Why the existing floors matter
Fire in a lower room must not immediately make the only stair unusable by somebody sleeping in the loft. Approved Document B therefore tells designers adding a storey above 4.5 metres to address the full extent of the escape route. The relevant measurement is the new floor's height above ground, not the roof ridge. [1]
For the normal protected-stair solution, the enclosure continues through the house towards a suitable final exit arrangement. An open-plan ground floor may need new partitions, or a properly designed alternative. An escape window in the new roof is not a substitute for that route in a typical three-storey house. [1] [2]
Approved Document B is statutory guidance describing ways to meet the functional regulations. Alternative designs need a reasoned demonstration of compliance; simply omitting part of the standard arrangement is not an alternative fire strategy. [1]
Fire doors and partitions
For the house-loft route in paragraph 2.21, the guidance specifies fire-resisting doors with a minimum E 20 classification and partitions with a minimum REI 30 classification. These are performance descriptions, not instructions to buy any door advertised as a 'loft fire door'. Existing doors may need upgrading as part of the escape-route design. [1]
A doorset's performance depends on the door, frame, seals where required, hardware and installation working together. The government's fire-safety FAQ explains why replacing the door leaf without considering the frame and supporting evidence is insufficient. The specification should identify each relevant doorway and its required performance. [3]
Do not assume that every door in the property needs identical work. The designer must identify the doors and partitions that perform a protective function in the proposed arrangement. Where existing doors have historic or architectural merit, paragraph 2.22 asks that retention and, where necessary, upgrading be investigated. [1]
Smoke alarms
Approved Document B calls for a fire detection and alarm system when a new habitable room is provided above the ground storey, with smoke alarms in the circulation spaces. Its general minimum is Grade D2, Category LD3, with circumstances in which a higher standard is appropriate. [1]
For the ordinary loft-conversion arrangement, Planning Portal explains the provision of mains-powered, interlinked smoke alarms at the relevant levels. The alarm layout, power supply and interconnection should be designed as a system, rather than leaving a single independent detector in the loft. [2]
Floors, beams and hidden openings
The new floor and supporting structure need the specified fire resistance. Service routes and openings must not undermine fire-resisting walls, floors or the stair enclosure. Review these details before ceilings and linings conceal them, and retain evidence of the installed construction. [1]
Flats and taller or more complex houses need their own assessment. In particular, Approved Document B separates the guidance for houses from the guidance for flats and their common parts. [1]
Changes already published for later use
The consolidated document includes separately marked amendments taking effect on 2 September 2029, removing the national fire-resistance classification route, subject to transition. Those future pages should not be mistaken for provisions already in force on 2 October 2026. Product and doorset specifications for later projects will need checking against the applicable edition. [1]