Staircase Building Regulations UK: Part K Dimensions Explained
UK staircase regs (Part K): rise 150-220mm, going at least 220mm, max pitch 42 degrees, 2m headroom. See the dimensions a compliant stair must hit and how to check your quote.
Stairs are one of the most tightly regulated parts of a home, because a stair built to the wrong dimensions is a genuine fall risk. Whether you are converting a loft, replacing a staircase, or extending, the numbers in Approved Document K are not suggestions. Here are the dimensions a compliant private staircase must hit and what to check on your quote.
The core dimensions
For a private (domestic) staircase: each rise between 150mm and 220mm; each going (the depth of each tread) at least 220mm; the rise and going the same all the way up a flight; a maximum pitch of 42 degrees; and 2 metres of headroom above the pitch line. As a sense check, twice the rise plus the going should land between 550mm and 700mm. Always confirm against the current Approved Document K, as figures are periodically updated.
In plain terms: stairs cannot be too steep, the steps cannot be too shallow front to back, and you cannot bang your head. The "twice rise plus going" rule is the quick test builders use to check a flight feels right underfoot.
Headroom, and the loft exception
The standard is 2 metres of clear headroom above the line of the stair. That is easy in a normal house and often impossible in a loft conversion, so the regulations allow a specific reduction.
For a loft conversion, where full 2 metre headroom cannot be achieved, the minimum is 1.9 metres measured at the centre of the stair width, reducing to 1.8 metres at the edge. Below 1.8 metres at the side, the stair does not comply. This single dimension is the most common reason a loft conversion staircase has to be repositioned, so it is worth checking early.
Our guide to loft conversion headroom and staircase rules covers the loft case in detail, and loft conversion costs covers the budget.
Handrails and guarding
- Handrail height: 900mm to 1000mm from the pitch line or floor.
- Both sides: stairs wider than 1 metre need a handrail on each side.
- Guarding: open sides and landings need guarding (a balustrade), and the gaps must be small enough that a 100mm sphere cannot pass through. This is the rule that bans wide-gap balustrades where children could slip through.
Width and flights
There is no fixed minimum width for a private stair in England, but 800mm to 900mm is normal and anything much narrower is awkward and may fail on usability. A long flight should have a landing to break it up, and a stair should not rise more than a set number of steps without one. Winders (tapered treads on a turn) have their own going rules measured at the centre of the tread.
Why this matters for your quote and your sale
A staircase that does not meet Part K is a building regulations failure. If it is part of a loft conversion or extension, Building Control will pick it up, and an uncompliant stair can hold up sign-off. Even outside a formal job, a non-compliant stair shows up on surveys and can complicate a sale.
If your quote includes a new or relocated staircase, check it commits to Part K: a pitch no steeper than 42 degrees, the rise and going within the limits, and the headroom (2 metres, or the 1.9/1.8 metre loft allowance). A quote that promises a staircase will fit a space that physically cannot meet the 42 degree rule is promising something that will not pass.
Check your quote
If you are holding a quote for a loft conversion, extension, or staircase replacement, upload it and we check whether the staircase and the other key building regs measurements are addressed, or whether the quote has glossed over a dimension that will not pass Building Control. It takes under a minute.
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