Steel spiral staircases, made in Westerham

Where a spiral staircase earns its place

A straight stair climbing 2.7 metres takes three to four metres of floor. A spiral makes the same climb inside a circle 1.4 to 2 metres across, so spiral stairs suit lofts, mezzanines and basements, and the outside of a house where a balcony or roof terrace needs a way down to the garden.

They are the usual answer for a second stair: a fire escape from a flat above a shop, access to an office over a workshop, or a private route from a bedroom to the garden. We fit them in houses and commercial buildings across London, Kent and Surrey.

A spiral is poor at carrying furniture; a wardrobe or a sofa will not go up one. If it is the only stair to a bedroom, weigh that up first, or go for a larger diameter.

Diameter, rise and how it feels to climb

Diameter decides most of it. At 1,200mm you have a tight stair for occasional use to a single room; 1,400 to 1,600mm suits most houses; 1,800mm and above feels close to a normal staircase and is what an office, shop or shared building needs. The going is measured on a walking line part way out from the column, so a bigger circle gives a longer going and an easier climb.

BS 5395-2 sorts spiral and helical stairs into categories A to E, from a small private stair to a public one, and sets a minimum tread width and going for each. Approved Document K points to it for spirals and wants two metres of headroom all the way round.

A 2.7 metre floor to floor gives 13 or 14 risers of about 200mm, roughly one full turn.

Column, treads and balustrade

Everything stacks on a centre column, a circular hollow section around 114 or 140mm across, on a base plate bolted down. Each tread is a steel plate welded to a sleeve that slides over the column, or the whole flight is welded up in the workshop where access allows.

Outside, treads are chequer plate, open grating, or perforated plate where you want it to drain and look tidy. For indoors, a steel pan that takes a 30 to 40mm oak or stone infill is the usual choice, or a plain plate with a rubber or carpet insert.

The balustrade is normally vertical bars spaced so a 100mm ball cannot get through through, with a continuous handrail rolled to the helix in flat bar, tube or stainless: 900mm high inside a house, 1,100mm on an outside landing. Glass suits the larger diameters.

External spiral staircases and fire escapes

Outside, a spiral is hot-dip galvanised after welding, then powder coated if you want colour. Open grating or perforated treads let rain through. The column base sits on a concrete pad with resin anchors, and taller stairs get a wall tie at the landing to stop sway. Guarding is designed to the loads in BS 6180.

Approved Document B accepts a spiral as an escape stair if it is designed to BS 5395-2, and a stair the public will use has to be category E. If yours is the escape route from a flat, an office or a commercial unit, say so at the start and we check the category before we draw it. Where a spiral will not pass, a compact straight stair with a half landing usually will; we make external staircases and fire escapes both ways.

Internal spiral staircases and finishes

Inside, most spirals are powder coated, usually black or anthracite, though any RAL colour is available. The alternative is primer from the workshop and a painted finish on site, which is easier to touch up after the decorators. Stainless is left brushed.

Risers are open, which keeps the stair light and lets daylight through to the floor below. In a house the open gap must not let a 100mm sphere through, so tread depth and any riser bar are set to suit. Where the stair arrives at a mezzanine edge rather than through a hole in the floor, the top landing is a steel platform with matching guarding.

Getting it in is rarely a problem. A spiral arrives as a column and a stack of treads and is built in place, so a standard doorway is enough.

Survey, price and lead time

Send a photo of the space and the floor to floor height and you will have a written estimate within the working day. A free site survey follows. We measure the height, look at how the opening in the floor above will be formed and which joists it crosses, confirm headroom round the full turn, and check where the base will sit. We provide drawings and structural calculations for Building Control where needed.

Price follows diameter, height, tread type, balustrade and finish, with access and a new concrete base priced separately if needed. Once you approve the drawing the quotation is fixed unless the design changes.

A spiral is a few weeks in the workshop, then a week or so at the galvanisers or powder coaters. Fitting is usually a day. Phones are answered 24 hours a day.

Straight answers on spiral staircases