Approved Document K: UK Stairs, Guarding & Barriers Guide

Summary

Approved Document K (Protection from falling, collision, and impact) is the building regulation most relevant to carpenters, joiners, and builders who construct or alter stairs, balconies, landings, and guarding systems. Falling is one of the leading causes of serious injury in UK homes, and Part K is designed to reduce these risks through prescriptive dimensional requirements for stairs and barriers.

The current edition is Approved Document K 2013, in effect from 6 April 2013. It amalgamated the former Approved Document N (glazing safety) and some overlapping guidance from Approved Document M, and updated the standards references for safe breaking and for barrier loads. No amendments have been issued since. Part K must be read alongside Part M (Access and use) for accessible design, and Part B (Fire safety) for fire escape staircases.

For tradespeople, Part K is most commonly triggered by: building a new staircase, replacing or repairing a domestic staircase, fitting a new balustrade or guarding to a balcony or landing, and designing raised platforms or mezzanine floors.

Key Facts

• Stair dimensions — private stair (domestic), ADK Table 1.1:
  • Rise: minimum 150mm, maximum 220mm
  • Going: minimum 220mm, maximum 300mm
  • The relationship 2R + G must be between 550mm and 700mm (where R = rise, G = going)
  • Maximum pitch: 42° (this limit applies to private stairs only — ADK sets no explicit maximum pitch for the other categories)
  • Minimum headroom: 2000mm (2m) measured vertically from the pitch line. Loft conversion exception: where 2m cannot be achieved, ADK Diagram 1.4 allows 1.9m at the centre of the stair width reducing to 1.8m at the side
• Other ADK stair categories: utility stair (rise 150–190mm, going 250–400mm) and general access stair (rise 150–170mm, going 250–400mm). "Common stair" is not an ADK term — a common stair in a block of flats is a general access stair
• Stair width: ADK sets no minimum width for private stairs generally. For buildings other than dwellings: 1200mm minimum between enclosing walls/strings, 1000mm between handrails. Where means of escape applies, refer to Approved Document B
• Handrails (ADK 1.34): Provide a handrail on at least one side; on both sides if the stair is 1000mm or wider. Top of the handrail 900mm to 1000mm above the pitch line or floor. The handrail may form the top of a guarding if the heights match
• Length of flights (ADK 1.17): If stairs have more than 36 risers in consecutive flights, provide at least one change of direction between flights of at least 30° — not simply a straight landing. For buildings other than dwellings, maximum risers between landings are 16 (utility) and 12 (general access, exceptionally 16)
• Guarding height (ADK Diagram 3.1) — single family dwellings:
  • Stairs, landings, ramps and the edges of internal floors: 900mm for all these elements
  • External balconies, including Juliette balconies, and edges of roof: 1100mm
  • (Other building types: 900mm for flights, 1100mm elsewhere. Do not apply 1100mm to internal landings in a house — 900mm is the ADK figure)
• When guarding is required: in dwellings, where there is a drop of more than 600mm. In buildings other than dwellings, where there are two or more risers, or a drop of 380mm if not part of a stair
• Baluster spacing: In buildings that may be used by children under five, guarding must prevent a 100mm sphere from passing through any opening. This is the standard specified for dwellings in practice, and applies to the whole guarding — including the gap between the floor and the bottom rail
• No horizontal rails: ADK 3.3(b) — where children under five may use the building, guarding must be constructed to avoid horizontal rails that can be climbed. Vertical balusters or other non-climbable infill preferred
• Glazing in critical locations (ADK Diagram 5.1): in doors and door side panels (within 300mm of the door), glazing up to 1500mm above floor level; in walls, partitions and windows away from doors, glazing below 800mm above floor level. Glazing in a critical location must satisfy Class 3 of BS EN 12600 (or Class C of BS 6206). For a pane in a door or door side panel wider than 900mm, Class 2 of BS EN 12600 (or Class B of BS 6206) is required. Alternatives to safe-breaking glass are robust glazing, small panes, or permanent protection
• Part K and conservation areas / listed buildings: ADK applies in principle, but exemptions may be granted where achieving dimensional compliance would harm historic fabric. Discuss with Building Control and the LPA/Historic England before any stair work in listed buildings

Quick Reference Table

Detailed Guidance

Stair Geometry Calculations

The key formula for stair design is: 2R + G = 550–700mm, where R is the rise (vertical height of each step) and G is the going (horizontal depth of each step, measured from nosing to nosing).

