An escape window, or egress window, is a window big enough and low enough for someone trapped in a room by fire to climb out of. Approved Document B's own index files "emergency egress windows" under windows, so the two names mean the same thing. The rules on this page come from the current file, Approved Document B, Volume 1: Dwellings, the 2019 edition incorporating the 2020, 2022, 2025 and 2026 amendments, on a gov.uk publication page last updated on 16 September 2026. The escape paragraphs in Section 2 carry no amendment marks, so the recent changes, which deal with second stairs and evacuation lifts in taller buildings and national fire resistance classes, leave them as they were.
Two things are worth knowing before the detail. First, the law itself is one line: requirement B1 asks for "appropriate means of escape in case of fire from the building to a place of safety outside the building". The approved document sets out what "in ordinary circumstances, may be accepted as one way to comply", and it is the text FENSA's compliance guide and council building control pages are written from. Second, this guide is about replacing windows in an existing house. A new build, an extension or a loft conversion goes through building control, and the officer there, not an installer or a web page, is the person to ask about your plans. It sits alongside our other double glazing guides on the rules that apply when windows are replaced.
The size rule: Approved Document B paragraph 2.10
Paragraph 2.10 says windows providing emergency escape "should comply with all of the following", and its first item has three parts of its own. The area is the unobstructed openable area, which means the gap you could actually climb through with the window open as far as it goes, not the frame size on a quote.
| Test | What Approved Document B asks | Paragraph |
|---|---|---|
| Clear area | At least 0.33 m² of unobstructed openable area | 2.10a(i) |
| Height and width | At least 450 mm high and at least 450 mm wide. The route through may be at an angle rather than straight through | 2.10a(ii) |
| Height above the floor | Bottom of the openable area no more than 1,100 mm above the floor. No minimum is set | 2.10a(iii) |
| Where it leads | People escaping must be able to reach a place free from danger from fire. An enclosed courtyard or back garden with no way out except through other buildings must be longer than the height of the house, or of a rear extension if that is greater (Diagram 2.5) | 2.10b |
| Locks and stays | Locks, with or without removable keys, and opening stays with child-resistant release catches may be fitted | 2.10c |
| Staying open | The window must be capable of remaining open without being held | 2.10d |
Source: Approved Document B, Volume 1: Dwellings, paragraph 2.10 and Diagram 2.5. Flats use identical figures at paragraph 3.6.
Why "and" matters, and who writes "or"
FENSA's Guide to Compliance (version 2023.07), Richmond upon Thames Building Control's page on replacement windows and at least one window supplier state the rule as 450 mm high or450 mm wide. Approved Document B says "a minimum height of 450mm and a minimum width of 450mm", and so do the Welsh approved document at paragraph 3.8 and the Scottish Technical Handbook at clause 2.9.4. The difference is real. An opening 400 mm wide and 900 mm high gives 0.36 m², which passes the "or" wording and fails Approved Document B, because it is under 450 mm wide. Follow the approved document. FENSA's own worked figure only makes sense that way: if one side is at the 450 mm minimum, it says, the other needs to be at least 734 mm to reach 0.33 m². Richmond gives 733 mm for the same case; 0.33 divided by 0.45 is 0.733 m, so both are roundings of the same arithmetic.
No minimum height, and where the 800 mm comes from
Paragraph 2.10 sets a maximum height for the bottom of the opening and no minimum. A building control guide from Colchester and North Essex and a window supplier's page both put the bottom of an escape opening between 800 and 1,100 mm above the floor. The 800 mm is from Approved Document K, protection from falling, whose Diagram 3.1 gives an 800 mm guarding height at opening windows. It is a rule about falling out, not about escaping, and FENSA's guide treats restricting the window as an alternative to guarding it. Oldham Council's wording is the accurate one: no lower than 800 mm "unless precautions are taken to prevent falling risks". On a replacement, FENSA applies the same "no worse" test to falls as to escape. Where a window is less than 800 mm above the floor and the floor is more than 600 mm above the ground outside, a new window must be restricted or guarded if the old one was; if the old one was not, a restrictor is encouraged but not required.
