Security and escape pull in opposite directions
A window that is hard to open from outside is also, in principle, harder to open from inside in an emergency. Fitting window locks is a standard security step, but a window can be the second way out of a home when the stairs are blocked by fire. This article summarises Approved Document B, volume 1 (dwellings), as published on GOV.UK in the edition that incorporates the 2020, 2022, 2025 and 2026 amendments and the forthcoming 2029 changes, together with London Fire Brigade advice on bedtime checks. The GOV.UK page for the document says it applies to England and was last updated on 16 September 2026. Wales, Scotland and Northern Ireland have their own building regulations, which are outside this article.
What kind of document this is
Approved Document B is statutory guidance to the Building Regulations 2010 on fire safety. It explains that the Building Regulations apply to building work as defined in regulation 3, and that those responsible for the work, including the building owner, may face prosecution in the magistrates’ court if the regulations are contravened. The guidance is written for building work, so it sets out what escape provisions are expected when a dwelling is built or altered.
When an escape window is needed
For the ground storey, the document says that all habitable rooms except kitchens should have either an opening directly onto a hall leading to a final exit, or an emergency escape window or door. For upper storeys that are a maximum of 4.5 metres above ground level and are served by one stair, all habitable rooms except kitchens should have either an emergency escape window or external door, or direct access to a protected stairway. Taller dwellinghouses have further provisions, including alternative escape routes or sprinklers.
The size and height rules
Paragraph 2.10 sets out the criteria for a window used for emergency escape. The window should have an unobstructed openable area of at least 0.33 square metres, with a minimum height of 450 millimetres and a minimum width of 450 millimetres, and the route through the window may be at an angle instead of straight through. The bottom of the openable area should be a maximum of 1,100 millimetres above the floor. People escaping should also be able to reach a place free from danger from fire, and the document says that courtyards or inaccessible back gardens should comply with its Diagram 2.5. The same paragraph says windows should be capable of remaining open without being held.
What the document says about locks
On locks, paragraph 2.10 states that locks, with or without removable keys, and opening stays with child-resistant release catches may be fitted to escape windows. The guidance therefore does not prohibit key-operated window locks on escape windows. It sets out the other criteria, such as the openable area and the requirement that the window can stay open, that the window must still meet. It does not say how a particular lock should be specified, so a homeowner or installer choosing a lock for a bedroom window should confirm with the building control body, or the manufacturer’s documentation, that the fitted product suits an escape window.
Why keys matter
A lock that needs a key only helps an escape if the key can be found quickly. London Fire Brigade’s bedtime checklist tells households to keep door and window keys where everyone they live with can find them, and to keep escape routes clear of anything that may slow an escape. That advice suits a household with young children, older relatives or visitors who may not know where a key is kept, and it should be settled before a fire, not during one.
- Agree one known place for keys, near the window or in a fixed spot in each bedroom.
- Make sure every occupant, including guests, is shown how the window and its lock operate.
- Check that the window can be opened wide enough to meet the size figures above once the lock is released.
- Avoid fixing grilles, bars or other fittings that reduce the unobstructed openable area of a window that is a room’s escape route.
Where these questions overlap with other guides
For new homes, the security requirements of Building Regulations Approved Document Q are covered in Approved Document Q: What Building Regulations Actually Require for New-Build Home Security in England. Fittings such as grilles and shutters are treated in Security Glazing, Window Film, Grilles and Shutters, and the overlap between security and fire safety in shared houses is set out in HMO Licensing and Fire Door Rules: Where Security and Fire Safety Overlap.
The bottom line
Approved Document B for England does not treat security and escape as mutually exclusive: it states that locks, with or without removable keys, may be fitted to escape windows, provided the window still has the required openable area, a bottom edge of the openable area no more than 1,100 millimetres above the floor and the ability to stay open unaided. What makes a locked window safe is the practice around it: keys that everyone in the household can find, occupants who know how to open the window and no permanent obstruction across an escape route. Anyone altering windows in England should check the building control position before work starts.
Sources
- GOV.UK, Ministry of Housing, Communities and Local Government, “Fire safety: Approved Document B”
- Ministry of Housing, Communities and Local Government, “Approved Document B (fire safety) volume 1: Dwellings, 2019 edition incorporating 2020, 2022, 2025 and 2026 amendments collated with 2029 amendments” (PDF)
- London Fire Brigade, “Bedtime checks”