Examples:

Finding rise and going from floor-to-floor height:

1. Measure the floor-to-floor height (e.g., 2700mm)
2. Divide by maximum rise (220mm): 2700 ÷ 220 = 12.27 → 13 risers minimum
3. Calculate actual rise: 2700 ÷ 13 = 207.7mm (round to 208mm)
4. Calculate going from formula: G = 600 − 2 × 208 = 184mm — too small. Try 14 risers
5. 14 risers: rise = 2700 ÷ 14 = 192.9mm (193mm). G = 600 − (2 × 193) = 214mm — marginal
6. Use G = 250mm for comfort: 2R + G = 386 + 250 = 636mm — compliant and comfortable

All risers must be the same height (tolerance ±5mm between any two risers in the same flight). Tapered risers at the bottom (common in historic staircases) are addressed in the non-standard stair guidance.

All goings must be the same depth — except for winding stairs (see below).

Winding Stairs (Tapered Treads)

Quarter-turn stairs and spiral stairs use tapered treads that are wider at the outer edge than the inner. Part K allows this with conditions:

• The minimum tread width at the narrow end must be at least 50mm
• Stairs less than 1m wide: measure the going at the centre of the tread. It must meet the minimum for the stair category (220mm private, 250mm utility or general access)
• Stairs 1m or wider: measure the going at 270mm in from each end of the tread. The going at the inner 270mm line must not be less than the category minimum, and the going at the outer 270mm line must not exceed the category maximum
• Consecutive tapered treads must use the same going (ADK 1.26)
• Where a flight mixes straight and tapered treads, the going of the tapered treads must not be less than the going of the straight treads (ADK 1.27)
• Spiral and helical stairs are designed to BS 5395-2, not to the tapered-tread rules above

Winding stairs reduce the effective going on the inside of the turn and must be laid out carefully. A full-size setting-out board or CAD layout is recommended before cutting strings and treads.

Handrails

A handrail provides a grippable support surface along the stair. Requirements:

• Profile (ADK Diagram 1.13): Must be grippable. A circular handrail of 32mm to 50mm diameter, or a non-circular handrail 50mm wide and 39mm deep with rounded edges of at least 15mm radius. Clearance from the wall 50–75mm, and at least 50mm below the rail. Flat plate handrails are not grippable and do not comply
• Height: 900mm to 1000mm above the pitch line or floor (measured vertically from the nosing line to the top of the handrail)
• Both sides: required where the stair is 1000mm or wider
• Continuity: In buildings other than dwellings, the handrail must be continuous along the flights and landings, extending at least 300mm beyond the top and bottom nosings, and finished so clothing cannot catch. In dwellings, returns to the newel post or wall are good practice for the same reason
• Projection: Handrails must not project into an access route

Material: Timber, steel, chrome, stainless steel — any structural material. Chrome tubular steel is very common for open-tread stairs; check the diameter falls within the 32–50mm grippable range. Timber handrails must be a profile that is grippable — a standard architrave moulding is not compliant.

Guarding (Balustrades)

In a dwelling, guarding is required at any open edge with a drop of more than 600mm. (In buildings other than dwellings the trigger is lower: two or more risers, or a 380mm drop where not part of a stair.) The purpose is to prevent people from falling.

Height requirements in a single family dwelling (ADK Diagram 3.1):

• Alongside a stair flight: minimum 900mm above the pitch line (not 900mm above the tread — above the line connecting the stair nosings)
• On an internal landing, or at the edge of an internal floor: minimum 900mm above the floor surface. This is a common point of confusion — 1100mm is not the ADK figure for internal landings in a house
• On an external balcony, including a Juliette balcony, or at a roof edge: minimum 1100mm

In residential, institutional, educational, office, public and retail buildings the figures are 900mm for flights and 1100mm everywhere else.

Baluster spacing (100mm sphere rule): No opening in the guarding (including the gap between the bottom rail and the floor, and between any balusters, spindles, or infill panels) may allow a 100mm sphere to pass through. In practice:

• Vertical balusters: maximum 100mm clear gap (typically 95–98mm centres to be safe)
• Toughened glass panels: the glass itself is a continuous barrier — check the gap at the fixing point between panels
• Open balustrade with horizontal rails: check that no 100mm sphere can pass between rails at any height. A small child could squeeze between horizontal rails — a common legacy issue in pre-2013 installations

Climbability: ADK 3.3(b) requires that in a building that may be used by children under five, guarding is constructed so children cannot readily climb it — in practice, avoid horizontal rails. Vertical balusters are preferred. Check with the client whether this is a concern.

Structural load: ADK 3.2(c) requires guarding to resist, as a minimum, the loads given in BS EN 1991-1-1 with its UK National Annex and PD 6688-1-1. For domestic and residential areas that works out at a 0.36 kN/m horizontal line load at the top of the guarding; balconies and areas with crowd loading are substantially higher (0.74 kN/m upwards). Most standard baluster systems are designed to meet these loads — confirm with the manufacturer's structural data. Further guidance on barriers and infill panels is in BS 6180.

