Summary

Staircase regulations in the UK are defined primarily by Approved Document K (Protection from falling, collision and impact), with additional references to Approved Document M (Accessibility) for certain building types. The regulations distinguish between private stairs (in a single dwelling), common stairs (in multi-unit buildings), and stairs in non-domestic buildings — each with different dimensional requirements.

Getting stairs wrong is one of the most consequential carpentry errors. A staircase that is out of regulation creates a falling hazard, will fail Building Control inspection, and may require complete removal and rebuild. The most common failures are inconsistent rise heights (particularly the first and last riser), inadequate headroom, and balustrading that does not pass the 100mm sphere test.

Material alterations — replacing an existing staircase, significantly altering the pitch, or adding a new staircase to a loft conversion — all require Building Regulations compliance and typically Building Control sign-off. Like-for-like replacement of treads, risers, and balustrades without changing the geometry falls into a grey area but should be discussed with Building Control if there is any doubt.

Key Facts

  • Maximum private stair rise: 220mm per step
  • Minimum private stair going: 220mm (measured as horizontal tread depth excluding nosing)
  • Rise + going: Should be between 550mm and 700mm (comfort formula: 2R + G = 550–700mm is a useful guide)
  • Minimum headroom: 2,000mm measured vertically from the pitch line to the underside of ceiling or soffit — 1,900mm permitted at the sloped ceiling edge only
  • Maximum pitch (angle): 42° for private stairs
  • Minimum width: No minimum in Part K for private stairs, but 900mm clear is standard good practice; 1,200mm for common stairs
  • Handrail height: 900mm minimum to 1,000mm maximum, measured vertically from the pitch line
  • Handrail both sides: Required where staircase width exceeds 1,000mm
  • Balustrade sphere test: No gap should allow a 100mm sphere to pass — prevents children's heads from getting trapped
  • Balustrade height (stair): 900mm minimum measured from pitch line
  • Balustrade height (landing): 900mm minimum for domestic; 1,100mm for common stairs and landings
  • Climbable design: Horizontal rails and ladder-like balustrades are prohibited — must not be easily climbable
  • Open risers: Permitted in private stairs if opening does not allow a 100mm sphere to pass
  • Nosing projection: Maximum 25mm — excessive nosings cause toe-catch trips
  • Winder treads: Minimum going of 50mm at the narrowest point, 220mm going at 270mm from the narrow end
  • Relevant Part: Approved Document K (2013 edition — verify for latest update)

Quick Reference Table

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Parameter Private Stair Common Stair Note
Max rise 220mm 180mm Per step
Min going 220mm 280mm Measured horizontal
Headroom 2,000mm 2,000mm Minimum at all points
Max pitch 42° 38° Measured to horizontal
Handrail height 900–1,000mm 900–1,000mm From pitch line
Balustrade (stair) 900mm 900mm From pitch line
Balustrade (landing) 900mm 1,100mm From landing level
Sphere gap 100mm max 100mm max Any opening
Min width No minimum 1,200mm Private: good practice 900mm
Rise (mm) Going (mm) Pitch (°) 2R+G (check 550–700)
175 250 34.9° 600 — OK
190 250 37.2° 630 — OK
200 250 38.7° 650 — OK
210 240 41.2° 660 — OK
220 220 45.0° 660 — FAIL (45° exceeds 42° max pitch)
220 240 42.5° 680 — OK (marginal pitch)
175 300 30.3° 650 — OK (comfortable)

Detailed Guidance

Calculating Rise and Going

Before ordering or building a staircase, the floor-to-floor height must be measured precisely. This is the total rise. Divide the total rise by a target riser height to find the number of risers.

Example: Floor to floor = 2,700mm

  • Target rise = 190mm
  • 2,700 ÷ 190 = 14.2 — round to 14 risers
  • Actual rise = 2,700 ÷ 14 = 192.9mm (rounds to 193mm)
  • Going target = 250mm (check 2×193 + 250 = 636 — within 550–700 range, acceptable)
  • Total stair run = 13 goings (one less than risers) × 250mm = 3,250mm

Critical rule: All risers must be the same height. The tolerance is ±5mm between adjacent risers and ±10mm between any two risers in the flight. Inconsistent risers are the most common cause of trips and staircase failures on inspection.

Headroom Check

Measure headroom from the pitch line (an imaginary line drawn across the nosings of all treads) vertically upward to the soffit or obstruction above. The minimum 2,000mm must be maintained at every point, including at the bottom nosing, at the top nosing, and at any mid-flight obstruction such as a hatch or structural beam.

In loft conversions where geometry is tight, the headroom can reduce to 1,900mm at the bottom of the stair (the area where a person would be standing at the foot) and at the side of the flight where ceiling height reduces — but the main travel path must maintain 2,000mm. Consult Building Control if in doubt.

