Building Regs Part K Explained — Protection From Falling, Collision and Impact for UK Trades 2026

What Part K Covers — and Where It Applies

Approved Document K is the official guidance supporting Part K of Schedule 1 to the Building Regulations in England. It is split into several sections covering stairs, ladders and ramps; protection from falling (guarding); vehicle barriers and loading bays; protection against impact with glazing; protection from collision with open windows; and protection against impact from and trapping by doors. Achieving compliance with the guidance is one accepted way to satisfy the legal requirement — but the legal requirement is the regulation itself, not the document.

Part K applies in England. Wales has its own Approved Document K under the Welsh Building Regulations, which is broadly similar but maintained separately. Scotland does not use Part K at all — the equivalent protections sit under the Building (Scotland) Regulations and the Scottish Technical Handbooks, mainly Section 4 (Safety). Northern Ireland has its own Technical Booklet H covering stairs, ramps and guarding. The principles overlap heavily, but if you work across borders, check the document that applies in that country rather than assuming the English figures carry over.

Stairs, Ladders and Ramps

Stairs are the most common Part K issue trades meet, because almost every loft conversion, extension and refurbishment involves one. The geometry of a staircase is controlled so that it is comfortable and safe to climb and descend. The key dimensions for a private stair in a dwelling are a maximum rise of 220mm, a minimum going (the horizontal tread depth) of 220mm, and a maximum pitch of 42°. The rise and going must be consistent across the whole flight — mixing step heights is a classic cause of trips and an instant fail.

Headroom on the stair and on landings should be at least 2,000mm measured vertically above the pitch line. In loft conversions where the roofline makes full headroom impossible, the guidance allows a reduced headroom of 1,900mm at the centre of the stair width and 1,800mm at the edge — a concession that exists specifically because so many loft stairs sit under a sloping ceiling. Handrails are required on stairs, generally on at least one side where the flight is less than 1,000mm wide and on both sides where it is wider, set at a height of between 900mm and 1,000mm measured above the pitch line.

Ramps must not be steeper than the gradients set out in the guidance and need handrails where they rise above a certain height. Fixed ladders are only acceptable for access to a loft or similar space used intermittently by one person, not as the main route between storeys. If a client wants a space-saving or alternating-tread stair, those are permitted only in tightly defined circumstances — usually for access to a single room in a loft conversion — so confirm it with building control before you commit.

Guarding — The 100mm Sphere Rule

Wherever there is a change in level that people could fall from, Part K requires guarding: barriers, balustrades and railings to landings, balconies, stairs, the edges of raised floors and the sides of ramps. For stairs and landings inside a dwelling, the minimum guarding height is 900mm. For the edges of balconies, external balconies and edges of flat roofs with access, the guarding must be at least 1,100mm high. These figures are the headline numbers inspectors check first.

The most frequently failed rule is the gap test. In buildings that children under five could use — which in practice means almost all dwellings — guarding must be constructed so that a 100mm sphere cannot pass through any opening. This applies to the gaps between balusters, the gap below the bottom rail, and any open horizontal feature. The intent is to stop a small child's head passing through or a child climbing the guarding. Horizontal rails that a child could use as a ladder are discouraged for this reason, and many specifications use vertical balusters or glass panels instead. Guarding also has to resist the horizontal loads set out in the loading standard BS 6180 and the structural loading code, so a balustrade is not just about the gaps — it has to be strong enough not to give way when leaned on.

Balconies, Changes in Level and Replacement Balustrades

Balconies and Juliet balconies are firmly in Part K territory. A Juliet balcony — a glazed or railed barrier across a full-height opening with no floor projecting out — still needs guarding to 1,100mm and must satisfy the same 100mm sphere rule and loading requirements. Where a balcony floor projects out, the guarding around its edge must reach the balcony height and resist the relevant horizontal load. Any change in level that someone could fall from, including the edge of a raised patio door threshold, mezzanine or split-level floor, is assessed against the same principles.

Replacing a balustrade is one of the most common Part K triggers people overlook. Swapping a tired timber stair balustrade for a glass-and-steel system, or replacing balcony railings, brings the new guarding under current Part K standards — you cannot simply match the old height and gaps if they no longer comply. Inspectors regularly reject replacement balustrades that keep an old 850mm height or wide-gap design that was acceptable decades ago but is not now.

Protection Against Impact With Glazing

Part K's glazing section is where joiners, glaziers and door fitters get caught out. The rule is built around the idea of critical locations — areas of glazing where people are most likely to walk into the glass or fall against it, and where breakage would cause the worst injuries. In broad terms, the critical locations are glazing in doors and the side panels next to doors up to 1,500mm above floor level, and glazing in walls and partitions up to 800mm above floor level. These are the zones at body height where a stumble or push could put someone through the glass.

Glazing in a critical location must do one of the following: break safely (toughened or laminated safety glass that complies with the relevant glazing standard, so it crumbles or holds together rather than forming sharp shards), be robust enough that it is unlikely to break, be in small enough panes, or be permanently protected. In practice this means safety glass to the appropriate impact class is the standard answer for glazed doors, side screens, low-level windows, shower screens and internal glazed partitions. Using ordinary annealed float glass in a critical location is a serious and common failure.

Large uninterrupted areas of glass — full-height glazed doors and screens — also need to be made apparent so people do not walk into them. This is manifestation: a permanent marking, line, logo or pattern applied to the glass at the heights set out in the guidance so that the glazed surface is obvious. Frameless glass doors and big shopfront-style screens are the usual culprits. If the glass has features such as mullions, transoms or large handles that already make it visible, separate manifestation may not be needed, but a clear sheet of glass with nothing on it almost always will be.

