Staircase Building Regulations UK: Part K Dimensions Explained
In England a private stair needs a rise of 150mm to 220mm, a going of 220mm to 300mm, a maximum pitch of 42 degrees and 2m headroom. Wales and Scotland differ.
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) between 220mm and 300mm; 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.
These figures come from Approved Document K, 2013 edition, which applies in England only: Table 1.1 and its note 1 for the rise, going and pitch, paragraph 1.11 for headroom. Wales did not adopt the 2013 revision and works to its own, earlier edition of Approved Document K, whose rise and going ranges differ from the England figures above, so check the Welsh document rather than assuming these numbers carry across. Scotland works to the Building Standards Technical Handbook instead, where Table 4.3 gives a private stair a maximum rise of 220mm, a minimum going of 225mm and the same 42 degree maximum pitch, with a handrail at 840mm to 1.0m (clause 4.3.15), a minimum effective width of 900mm and 2.0m of headroom. Northern Ireland has its own Technical Booklet H. Always confirm against the document for your nation, 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.
Measure your own stairs in six steps
You need a tape measure and a spirit level or a straight piece of timber. This works on an existing staircase and on a drawn one, and it takes about ten minutes. All the England figures come from the table above.
- Count the risers, not the treads. A riser is a vertical face. A flight from one floor to the next always has one more riser than it has treads, because the top tread is the landing. Write the number down.
- Measure the total rise. Measure vertically from the finished floor at the bottom to the finished floor at the top. Do it against a wall with the tape held plumb, not up the slope of the stairs.
- Work out one rise. Divide the total rise by the number of risers. Every rise in a flight should be the same, so this single figure is the one to test. It must land between 150mm and 220mm. If your tape says the individual steps vary, that is a failure on its own: the rise and the going must be the same all the way up.
- Measure the going. The going is the horizontal depth of one tread from the face of one riser to the face of the next, not including the nosing overhang. Measure two or three treads, part way up the flight rather than at the ends. It must land between 220mm and 300mm.
- Check the pitch and the comfort rule together. You cannot measure 42 degrees with a tape, but you can divide. Divide your rise by your going: 42 degrees is a ratio of about 0.90, so anything above that is too steep. Then add twice the rise to the going. That total should land between 550mm and 700mm. A 200mm rise with a 220mm going gives a ratio of 0.91 and a total of 620mm, so it passes the comfort rule and fails the pitch. Both have to pass.
- Check the headroom where it is tightest. Hold a straight edge on the nosings to give you the pitch line, then measure vertically from it to the underside of whatever is above: the ceiling, a beam, the trimmer around the stairwell. You need 2 metres, or, in a loft conversion only, 1.9 metres at the centre of the stair width reducing to 1.8 metres at the edge. Measure at the worst point, not the average one.
Two more to check while you are there. The handrail should sit 900mm to 1000mm above the pitch line or floor, and a stair 1000mm or wider needs one on both sides. Any open side or landing with a drop of more than 600mm needs guarding with gaps too small for a 100mm sphere to pass through.
If a figure falls outside the range, that is a question for whoever is building or selling the stair, not a decision for you to make. Write down which of the six numbers failed and by how much, and ask them how they intend to meet Part K. These are the England figures: if you are in Wales, Scotland or Northern Ireland, run the same six steps against the document for your nation, because the ranges differ.
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 1000mm or wider need a handrail on each side (Approved Document K, paragraph 1.34c).
- 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. Approved Document K requires a landing at the top and bottom of every flight, and where a stair has more than 36 risers in consecutive flights it needs at least one change of direction between flights. There is no maximum number of risers per flight for a private stair in England, although Scotland's Technical Handbook limits a flight to 16 rises. 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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