Which rooms need an escape window
In a house in England the answer depends on the storey and on the stair. A habitable room is one used for living in. Approved Document B defines it to include a kitchen but not a bathroom, and paragraphs 2.1 and 2.2 then exclude kitchens by name.
| Where the room is | What it needs | Paragraph |
|---|---|---|
| Ground storey | Every habitable room except the kitchen either opens directly onto a hall leading to a final exit, or has an escape window or door | 2.1 |
| Upper storey no more than 4.5 m above ground, one stair | Every habitable room except the kitchen has an escape window or external door, or direct access to a protected stairway | 2.2 |
| Upper storey more than 4.5 m above ground | A protected stairway or an alternative escape route. Escape windows are not the route | 2.4 to 2.6 |
| Inner room, reached only through another room | Allowed if it is a kitchen, laundry or utility room, dressing room, bathroom, WC or shower room, or a room on a storey up to 4.5 m with an escape window | 2.11 |
| Basement with habitable rooms | An escape window or external door, or a protected stairway leading to a final exit | 2.16 |
| Two rooms side by side | May share one escape window if a door between them reaches it without passing through the stair enclosure, and each room has its own access to the stair | 2.3 |
Source: Approved Document B, Volume 1: Dwellings (2026 consolidated edition). Galleries (2.15) and rooms inside flats (3.15 to 3.17) follow the same pattern.
Four points trip people up. The 4.5 m is measured to the floor. Appendix A and Diagram D6 take the height of the floor of the storey above ground level on the lowest side of the building, not the height of the window sill. A landing is not a protected stairway.Paragraph 2.5a describes a stair separated by fire resisting construction (minimum REI 30) at all storeys; an ordinary open landing is not that, so an upstairs bedroom off it still needs its escape window, whatever one installer's guide says to the contrary. Open-plan kitchens are a grey area. FENSA's guide counts kitchen-dining and kitchen-living rooms as habitable rooms; Approved Document B excludes kitchens and does not deal with the open-plan case in paragraphs 2.1 and 2.2, so if yours is one, ask building control rather than assuming either way. One is enough.FENSA's guide: "There is no requirement to have more than one escape opening in a room."
The protected stairway option is also why a room with only fixed glazing is not automatically a breach, and why our guide to picture windows treats the escape casement as a question to settle for each room rather than a blanket rule.
Above 4.5 m, and loft conversions
Above 4.5 m, Approved Document B does not rely on escape windows. With one internal stair and one storey over 4.5 m, paragraph 2.5 asks for a protected stairway, or a top storey separated from the floors below by fire resisting construction with an alternative escape route to its own final exit. With two or more storeys over 4.5 m, paragraph 2.6 adds an alternative route from each storey more than 7.5 m up, or sprinklers throughout designed and installed to BS 9251. FENSA's guide says the same: above 4.5 m, fire escape windows "are not an appropriate means of escape".
That is why loft conversions are usually not escape window jobs, which is the reverse of what some guides say. Where a conversion creates a storey above 4.5 m, paragraph 2.21 asks for the full extent of the escape route to be addressed, with fire resisting doors (minimum E 20) and partitions (minimum REI 30), upgrading existing doors where necessary. Paragraph 2.23 gives an alternative: sprinkler protection to the open-plan areas, plus a fire resisting partition and door separating the ground storey from the floors above, with the door giving the loft room access to a first-storey escape window. On a typical two-storey house, then, a loft conversion is protected-stair work, and the loft room does not rely on its own escape window. An installer's guide that says building control will expect every habitable loft room to have a full escape window is wrong for that house. The exception is a bungalow loft, where the new storey is not above 4.5 m and the rooms fall under paragraph 2.2. Either way a loft conversion is a building control application, and the officer sets the route for your house.
Replacing an escape window: what the new one has to match
This is the question most homeowners actually have, and Approved Document B answers it in two short paragraphs headed "Replacement windows". Paragraph 2.18 says the work should comply with Parts K and L and that, when complete, the building should comply with the other parts "to at least the same level as before". The law behind that is regulation 4(3) of the Building Regulations 2010: the work must leave the building compliant or, where it did not comply, "no more unsatisfactory in relation to that requirement than before the work was carried out".