Balustrade and Handrail

Materials: Any structurally adequate material is acceptable — timber, steel, glass, or composite. The structural requirement is that the balustrade can resist a horizontal load of 0.36 kN/m (approximately 36kg per metre) applied at the top rail — this is a fairly modest load but balusters fixed only with a couple of screws into softwood will not achieve it.

Post fixings: Newel posts must be fixed to structure, not just to the tread. Use a newel bolt (threaded rod through the tread and carriage) or fix the post directly to the trimmer joist. A newel post that rocks is a failing.

Baluster spacing (the 100mm rule): Space balusters at maximum 99mm clear gap. A quick method: cut a 100mm spacer block from offcuts and use it to set each baluster during installation.

Horizontal rails: Approved Document K prohibits balustrade that is "designed to be climbable." Horizontal rails are explicitly flagged as problematic — they act as a ladder for children. Vertical balusters are the safest option.

Glass panels: Where toughened glass panels are used, they must be Grade A safety glass (BS EN 12600 impact classification 1B1 or 1C1 [verify classification]). Fix panels in a U-channel or clamp system — never just rely on silicone adhesive.

Winder Stairs

Winder treads (tapered treads at turns) are permitted in private stairs but have additional requirements:

  • Minimum going at any point on the tread must not be less than 50mm
  • The going must be at least 220mm measured at 270mm from the narrow (inner) end
  • The walking line (where most people step) typically runs at 450–500mm from the narrow end — ensure going is comfortable at this point
  • Avoid more than 3 winders in succession if possible — three-winder quarter-turns are the norm for standard spiral-free loft conversions

Loft Conversion Stairs

Loft conversion stairs are the most frequently problematic due to space constraints. Key points:

  • Building Control must approve the design before work starts
  • The 42° maximum pitch applies — steeper "alternating tread" or "paddle" stairs are not compliant for a primary means of escape in a habitable loft conversion
  • If the loft room is used as a bedroom (or any habitable room), it must have a compliant means of escape — the stair IS the means of escape, so it must comply fully with Part K and Part B
  • Where an existing stair is being upgraded to serve a loft conversion, the existing stair must also comply — a steep original stair may need to be rebuilt

Frequently Asked Questions

Can I build a spiral staircase in a house?

Spiral staircases are generally not acceptable as the primary means of escape from habitable rooms under UK Building Regulations, as they cannot achieve the 2m headroom requirement and the going dimension at the walking line is typically too narrow. They may be acceptable as a secondary stair or for access to a non-habitable space (e.g. a small mezzanine study), but this should be agreed with Building Control before work starts.

Does replacing an existing staircase require Building Regulations approval?

It depends. A like-for-like replacement of treads, risers, or balusters (same geometry, same dimensions) is maintenance and does not require approval. If you are altering the rise, going, or geometry, or if the existing staircase serves a room created by a conversion, Building Regulations approval is required. Always check with Building Control if unsure.

What is the rule about handrails on both sides?

Part K requires a handrail on at least one side of a private stair. If the stair is wider than 1,000mm, a handrail is required on both sides. For stairs with an open side (no wall), a full balustrade must be provided on that side. Handrails must be continuous and graspable — a flat top rail on a balustrade is not an acceptable handrail unless it meets the graspability requirements (typically 45–50mm diameter circular or oval section preferred).

What is "pitch line" and why does it matter?

The pitch line is an imaginary straight line drawn across the nosings (front edges) of all treads. Headroom and handrail height are measured from this line rather than from the tread surface itself, because the pitch line represents the travel path. A handrail that starts at 900mm above the first tread surface will be shorter at the top of the flight if it does not follow the pitch line consistently — this is a common error that leads to non-compliance.

My customer wants an open-tread staircase — is that allowed?

Open treads (no risers) are permitted for private stairs, but any gap between treads must not allow a 100mm sphere to pass through. This means the gap cannot exceed 99mm. With a standard going of 250mm, the vertical gap from the underside of one tread to the top of the tread below will typically be less than 100mm, but always check the actual dimension for the specific design.

Regulations & Standards

  • Building Regulations Approved Document K (Protection from falling, collision and impact) — primary staircase regulation

  • Building Regulations Approved Document B (Fire safety) — means of escape via staircase

  • Building Regulations Approved Document M (Accessibility) — accessible stair design for common areas

  • BS 5395-1 (Stairs, ladders and walkways — code of practice for the design, construction and maintenance of straight stairs) — technical design standard

  • Building Regulations Approved Document K — GOV.UK — Official regulation document

  • TRADA — Timber Staircase Design Guide — Timber specification and structural guidance

  • NBS — Stair Design Guide — Technical specification reference

  • building control — When building control sign-off is needed

  • part b fire — Fire escape requirements for loft conversions

  • part m access — Accessibility requirements for stairs in certain building types

  • timber spans — Structural timber sizing