Collision With Open Windows and Protection From Falling Down Stairs

Part K also deals with windows and openings that project into circulation routes. A window, rooflight or ventilator that opens outward or inward into a space where people pass — a corridor, an external walkway — must not create a collision hazard. Where the bottom of the opening is below 900mm, there is a risk of someone falling out, and guarding or restrictors come into play; where parts project into a route at head height, they must either be kept clear of the zone people walk through or be protected and made apparent. This is mostly a commercial and communal-building concern but applies to any project where opening lights sit over a path or landing.

The same guarding logic protects people from falling down a flight of stairs at the top landing and from falling off the open side of a stair. A continuous handrail and properly designed guarding to the stairwell void are not optional extras — they are the Part K features that stop the most serious domestic accidents, and they are checked on every stair sign-off.

Vehicle Barriers and Loading Bays

At the heavier end, Part K covers vehicle barriers to any floor, roof or ramp that vehicles can reach — the edges of car parks, raised forecourts and loading bays — and the edges of loading bays themselves. These barriers have to resist defined vehicle impact loads and reach specified heights so a vehicle cannot roll or be driven over the edge. For most domestic trades this rarely comes up, but if you work on commercial car parks, basement parking under flats, or any structure with a driveable edge above a drop, the vehicle barrier requirements and the impact loading apply and should be designed by an engineer rather than estimated on site.

When Part K Is Triggered

Part K compliance is required whenever you create or alter the features it governs. The usual triggers are:

• A new staircase in an extension, new build or reconfiguration — geometry, headroom, handrails and guarding all apply.
• A loft conversion — almost always involves a new stair under a sloping ceiling, plus guarding to the new landing and stairwell.
• Alterations to an existing stair — moving it, changing the rise and going, or opening up the void.
• Replacement balustrades and guarding — bringing a new barrier up to current height, gap and loading standards.
• New or replacement glazed doors, side screens and internal glazed partitions — safety glass in critical locations and manifestation on large panes.
• New balconies and Juliet balconies — guarding height, the sphere rule and loading.

Like-for-like replacement of a single window pane generally does not trigger a fresh Part K assessment, but anything that changes the geometry, the guarding or introduces glazing in a critical location usually does. When in doubt, treat it as notifiable and check.

How Part K Interacts With Building Control

Part K is not certified on its own — it is signed off as part of the wider building control process for the whole job. If the work needs a building control application (a full plans application or a building notice), the inspector will check the Part K features as part of their inspections and final sign-off, and the completion certificate covers Part K along with everything else. There is no separate Part K certificate.

You have two routes: notify your local authority building control, or use an approved inspector. Some glazing work can be self-certified under a competent person scheme by registered installers, which avoids a separate building control notice for that element — but the Part K safety-glazing and manifestation requirements still apply, and you remain responsible for getting them right. The practical point for trades is simple: build the stair, guarding or glazing to current Part K standards from the start, because an inspector who finds a non-compliant stair or balustrade at completion will withhold the certificate until it is corrected, and remedial work after the finishes are on is expensive.

Common Part K Failures Inspectors Pick Up

• Balustrade gaps too wide: openings that let a 100mm sphere pass — usually between balusters or under the bottom rail. The single most common rejection.
• Guarding too low: 850mm or 900mm guarding used on a balcony edge where 1,100mm is required, or replacement balustrades matched to a non-compliant old height.
• Missing or wrong-height handrails: no handrail on a flight, a handrail outside the 900mm to 1,000mm band, or none on the second side of a wide stair.
• Non-safety glass in critical locations: annealed float glass in door panels, side screens or low-level glazing instead of toughened or laminated safety glass.
• No manifestation: large frameless glazed doors and screens with no permanent marking at the required heights.
• Inadequate headroom: loft stairs that fall below even the relaxed 1,900mm and 1,800mm allowances.
• Inconsistent rise and going: a flight where the steps are not uniform, or a pitch over 42°.

Quick Reference: Part K Key Dimensions (Dwellings, England)

Figures relate to dwellings in England under Approved Document K. Confirm exact values against the current document and note that Wales, Scotland and Northern Ireland use their own equivalents.

Part K FAQ

Is Part K the same as working at height?

No. Working at height during the build is governed by separate health-and-safety rules and is about temporary protection for workers. Part K is about the permanent built features — stairs, guarding, glazing — that protect the people who use the finished building. They are entirely different regimes and you can comply with one while failing the other.

Does replacing a glazed door trigger Part K?

Yes. A new or replacement glazed door is glazing in a critical location, so the panes must be safety glass to the appropriate impact class, and large clear panels may need manifestation. Registered installers can self-certify under a competent person scheme, but the Part K requirements still have to be met.

Can I keep my old balustrade height when I replace it?

Not if it falls short of current standards. A replacement balustrade is treated as new guarding and must meet the relevant height, the 100mm sphere gap rule and the loading requirements. An old 850mm or wide-gap balustrade that predates current rules will usually be rejected if you reinstate it like-for-like.

Who signs off Part K?

Building control — either your local authority or an approved inspector — checks Part K as part of the overall inspection and completion certificate for the job. There is no standalone Part K certificate; it is covered within the wider sign-off.

Does Part K apply in Scotland?

Not by that name. Scotland uses the Building (Scotland) Regulations and the Scottish Technical Handbooks, mainly the Safety section, for the equivalent protections. Wales has its own Approved Document K and Northern Ireland uses Technical Booklet H. The principles are similar but check the document for the country you are working in.