Spiral Staircases: Sizes, Building Regs & Cost

Spiral staircases are among the most space-efficient internal stair options available: they can fit within a floor plan as compact as 1.2–1.6 m diameter, making them popular for loft conversions, mezzanines, and secondary access routes. They are also a genuine interior feature in their own right, with steel, timber, and glass options to suit most styles of home.

The key thing to understand before specifying a spiral stair is where Building Regulations place restrictions on their use. Getting this right at design stage avoids wasted expenditure later.

Sizes: What Are the Standard Diameters?

Spiral staircases are typically described by their overall (external) diameter. Kits are most commonly available in the following sizes:

The “clear walking width” is measured from the central pole to the inner face of the handrail. Tread depth still has to meet the minimum going: Approved Document K measures the going of a tapered tread at the centre of the tread where the flight is under 1 m wide, and 270 mm in from each end where it is 1 m or wider.¹

Building Regulations

Spiral staircases in England must meet Part K of the Building Regulations, and its guidance, Approved Document K (Protection from Falling, Collision and Impact), at paragraph 1.28 simply says to design spiral and helical stairs in accordance with BS 5395-2, the code of practice for helical and spiral stairs.¹ BS 5395-2 was published in 1984 and BSI still lists it as current.² The key Approved Document K points:

As a primary staircase (i.e., the only way between floors for habitable rooms), a spiral stair must meet all standard stair requirements:

• Rise: 150 mm minimum, 220 mm maximum per step (Table 1.1, private stair)¹
• Going: 220 mm minimum, 300 mm maximum¹
• Rise and going relationship: twice the rise plus the going between 550 mm and 700 mm, and a maximum pitch of 42°¹
• Headroom: minimum 2 m clear throughout¹
• Handrail height: 900–1,000 mm above the pitch line or floor¹
• Balustrade openings: a 100 mm sphere must not be able to pass through¹
• Width: Approved Document K sets no minimum width for a private stair. The only width figure it gives for a dwelling is 900 mm, and that applies to a flight in the entrance storey on a severely sloping plot.¹

Width still matters for a spiral: makers describe BS 5395-2 as setting clear widths by category of use, even though Approved Document K sets none. One UK maker says a spiral used as the main stair in a home needs a diameter of about 1,900 mm to give an 800 mm clear tread width.³ Another puts the smallest diameter for a primary spiral at 1,800–1,900 mm, depending on the model’s centre column.⁴ Bath and North East Somerset building control expects most spiral stairs to need an outside diameter of 1.3 m to 1.8 m just to meet the rise, going and headroom rules.⁵ Always confirm compliance with the supplier before purchasing.

As a secondary staircase (e.g., access to a single room like a study or craft room, where a separate primary stair exists), Building Control may accept a spiral with a smaller diameter and slightly relaxed tread depths. Discuss with your local authority building control (LABC) or a registered building control approver before assuming this applies to your project.

Loft conversions get one relaxation and it is only on headroom: where there is not enough space for the full 2 m, Approved Document K accepts 1.9 m at the centre of the stair falling to 1.8 m at the edge (paragraph 1.13, Diagram 1.4).¹ Approved Document K has no width relaxation because it sets no width for a private stair; for a spiral, the clear width that BS 5395-2 asks for still applies. Note that an alternating tread stair, which is only permitted in a loft conversion, still needs the full 2 m of headroom.¹

Wales, Scotland and Northern Ireland

Building standards differ, and Scotland is the one that does set widths. Clause 4.3 of the domestic Technical Handbook asks for an effective width of 900 mm for a private stair, 800 mm where a continuous handrail is fitted to both sides, or 600 mm where the stair serves only sanitary accommodation or one room, and it too sends spiral stairs to BS 5395-2:1984.⁶ Northern Ireland uses Technical Booklet H, Stairs, ramps, guarding and protection from impact.⁷ Always check with your local authority if the property is outside England: the 2013 edition of Approved Document K is published for use in England.¹

Material Options

Mild Steel (Powder-Coated)

The most common choice for kit staircases. Durable, readily available in standard and bespoke diameters, and available in any RAL colour. Steel kits balance cost and longevity well. Guarantees on the powder coating vary between manufacturers, so ask for the length in writing.

Stainless Steel

More expensive than mild steel but requires no painting and resists rust without ongoing maintenance. Particularly suited to contemporary homes or open-plan spaces.

Timber Treads on Steel Frame

A popular hybrid: steel central column and stringers with solid oak, ash, or pine treads. This combination adds warmth and is acoustically slightly better than all-steel. Cost sits between a basic steel kit and a full timber stair.

All-Timber

Bespoke timber spiral stairs (often oak or ash) are a premium product, typically crafted by specialist staircase joiners. They suit traditional or period homes but are expensive and require skilled installation.

Glass Balustrades

Glass panels (toughened or laminated) on a steel spiral significantly increase the perception of space and light. They add £800–£2,500 to kit costs depending on panel count and fixing method.

Spiral Staircase Cost

Kit Staircases (Supply Only)

Installed Costs (Supply + Fit, 2026)

Installation typically takes one to two days for a kit staircase. Labour rates for a specialist staircase fitter run £280–£400 per day in most of England, and usually more in London and the South East.

What to Factor into Your Budget

Floor opening (aperture): The upper floor needs a circular or square opening to suit the staircase. If this is structural (e.g., cutting through a joist), a structural engineer may be needed (£300–£800 for drawings) and the work will add £400–£1,200 to the build cost.

Building Regs fee: Councils set their own charges, so treat any figure as indicative and check your own authority’s scale before budgeting for a building notice covering a staircase installation.⁸ A registered building control approver is the alternative; compare its fee with the council’s.

Decoration and making good: Once the stair is in, the surrounding floor, ceiling, and walls will need finishing. Budget £200–£600 depending on how much disruption the installation causes.

Delivery: Spiral kits are bulky. Many suppliers include delivery; check before comparing quotes, as delivery can add £80–£200.

Choosing a Supplier and Installer

Several UK manufacturers supply spiral staircases direct to the public (with or without installation), including companies based in the West Midlands, Yorkshire, and the South East. Lead times for standard sizes are typically 2–6 weeks; bespoke or unusually large sizes can take 8–14 weeks.

Request a site survey before ordering, a reputable supplier will visit to check the floor opening, ceiling height, and overall fit, and will confirm Building Regs compliance in writing. If the supplier cannot provide compliance documentation, look elsewhere.

For kit installations, a competent joiner or metalworker familiar with staircases can fit most standard kits. For bespoke or glass-balustrade installations, use the manufacturer’s own fitters or a specialist they recommend.

A well-chosen spiral staircase is a practical, space-saving feature that can genuinely elevate an interior. Size it correctly for your use case, confirm Building Regs compliance upfront, and budget realistically for the floor opening and finishing work around it.