Open-riser staircases: what they are, and the rules that apply
Written by Scott Jones, The Stair Guys, independent staircase measuring and sourcing specialists·Last updated
An open-riser staircase leaves out the solid board that normally closes the front of each step, so there is a gap between one tread and the next. It is a clean, modern look, and it is perfectly allowed, but the gap is exactly the thing the rules care about, so open risers come with two conditions that are not optional.
The two rules that make it legal
First, the gap. The space between the treads must be small enough that a 100mm sphere cannot pass through it, the same 100mm rule that governs the gaps in the guarding, and for the same reason: so a small child cannot slip through. That limits how open the risers can actually be. See the guarding page.
Second, the overlap. Even without a riser, the treads have to overlap each other when seen from the side, so there is no straight gap for a foot to slide through the back of the step. In England that overlap is at least 16mm; in Scotland it is at least 15mm. This is covered on the building regulations page and in the stair dimensions. Both rules apply whatever the stair is made of.
Where they suit, and where to think twice
Open risers belong with the modern, open look: they are common on mono-stringer and cantilever stairs, and usually paired with a glass balustrade to keep everything light. The practical thing to weigh, rather than the look, is who uses the stair. Some people, and plenty of young children, find an open stair less reassuring to climb, and it needs the same care over grip as any stair. If that matters in your house, it is worth deciding before the stair is made, not after.
Frequently asked
Are open riser stairs legal in the UK?+
Yes, provided two conditions are met. The gaps between the treads must be small enough that a 100mm sphere cannot pass through, so a small child cannot slip through, and the treads must overlap each other, by at least 16mm in England or 15mm in Scotland. Meet both and an open-riser stair is compliant.
What is the gap rule for open riser stairs?+
The gap between the treads must be small enough that a 100mm sphere cannot pass through it, which is the same rule as the gaps in the guarding. It is there to stop a small child slipping through the open stair, and it limits how large the open gaps can be.
Do the treads on an open riser staircase need to overlap?+
Yes. Even without a riser board, the treads must overlap when viewed from the side, so there is no straight gap for a foot to slide through the back of the step. In England the overlap is at least 16mm; in Scotland it is at least 15mm.
Related guides
- Winder staircases: what they are and the rules that govern themA winder staircase turns a corner on tapered treads instead of a flat landing. Here is how winders work, the two rules every winder has to keep, why four winders is a harder job than three, and when a landing is the better answer.
- Types of staircase: the main shapes, and how to chooseThe main staircase types are straight, quarter-turn, half-turn, winder, spiral, helical and space-saver, with open or closed strings on each. The right one is driven by the space you have, the look you want and the budget.
- Space-saver (alternating tread) stairs: what they are and when you can have oneWhat a space-saver or alternating tread staircase is, when building regulations actually allow one, the trade-offs, and why it is a space and budget compromise rather than a premium upgrade.
- Mono-stringer and central-spine staircasesA mono-stringer or central-spine staircase carries the treads on a single central beam instead of two side strings, giving a lighter, floating look. The spine can be steel or a thick timber beam, and the treads cantilever out to each side.
- Cut string vs closed string staircase: the difference, and how to chooseA closed string staircase has a solid raking board on the outer edge that hides the ends of the treads, while a cut or open string has that edge cut to the step profile so the tread ends show. Closed is simpler and cheaper, cut is a feature with more joinery.
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