Approved Document K is the part of UK Building Regulations that governs staircase design — covering every dimension from step height to headroom clearance, and every element from handrail height to balustrade opening size. Whether you're designing a new staircase, replacing an existing one, or converting a loft, this guide sets out exactly what the regulations require and what the most common compliance failures look like in practice.
Bespoke modern staircase designed and installed by Continox — fully compliant with UK Building Regulations Approved Document K.
What Is Approved Document K?
Approved Document K — Protection from Falling, Collision and Impact — is the section of the UK Building Regulations that governs the design and construction of staircases, ramps, guards and vehicle barriers in buildings. It is issued by the Department for Levelling Up, Housing and Communities and sets out the technical requirements that must be met to satisfy Building Regulation K1 (stairs, ladders and ramps) and K3 (guarding).
Approved Document K applies to England and Wales. Scotland uses the Technical Handbooks (domestic and non-domestic), and Northern Ireland uses its own Technical Booklets — the requirements are broadly similar but differ in some dimensional specifics.
When Does It Apply?
Approved Document K applies whenever a new staircase is installed or an existing staircase is materially altered — including new builds, extensions, loft conversions, refurbishments and major renovations. It does not apply to like-for-like replacements on the same footprint where no material alteration is taking place, but Building Control should always be consulted if you are uncertain.
Three Categories of Staircase
Approved Document K distinguishes between three categories of residential staircase, each with different dimensional requirements:
Private Stairs
Serving a single dwelling — within a house or flat. The least restrictive dimensional requirements apply. Most domestic staircases fall into this category.
Common Stairs
Serving more than one dwelling — shared stairwells in apartment blocks, HMOs or converted houses. Stricter dimensions apply to accommodate more users and emergency egress.
Utility Stairs
Access to areas of limited use — loft hatches, plant rooms, occasional-use mezzanines. The most relaxed requirements apply but only in genuinely utilitarian contexts.
Building Control notification: Most new staircase installations require a Building Regulations application — either a Full Plans application or a Building Notice. Building Control will inspect the work at key stages and issue a completion certificate on satisfactory completion. This certificate is important for property sales and insurance purposes. For the full regulatory context, see our UK Staircase Building Regulations guide.
Residential Staircase Dimensions
The following table sets out the dimensional requirements for residential staircases under Approved Document K. Note the key differences between private stairs, common stairs and utility stairs — specifying private stair dimensions on a common stair is one of the most frequent compliance failures on residential conversion projects.
| Requirement | Private Stairs | Common Stairs | Utility Stairs |
|---|---|---|---|
| Max rise (per step) | 220mm | 190mm | 280mm |
| Min going (tread depth) | 220mm | 250mm | 150mm |
| 2R + G formula | 550–700mm | 550–700mm | — |
| Max pitch | 42° | 38° | No limit stated |
| Min headroom | 2000mm | 2000mm | 1900mm |
| Min width | No minimum stated | 1000mm clear | No minimum stated |
| Handrail height | 900–1000mm | 900–1000mm | 900–1000mm |
| Guarding height (landing) | 900mm (domestic) | 1100mm | 900mm |
| Max tapered step going | 220mm at centre | 250mm at centre | — |
Source: Approved Document K (2013 edition with 2016 amendments). Note: Scottish Technical Handbooks and Northern Ireland Technical Booklets have slightly different requirements.
The 2R + G formula: Approved Document K requires that the rise and going of each step satisfy the formula: 2 × Rise + Going = 550–700mm. This ensures a comfortable stride rhythm and prevents steps that are simultaneously too steep and too shallow. A staircase with a 180mm rise and a 220mm going gives: 2(180) + 220 = 580mm — within the required range. This formula applies to both private and common stairs.
Handrails & Balustrades: What the Regulations Require
Handrails and balustrades are governed by both Approved Document K (dimensional requirements) and BS 6180 (Barriers in and about Buildings — structural performance). The two work together: Part K tells you where they must be and how high; BS 6180 tells you how strong they must be.
When Is a Handrail Required?
A handrail is required on at least one side of a flight where the stair has more than two risers. Where the staircase is wider than 1000mm, handrails are required on both sides. Handrails should be at 900–1000mm above the pitch line of the stair and should be continuous across flights and landings.
When Is Guarding (Balustrade) Required?
Guarding is required at any level change of 600mm or more — including at the sides of flights, at landing edges, and at balcony or mezzanine edges. For domestic use, the minimum guarding height is 900mm at landings and 900mm at the sides of flights. For common stairs and external applications, the minimum is 1100mm.
The 100mm Sphere Rule
Approved Document K requires that no opening in a guarding system — whether between spindles, glass panels or other infill — should permit the passage of a 100mm diameter sphere. This is specifically intended to prevent the entrapment of small children's heads. For glass balustrade systems, the 100mm sphere rule applies to the gap at the base of the glass panel and any fixing gaps.
For full details on glass balustrade specifications, see our Glass Balustrade Regulations UK guide.
Open Tread Staircases: Specific Rules
Open riser staircases — where the risers are absent and the space between treads is open — are subject to the 100mm sphere rule in the same way as balustrades. The gap between treads must not permit the passage of a 100mm sphere. In practice, this means the vertical gap between the underside of one tread and the top of the next must not exceed 100mm.