Paragraph 2.19 then deals with escape windows specifically. It applies where two things are both true: the existing window is in a position that would need an escape window in a new house, and it is big enough to be used for escape. Then the replacement should either be "sized to provide at least the same potential for escape" or, if the existing window was larger than required, the opening "can be reduced to the minimum described in paragraph 2.10". Nothing in Approved Document B requires an undersized escape window to be brought up to today's size.
| The old window | The replacement must | Source |
|---|---|---|
| Bigger than the 2.10 minimum | Meet at least the 2.10 minimum. It may be smaller than the old opening, but no smaller than that | ADB 2.19b; FENSA; Richmond Building Control |
| At the 2.10 minimum | Give at least the same potential for escape | ADB 2.19a |
| Below the 2.10 minimum | Be no worse on area, minimum dimension and height above the floor. Making it bigger is recommended, not required | ADB 2.18; regulation 4(3); FENSA |
| Any size, in Scotland | Meet the current standard: 0.33 m², 450 mm high and 450 mm wide, bottom no more than 1,100 mm up. Like for like may still be permitted on listed buildings and in conservation areas | Technical Handbook Domestic, April 2026, clauses 0.5.1 and 2.9.4 |
Sources: Approved Document B, Volume 1, paragraphs 2.18 and 2.19; Building Regulations 2010, regulation 4(3); FENSA Guide to Compliance v2023.07; Richmond upon Thames Building Control (updated 29 May 2026); Scottish Building Standards Technical Handbook, Domestic, April 2026.
Richmond upon Thames Building Control, in a page updated on 29 May 2026, puts the rule more plainly than anyone else: replacement windows should not make means of escape "any worse than before" or should meet the current requirements, "which ever is the lesser". Where the old windows fall short, it "would strongly recommend" taking the chance to fix it, while saying in terms that this is not a requirement of the regulations. FENSA's guide agrees, and adds that although reducing to the minimum is permitted, it recommends keeping as much escape opportunity as possible, for example by keeping more than one escape window in a room, particularly on different sides of the house.
One widely read source is stricter. LABC Front Door says an escape window can only be replaced "with a window with the same or bigger opening and the same type of hinges". That is safe advice, but it is not the rule: Approved Document B, the Welsh approved document, FENSA and Richmond all allow an oversized opening to come down to the minimum. Where "no worse" really bites is a change of style. If the old casement was an escape window big enough to climb through, a fixed pane in its place gives no escape potential at all, which paragraph 2.19 does not allow. Paragraph 2.20 adds that replacing windows may mean fitting cavity barriers around the opening.
Before the old window comes out, measure its clear opening with the sash fully open, and the height of the bottom of that opening above the floor. FENSA advises its installers to keep evidence such as survey or pre-installation photographs in case of a later inspection. Keep your own copy.
Ask for the clear opening in millimetres, window by window, not the frame size. A quote that says "egress hinges" has told you about a part. Only the measurement tells you whether the window passes.
Double Glazing Cost Calculator Team
Egress hinges: the usual way to get there, not the rule
Approved Document B says nothing about hinge type, opening angle, "egress hinges" or "easy clean hinges". The test is the measured opening. Hinges matter because a standard friction stay limits how far the sash swings and its arms sit in the opening, so the clear gap is smaller than the sash. Colchester and North Essex Building Control's guide puts it this way: "Some windows will not fully open to achieve these dimensions without installing proprietary escape hinges", so specify them. FENSA recommends "egress hinges and non-key locking handles" on windows identified as escape windows. Our casement windows guide covers the hinge types in more detail.
No angle is a rule, and makers disagree on the numbers. Securistyle lists its Defender Egress Easy Clean hinge at 80° in the 12-inch size and 90° in the 16-inch size. ERA says a standard friction stay opens "typically up to around 90 degrees" and an egress stay "typically beyond 90 degrees". A spares retailer says fire escape hinges open "to almost 90 degrees" when fitted to a window of the right width. Width is the other half: one supplier, Modern uPVC Windows, recommends a 600 mm pane width to achieve the clear 450 mm. That is one supplier's figure, not a standard. The way to settle it is to measure the opening, not to read the hinge packaging.
Two other details. LABC Front Door notes that an escape window can be two side-opening casements with no fixed centre stile, and a supplier describes a flying mullion that moves with the master casement to leave one clear opening, which helps where each casement alone is too narrow. And style is not fixed by the rules: LABC Front Door observes that escape windows "are generally hinged at the side rather than being tilt and turn or pivoting", but a tilt and turn window passes if its turn opening meets the three measurements and stays open unaided (paragraph 2.10d).
