Why does a loft conversion change the escape rules?
Approved Document B sets different escape rules for storeys up to 4.5 m above ground and storeys above it. A loft room on a typical two-storey London house sits above that line, so the whole escape route has to be upgraded, not just the new floor.
On the ground and first floors of a house, the guidance accepts an emergency escape window as an alternative to a protected stair. Above 4.5 m it does not. The approach changes from escaping out of a window to protecting the route down through the house, so the stair itself becomes the escape route and has to be kept free of smoke and fire long enough for everyone to get out.
That is why a loft conversion is rarely just a loft job. Building control will want to see work on the first floor landing, the ground floor hall and the doors off both. For the full scope of the regulations, see our Part B glossary entry.
What does Approved Document B require at each height?
The requirement steps up at 4.5 m and again at 7.5 m above ground.
| Storey height above ground | What habitable rooms need | Approved Document B Vol 1 |
|---|
| Ground storey | An opening onto a hall leading to a final exit, or an emergency escape window or door | Paragraph 2.1 |
| Upper storey up to 4.5 m | An emergency escape window or external door, or direct access to a protected stairway | Paragraph 2.2 |
| One storey more than 4.5 m | A protected stairway (minimum REI 30) at all storeys, to a final exit or to two separated ground-level final exits | Paragraph 2.5 |
| Two or more storeys more than 4.5 m | As above, plus an alternative escape route from each storey above 7.5 m, or sprinklers throughout to BS 9251 | Paragraph 2.6 |
Source: Approved Document B Volume 1, Dwellings, 2019 edition incorporating 2020, 2022 and 2025 amendments, section 2, retrieved 12 September 2026. Kitchens are excluded from the habitable room requirements in paragraphs 2.1 and 2.2.
Most loft conversions on London terraces and semis fall into the third row: one new storey above 4.5 m. A house that already has a second floor, or a basement conversion combined with a loft, can reach the fourth row, where the 7.5 m test comes in.
What is a protected stairway?
A stair separated from the rest of the house by fire resisting construction of at least REI 30 at every storey, with fire resisting doors to the rooms that open onto it, leading to a final exit.
Paragraph 2.21 of Approved Document B deals with loft conversions directly. Where a conversion adds a storey above 4.5 m, the full extent of the escape route has to be addressed, and fire resisting doors of at least E 20 and partitions of at least REI 30 have to be provided, including upgrading existing doors where necessary.
| Element of the escape route | Minimum standard |
|---|
| Walls and partitions enclosing the stair | Fire resisting, REI 30 |
| Doors from habitable rooms onto the stair | Fire resisting, E 20 |
| Above the stair enclosure | Cavity barriers or a fire resisting ceiling, EI 30 |
| Where the stair ends | A final exit, or two ground-level final exits separated by REI 30 construction and E 20 fire doorsets |
| Smoke alarms | At least Grade D2 Category LD3 to BS 5839-6, mains operated with a standby supply |
Source: Approved Document B Volume 1, paragraphs 1.1, 1.2, 1.4, 2.5 and 2.21, retrieved 12 September 2026.
In a Victorian terrace, the stair usually already runs up a hall along the party wall, which helps. The weak points are almost always the same: panelled doors to the front and back reception rooms, a glazed door to the kitchen, and an open-plan ground floor where a previous owner took the hall wall out. Each one has to be dealt with, because the protection is only as good as its weakest opening.
Where an existing door has historical or architectural merit, paragraph 2.22 says the possibility of keeping it, and upgrading it where needed, should be investigated before replacement. That is worth raising with building control early on a period house.
What if the ground floor is open plan?
You either rebuild an enclosure around the escape route or follow the alternative approach in paragraph 2.23, which relies on sprinklers.
Many London houses now have the stair rising out of a knocked-through kitchen and living space. Paragraph 2.21 notes that new partitions should enclose the escape route where the layout is open plan. If that would undo the reason for buying the house, paragraph 2.23 sets out an alternative that must meet all of the following:
- Sprinkler protection to the open-plan areas.
- A fire resisting partition (minimum REI 30) and door (minimum E 20) separating the ground storey from the upper storeys, and that door must allow people in the loft room to reach a first storey escape window.
- Cooking facilities separated from the open-plan area by fire resisting construction (minimum REI 30).
The sprinkler route adds cost and a water supply question, and the separation at the foot of the first-floor stair still has to be designed. It is a legitimate option, but it is not a way of avoiding fire resisting construction altogether.
When do escape windows still matter?
On storeys up to 4.5 m, and as part of the open-plan alternative, where the first floor escape window becomes the fallback for people coming down from the loft.
| Emergency escape window, paragraph 2.10 | Requirement |
|---|
| Unobstructed openable area | At least 0.33 m² |
| Opening height and width | At least 450 mm high and at least 450 mm wide (the route through may be at an angle) |
| Bottom of the openable area | No more than 1100 mm above the floor |
| Fittings | Locks and child-resistant opening stays are allowed; the window must stay open without being held |
Source: Approved Document B Volume 1, paragraph 2.10, retrieved 12 September 2026.
A 450 mm by 450 mm opening gives only 0.2025 m², so a window that meets both minimum dimensions can still fail the 0.33 m² area test. Check all three numbers together. Paragraph 2.3 also allows two rooms to share one escape window, provided a door between them gives access to it without passing through the stair enclosure and both rooms have their own access to the stair.
Escape also has to lead somewhere. Where a window drops into an enclosed back garden with no way out except through other buildings, paragraph 2.10 and Diagram 2.5 say the garden must be longer than the height of the house above ground or, where there is a rear extension, its height, whichever is greater. That catches some short London yards.
How does the loft stair itself fit the escape route?
The new flight has to meet Approved Document K for safe use as well as sitting inside the protected route.
Headroom is the usual pinch point under a pitched roof. Approved Document K asks for 2.0 m of headroom over a stair, but for loft conversions where that is not possible it accepts 1.9 m at the centre of the stair falling to 1.8 m at the side of half the stair width. The new stair normally lands on the first floor landing inside the enclosure, so the loft room door at the top becomes one more opening that must meet the E 20 standard.
| Loft stair check | Figure | Source |
|---|
| Headroom, standard | 2.0 m | Approved Document K, paragraph 1.13 |
| Headroom, loft conversion where 2.0 m is impossible | 1.9 m at the centre, 1.8 m at the side of half the width | Approved Document K, Diagram 1.4 |
Source: Approved Document K (2013 edition), retrieved 12 September 2026.
What goes on the building regulations drawings?
A fire strategy that building control can check in one read: the enclosure, every fire door, the alarms and the final exit.
On our loft conversion drawings, the ground, first and loft floor plans mark the protected stairway, label each door with its fire rating, show the mains-linked smoke alarm positions and note any cavity barriers above the enclosure. Where a scheme relies on the sprinkler alternative, the plans say so and show the separation. That is what a building control officer checks against Part B, and it is what a builder prices from.
A loft conversion drawing package with us starts at £1,225, and a separate building regulations set starts at £840, as listed on our pricing page. For a detailed specification of the whole house, see our building regulations drawings service, or request a fixed quote for your loft conversion.
Written by Benyamen Shaukat, Technical Architect & Platform Founder. Fact-checked against Approved Document B Volume 1 (Dwellings), sections 1 and 2, and Approved Document K.
