fire risk access rooms

If the access room is a kitchen, garage, or any room with significant fuel load or ignition risk, the inner room arrangement is unacceptable without remediation. Solutions:

1. Provide an escape window from the inner room (minimum 0.33m² opening, 450mm × 450mm min, cill ≤1.1m)
2. Provide a separate door from the inner room directly to the hall or protected route
3. Rearrange the layout to eliminate the inner room arrangement

If the access room is a low-risk room (e.g., a dining room), an inner room arrangement may be acceptable if the inner room has an escape window. Confirm with building control.

Escape Windows — Specification and Installation

Escape windows must be:

• Minimum openable area: 0.33m² clear opening
• Minimum dimensions: 450mm high AND 450mm wide (both dimensions must be met)
• Maximum cill height: 1.1m from floor level
• Opening mechanism: must be openable from inside without a key; thumb-turn or handle locking is acceptable; key-locking is not (in an emergency, keys are dropped/lost)
• Opening direction: casement or top-hung preferred; bottom-hung windows do not provide an adequate opening for egress

For roof windows (Velux or similar) in loft conversions, a centre-pivot or top-hung window opened fully provides an adequate escape opening if it meets the above dimensions. Check manufacturer data — not all roof windows have sufficient clear opening.

Where a window is above the ground floor, escape is typically via a fire escape ladder (retained in the room or permanently fixed externally) or by rescue from an external platform. Building control will assess the specific arrangement.

Fire Door Specification and Installation

FD20S (20-minute fire door with smoke seals):

• Typically 44mm solid core timber door (fire-rated to BS 476 Part 22 or BS EN 1634-1)
• Intumescent strips in the door edge (activate at ~180°C, sealing the gap) plus cold smoke seals (compress to seal gap at ambient temperature)
• Three hinges (certification typically requires this — two-hinged doors are rejected)
• Self-closing device (overhead closer or hydraulic floor spring)
• Maximum gap: 3mm at sides and top, 8mm at threshold

FD30S: same as above but tested to 30 minutes. Required for flat entrance doors, between garage and habitable space, and some commercial situations.

Do not hang fire doors on standard loose-pin butt hinges — fire doors require CE-marked fire-rated hinges.

Frequently Asked Questions

My client wants to remove the hallway wall to create open-plan living — is this allowed?

It depends on the house layout and storeys. In a 3-storey house, removing the hallway wall would typically eliminate the protected staircase, which is unacceptable without compensatory measures. In a 2-storey house, an open-plan ground floor is generally acceptable with appropriate smoke detection (Grade D, LD2), as long as the stair doesn't exit through a kitchen. Always check with building control before removing internal walls on escape routes.

Do all bedroom doors on the first floor of a 3-storey house need to be FD20S?

Yes, in a three-storey house with a protected staircase, all habitable room doors (bedrooms, living rooms, bathrooms) that open directly onto the protected stair and landing must be FD20S with self-closers. This is one of the most contentious requirements — clients resist the self-closing mechanism especially for bedroom doors. Using a door retainer (hold-open device linked to the smoke alarm, which releases on alarm activation) is an alternative but must be correctly specified and maintained.

Can I use glass panels in fire doors for a loft conversion?

Yes, with the right glass. Standard float glass will crack and fall out in a fire. Acceptable glazing options: CE-marked fire-rated glass (e.g., Pyrodur, Contraflam, Georgian wired glass for shorter durations). The glass must be within the certification of the door set. Do not glaze a fire door with standard glass and assume it is compliant.

Does Part B apply to renovations as well as new build?

Part B applies to new build and to "material alterations" — works that would unacceptably affect existing compliance with the Building Regs. If you're converting a loft, extending, or making significant structural alterations, Part B applies to the whole stair/escape route, not just the new work. This can mean upgrading fire doors throughout the house as part of a loft conversion — an unexpected cost that should be included in quotes.

Regulations & Standards

• Building Regulations Approved Document B Volume 1 — means of escape in dwellings, Section 2

• BS 476 Part 22 — fire tests on building materials and structures (door sets)

• BS EN 1634-1 — fire resistance and smoke control tests for door and shutter assemblies

• BS 9251:2021 — fire sprinkler systems for domestic and residential occupancies

• BS EN 1154 — building hardware; controlled door closing devices

• PD 7974-6 — the application of fire safety engineering principles; human behaviour in fire

• GOV.UK — Approved Document B Volume 1 — dwellings fire safety

• LABC — Loft Conversion Fire Safety — practical guidance

• DCLG Fire Door Guidance — fire door specification

• Fire Door Alliance — inspection and certification guidance

• smoke alarms — alarm grades, categories, and interlink requirements

• fire stopping — fire stopping at penetrations and cavities

• loft conversions — three-storey fire requirements for loft conversions

• building control — building control for fire safety compliance