Swapping a worn hinge on its own is a repair, and repair is not building work: the Welsh approved document says so in terms, and FENSA's scope excludes it. So nobody inspects a hinge swap, which is the reason to be careful. Fit a standard stay where an egress stay was and you can shrink the opening with no one noticing. Replace egress hinges with egress hinges; our guide to adjusting window hinges covers the job, at £100 to £250 fitted.
Locks, keys and restrictors
Paragraph 2.10c allows "Locks (with or without removable keys) and opening stays (with child-resistant release catches)" on escape windows. Guides from a council, a fire safety consultancy and an installer that say an escape window must open without a key or tool are stricter than the approved document. FENSA recommends keyless handles, and says so as a recommendation: "Although the Approved Document allows for both keyed and non-keyed locking handles, it is recommended that the non-key option is used." A stay that needs a key to release sits awkwardly with the "child-resistant release catch" wording, and no source we found settles it; that is a question for building control.
On restrictors, FENSA says non-locking restrictors are advisable on escape windows, and that restrictors should limit the opening to 100 mm or less and be able to be disengaged. That 100 mm is FENSA's guidance on falls, not an escape window figure. In Scotland, clause 2.9.0 of the Technical Handbook says locking devices on escape windows should not prevent occupants escaping, and that permanent obstructions such as fixed security grilles should not be used.
Scotland and Wales
Walesuses its own approved document, the 2006 edition incorporating 2010, 2016 and 2020 amendments, with the same figures: paragraph 3.8 asks for at least 0.33 m², 450 mm high and 450 mm wide, and the bottom of the opening no more than 1,100 mm above the floor. The rooms rule (paragraphs 3.3 and 3.4) and the replacement rule (paragraph 3.19) match England's, except that Wales names Parts L and N where England names Parts K and L.
Scotlanddiffers in two ways. The sizes are the same, in clause 2.9.4 of the Technical Handbook, Domestic, April 2026 edition, but the rooms are framed differently: an escape window is needed in every apartment on an upper storey not more than 4.5 m above the ground, unless there is an alternative route out of it, and in every inner room on such a storey. An apartment is any room not used solely as a kitchen, store or utility room, and ground-floor apartments other than inner rooms do not need one. The bigger difference is replacements. Clause 0.5.1 says windows that are a complete replacement "are not considered to be a repair and have to meet the full requirements of the standards". A frame replacement needs no building warrant, but it is meant to meet the current standard, not just match the old window, though like for like may still be permitted on listed buildings and in conservation areas. Clause 2.9.4 also asks that where a conservatory sits below an escape window, its roof is considered for people lowering themselves onto it, while leaving the choice with the owner. Northern Ireland is not covered here.
Who is responsible, and what happens if it is wrong
Approved Document B's introduction lists those responsible for building work as including "agents, designers, builders, installers and the building owner". When a replacement is fitted by an installer registered with a competent person scheme, building control does not need to be notified. The installer must give the occupier a copy of the certificate, and notify building control, within 30 days of finishing (regulation 20(3)), and the certificate is "evidence (but not conclusive evidence)" that the work complies (regulation 20(5)). Our FENSA guide covers what that certificate is worth when you sell.
Nobody measures the opening on the day, but the check can come later. FENSA's guide says a non-conformity is levied on the installer if an installation turns out not to comply "even if weeks, months or years have elapsed", and that a disclaimer "cannot be recognised as an alternative to meeting building regulation compliance". Contravening the Building Regulations is an offence under section 35 of the Building Act 1984, and under section 36 the council can serve a notice requiring the owner to pull down or alter non-compliant work, up to 10 years after it was completed. If you fit the windows yourself, the building notice and inspection are yours; how to fit a double glazed window sets out the fees, and supply-only vs fully fitted weighs that route against a registered installer.