Glazed Balustrades

Structural glass balustrades (toughened or laminated glass infill panels, or bolted glass panels with no top rail) are increasingly common in contemporary domestic settings. Requirements:

• Glass must be laminated toughened safety glass (17.5mm laminate — 8.8.4 or 10.10.4 — is the common domestic specification for a frameless system; the required build-up depends on the load case and fixing method, not a fixed minimum in ADK)
• Fixings must be engineered for the load — bolt fixings must be designed by a structural engineer
• The glass supplier must provide a structural certificate confirming compliance with BS 6180 (guarding) and the loads from BS EN 1991-1-1 with its UK National Annex and PD 6688-1-1
• All glass edges must be polished (no sharp edges)
• An obscure silicone bead at the base of each panel must not be the primary structural fixing — the glass must be clamped or bolted

Frameless glass balustrades are notifiable as structural glazing — Building Control will typically require a structural engineer's calculation.

Vehicle Barriers

Requirement K3 covers barriers to prevent vehicles from falling off the edges of car parks, ramps, and elevated driveways that form part of a building. For domestic use, this is most relevant for driveways that slope down to a lower level or basement garages.

ADK Diagram 4.2 sets minimum barrier heights, not load application points: at least 375mm at a floor or roof edge, and at least 610mm at a ramp edge. The barrier must resist the loads given in BS EN 1991-1-1 with its UK National Annex and PD 6688-1-1 — these are derived from vehicle mass, speed and the deflection of the car and barrier, so the design force is not a single fixed figure. Any wall, parapet or balustrade may serve as the barrier. This almost always requires a structural engineer's design for the barrier and its fixings.

Frequently Asked Questions

My customer's existing stair has a rise of 240mm. It was built legally in the 1970s. Does it need to be replaced?

No. Part K does not require the retrospective upgrading of staircases that were compliant with the regulations at the time of construction. The 240mm rise was compliant under pre-1991 standards. However, if the staircase is being materially replaced (new treads, strings, and newel posts — effectively a new stair), the replacement must comply with current Part K. If only repairs are being made (replacing a couple of treads), like-for-like replacement is acceptable.

How do I achieve 1100mm guarding on a balcony where the existing newel post is only 900mm?

First check the location: 1100mm applies to external balconies and roof edges. If this is an internal landing in a house, 900mm is the ADK figure and the existing newel may already comply. For a genuine external balcony, the options are: (a) Replace the newel post with a taller one and extend the balusters; (b) Add an extension post or cap fitting to the existing newel; (c) Install a top rail extension system above the existing rail. Ensure structural continuity — the guarding must still resist the design lateral load at its full 1100mm height. Adding a thin timber cap on top of an existing post that is not structurally connected is not compliant.

Can I use glass in a balustrade that's next to a stairs?

Yes — safety glazing is required for any glass in a critical location. ADK defines those as glazing in doors and door side panels up to 1500mm above floor level, and glazing in walls, partitions and windows below 800mm above floor level. Glass used as guarding to a change of level is also covered. The glazing must satisfy Class 3 of BS EN 12600 (or Class C of BS 6206) — Class 2 / Class B for door and side panes wider than 900mm. Toughened glass (single pane) breaks into small granules and is acceptable. Laminated glass (stays in place when broken) is preferred for balustrades because it continues to provide a barrier even after breakage.

Regulations & Standards

• Approved Document K, 2013 edition — Protection from falling, collision and impact. In effect from 6 April 2013; it amalgamated the former Approved Document N (glazing safety). No later amendments have been issued — this remains the current edition

• BS EN 1991-1-1 with its UK National Annex, and PD 6688-1-1 — the loads that guarding and vehicle barriers must resist (referenced directly by ADK 3.2 and 4.2)

• BS 6180 — Barriers in and about buildings: code of practice (guarding design and infill panels)

• BS 5395-1 — Stairs: code of practice for the design of stairs with straight flights and winders

• BS 5395-2 — Stairs: code of practice for the design of helical and spiral stairs

• BS EN 12600 / BS 6206 — Glass in building: pendulum test and classification (safety glazing)

• BS 8300 — Design of accessible and inclusive built environments (complements Part M/K for accessible stairs)

• GOV.UK — Approved Document K — Full text of the 2013 edition

• TRADA Timber Stair Design Guidance — Stair geometry and structural guidance for timber stairs

• NHBC Standards Chapter 6.9 — Guarding — NHBC interpretation of Part K for new-build houses

• staircase construction — Staircase construction sequence and joint types

• part m access — Access and use requirements for accessible stairs and handrails

• part b fire — Fire escape staircase requirements

• structural engineer — When to commission a structural engineer for balustrades and platforms