For floating staircases with open risers, this requirement is often addressed by overlapping the treads slightly (nosing overhang) to reduce the effective vertical opening, or by using a narrow horizontal bar or fin between treads. The 100mm rule applies in the context of child safety — preventing a child's head from becoming trapped.
Nosing requirement: Approved Document K recommends (though does not require for private stairs) that treads have a nosing — a projection of 16–25mm beyond the face of the riser below. This improves tread depth perception and reduces the risk of the leading edge of the foot missing the step. For common stairs, a contrasting nosing is recommended to aid visibility.
Loft Conversion Staircases: Relaxed Requirements
Approved Document K recognises that loft conversions present particular spatial constraints and allows slightly relaxed dimensional requirements for staircases serving a single loft room in a dwelling where space is genuinely limited.
The relaxed requirements for loft conversion staircases allow: a maximum rise of 220mm (same as standard private stairs), a minimum going of 220mm, and — where space is genuinely constrained — a reduced minimum headroom of 1.8m at the centre of the stair and 1.9m at the sides, compared to the standard 2.0m requirement. These relaxations only apply where it can be demonstrated that a standard-compliant staircase cannot be accommodated within the existing structure.
Building Control confirmation required: The loft conversion relaxations are not automatic — they require Building Control to confirm that the reduced dimensions are justified by the spatial constraints. Do not assume reduced dimensions are acceptable without prior confirmation. A Continox design consultation will establish the most space-efficient compliant staircase layout for your loft conversion from the outset.
New Build vs Renovation: When Do Regulations Apply?
A common source of confusion is whether Building Regulations apply to staircase work in an existing property. The answer depends on what you are doing:
New build: Full compliance with Approved Document K is required. Building Regulations application needed. Building Control will inspect and issue a completion certificate.
Material alteration to existing staircase: Compliance required for the altered elements. If you are replacing a staircase that was previously non-compliant, the replacement must comply. Building Regulations application needed.
Like-for-like replacement on same footprint: Building Regulations may not apply, but confirmation from your local Building Control authority is strongly recommended before proceeding — particularly if the existing staircase is non-compliant.
Loft conversion: Full compliance required for the new staircase serving the loft, subject to the spatial relaxations described above. Building Regulations application required.
Completion certificates matter: A Building Regulations completion certificate is required for any staircase installation that needs a Building Regulations application. Without one, you may encounter difficulties when selling the property, remortgaging or making an insurance claim. Continox provides all structural documentation as standard — making Building Control sign-off straightforward.
5 Common Compliance Failures
The following mistakes are regularly identified by Building Control inspectors and result in rejection or required remediation. Avoiding them at the design stage saves significant cost and delay.
Applying Private Stair Dimensions to Common Stairs
Using a 220mm going or a 190mm rise on a staircase serving more than one dwelling. Common stairs require a minimum going of 250mm and a maximum rise of 190mm — significantly different from private stair requirements. This is the most common compliance failure on HMO and flat conversion projects.
Non-Uniform Rise and Going Within a Flight
All steps within a flight must have the same rise and the same going. Variation between steps — even by a few millimetres — is a compliance failure and a significant trip hazard. Building Control inspectors measure multiple steps on every flight. Ensure your staircase manufacturer controls fabrication tolerances carefully.
Open Risers Failing the 100mm Sphere Rule
The vertical gap between treads on an open riser staircase must not exceed 100mm. Many contemporary designs — particularly those with thick steel or oak treads — fail this requirement as-specified, requiring a nosing overhang or inter-tread bar to achieve compliance.
Incorrect Guarding Height for Application
Using 900mm guarding (domestic) on a common stair or external application that requires 1100mm. The distinction between domestic guarding (900mm) and common stair/external guarding (1100mm) is frequently confused — particularly on mixed-use developments and HMO conversions.
Headroom Failure on Loft Conversion Stairs
Failing to achieve the 2.0m minimum headroom on a loft conversion staircase without Building Control pre-approval for the relaxed 1.8m/1.9m requirement. Many loft conversion staircases are installed with insufficient headroom — creating both a safety risk and an unresolvable Building Regulations issue at the point of property sale.
Bespoke Staircases Designed to Comply
Continox designs, manufactures and installs bespoke residential staircases across the UK — with full compliance with Approved Document K as standard on every project. Our design process begins with precise site measurements and Building Control requirements confirmed before any design work proceeds. We provide photorealistic 3D visuals before manufacture so you can see exactly what your staircase will look like and confirm compliance.
All Continox staircase installations include free 3D design visuals, structural calculations, CAD drawings and compliance documentation. For a full cost breakdown see our Bespoke Staircase Cost UK guide. For design inspiration see our Modern Staircase Ideas UK guide.
UK Residential Staircase Regulations — FAQ
Common questions from homeowners, developers and architects about Approved Document K staircase requirements in the UK.
Part K Compliant From Day One
Free 3D design visuals, structural calculations included, fixed-price quotation after free site survey. Bespoke staircases from £7,900 — designed, manufactured and installed across the UK.