Where the common summaries go wrong
Much of what ranks for this subject is written by installers and consultancies, and a good deal of it is safe advice presented as law. Safe advice is fine; it just is not the rule, and it can cost you a window you did not need or talk you out of one you did.
| What you will read | What Approved Document B says |
|---|---|
| 450 mm high or 450 mm wide | Both: a minimum height of 450 mm and a minimum width of 450 mm (2.10a(ii)) |
| The bottom must be between 800 and 1,100 mm up | A maximum of 1,100 mm only. The 800 mm is Part K guarding |
| It must open without a key | Locks with or without removable keys are allowed (2.10c) |
| It must be side-hung, not top-hung | No hinge type or style. It must stay open without being held (2.10d) |
| Replace it with the same or bigger opening | An oversized opening may be reduced to the minimum (2.19b) |
| Kitchens count too | Habitable rooms excluding kitchens (2.1, 2.2) |
| A first-floor room off the landing needs no escape window | It does, unless it has direct access to a protected stairway (2.2b) |
| 4.5 m is measured to the window sill | To the floor of the storey (Appendix A, Diagram D6) |
| Every loft room needs an escape window | Above 4.5 m, a protected route instead (2.21 to 2.23) |
Claims taken from FENSA's Guide to Compliance, council building control pages and installer and consultancy guides ranking in September 2026. Research in lib/research/fire-escape-windows-2026.md.
Getting replacement windows quoted
The time to settle which windows are escape windows is at the survey, before the frames are made, because a made-to-measure window with the wrong opening is expensive to put right. To see what a set costs first, the casement window calculator prices it from the number of windows. For fitted prices on your own openings, with the escape windows identified and certified by a registered installer, tell us what you have and Leads 2 Trade will arrange quotes from installers covering your postcode.
Frequently asked questions
In England, Approved Document B, Volume 1, paragraph 2.10 asks for an unobstructed openable area of at least 0.33 m², at least 450 mm high and at least 450 mm wide, with the bottom of the openable area no more than 1,100 mm above the floor. All three tests apply at once. At the 450 mm minimum in one direction, the other needs to be about 734 mm to reach 0.33 m². Wales and Scotland use the same figures.
In a house in England with one stair, every habitable room except the kitchen on a storey no more than 4.5 m above ground needs either an escape window or another way out: on the ground floor, a door opening directly onto a hall that leads to an exit; upstairs, direct access to a protected stairway. Bathrooms are not habitable rooms. Above 4.5 m, Approved Document B relies on a protected stairway or an alternative route, not windows. One escape window per room is enough.
In England and Wales, only if the old one did. Approved Document B paragraph 2.19 says that where the existing window is in a room that would need an escape window in a new house, and is big enough to escape through, the replacement must give at least the same potential for escape, though an opening larger than needed may be reduced to the paragraph 2.10 minimum. If the old window was below the minimum, the new one must be no worse (paragraph 2.18 and regulation 4(3)). Improving it is recommended, not required. Scotland is stricter: a complete replacement has to meet the current standard.
No. Approved Document B sets the size of the unobstructed opening and says nothing about hinge type. Egress hinges are how most uPVC casements reach that size, which is why FENSA recommends them and a building control guide tells you to specify them. What counts is the measured clear opening with the window fully open, and makers' egress hinges open to different angles, so measure rather than trust the name of the part.
Yes. Paragraph 2.10c allows locks, with or without removable keys, and opening stays with child-resistant release catches. Guides that say an escape window must open without a key are stricter than Approved Document B. FENSA recommends keyless handles as good practice, not as the rule.
Not in Approved Document B, which sets only a maximum: the bottom of the openable area no more than 1,100 mm above the floor. The 800 mm figure some guides give as a lower limit comes from Approved Document K, which asks for guarding at opening windows below 800 mm to stop falls. FENSA's guide treats restricting the window as an alternative to guarding it, so a lower escape window is not a breach of Part B.
Usually not in the way people expect. Where a loft conversion creates a storey more than 4.5 m above ground, as it does on a typical two-storey house, Approved Document B paragraphs 2.21 to 2.23 ask for a protected escape route: fire resisting doors and partitions, or sprinklers plus a fire resisting partition and door that give the loft room access to a first-floor escape window. Escape windows count only up to 4.5 m. A bungalow loft, where the new storey stays below 4.5 m, is where escape windows apply.
Usually nobody on the day. A replacement fitted by an installer in a competent person scheme such as FENSA is self-certified, and the installer must give you the certificate within 30 days. FENSA can still levy a non-conformity on the installer years later, and the council can serve a notice to alter or remove non-compliant work for up to 10 years after completion. The building owner is among those responsible, so keep the certificate and photographs of the old window.