Changing from a spiral staircase to a conventional one

Replacing a spiral staircase with a conventional straight, quarter-turn or winder stair can make a home feel more open and give a more familiar route between floors. It is a good change to make. It is just not the like-for-like swap most people picture, because the two types of stair use the space in completely different ways.

Here is the bit that catches people out. If you expect the new flight to land where the spiral did, the logic does not hold, because the only reason the spiral sat in that footprint is that it was a spiral. It turns around a central column precisely so it can occupy a small square of floor. A conventional stair needs a longer, straighter run across the floor plan, and that is the whole reason you are replacing it. Put simply, if the new stair could sit exactly where the old one did, you would be fitting another spiral.

So the final position of the new stair is set by the stairwell opening, the floor to floor height, the available headroom, the structural supports and safe rise and going dimensions. It is not set by where the old spiral happened to sit, and expecting it to land in the same place is where most of the surprises come from.

What actually comes up on site

Existing walls are rarely straight or square. Older properties especially have walls, floor edges and landings that are out of plumb or out of square. A staircase can be made accurately to the agreed dimensions and still meet a wall that is not. Small gaps between the new stair, the wall and the landing should be expected, and they are closed with scribed trim, infill, caulk or decorating work rather than by remaking the stair.

Headroom can dictate the layout. Moving a flight or a top newel post to line up with an existing handrail also moves the lower part of the stair. That can push the bottom of the flight under a ceiling or a floor structure and lose the clearance. A position that looks neater is not always one that is safe or practical, and headroom is usually the constraint that decides the argument.

Landings and handrails often need altering. A spiral meets the upper floor differently from a conventional stair. New handrail sections, spindles, newel posts, landing edge adjustments or finishing work are commonly needed to end up with a safe, continuous balustrade rather than two systems meeting awkwardly.

The opening may limit the design. A stairwell sized for a spiral can restrict the width, the angle, the number of turns and the landing arrangement possible for a conventional replacement. The right answer balances appearance, comfort, structure and compliance, and sometimes the opening itself has to change.

Safety and compliance

Spiral and helical stairs are designed under different guidance from conventional stairs. In both England and Wales they are designed in accordance with BS 5395-2: England's Approved Document K says so at paragraph 1.28, and the Welsh Approved Document K at paragraph 1.21. So a spiral that was perfectly acceptable is not evidence that a conventional stair in the same opening will be, because it was never judged against the same figures.

For the conventional stair that replaces it, the ones that bite on a conversion are headroom of at least 2m over the whole route (England AD K paragraph 1.11 and Diagram 1.3, Wales paragraph 1.10), the rise and going limits for a private stair, clear width, and guarding. The guarding rules are set out on our staircase guarding and balustrade page, and the rise, going and pitch figures on the private stair dimensions page.

Requirements vary with the property, the design and local Building Control interpretation, so treat every conversion as its own assessment rather than assuming what was allowed next door.

What we would want to look at first

Before committing to a spiral to conventional conversion, get a proper site survey and a conversation about all of this:

• The available stairwell opening and the floor to floor height.
• Headroom along the full route of the new stair, not just at the top.
• The condition and alignment of the existing walls, landings and handrails.
• Which items are structural stairwork and which are decorating or finishing works, agreed before anyone starts.
• Any extra handrail, spindle, trim or landing alterations needed for a finished appearance.

That fourth point is worth settling in writing. A new staircase can be made accurately to the agreed dimensions, and the final look still depends on the existing building fabric and the finishing work carried out around it. Knowing in advance who is doing the trim, the making good and the decorating is the difference between a job that ends cleanly and one that ends in a conversation about gaps. On which note, the finishing itself is almost certainly yours: see whose job it is to finish a new staircase.