Staircase accessibility: Approved Document M and the M4 categories (England)
Written by Scott Jones, The Stair Guys, independent staircase measuring and sourcing specialists·Last updated
Alongside the safety rules in Approved Document K, England has accessibility rules for dwellings in Approved Document M, Volume 1. Since 2015 these are split into three categories, and the higher two are optional, which surprises people. Understanding which category applies to your home decides whether the staircase has anything extra to meet.
The three categories
- M4(1), visitable dwelling. The baseline that applies to all new homes. For internal stairs it simply defers to Approved Document K, so there is no extra stair-width rule beyond the normal Part K figures.
- M4(2), accessible and adaptable dwelling. An optional, higher standard. Its internal stair must have a clear width of at least 850mm, measured 450mm above the pitch line and ignoring the newel post, so that a stairlift could be fitted later. The side without a handrail has to allow a second handrail to be added in future while keeping that 850mm clear.
- M4(3), wheelchair user dwelling. The highest, also optional. The internal stair again needs the 850mm clear width, and space must be provided for a through-floor lift (installed at completion for a wheelchair accessible home, or the structural space reserved for one in a wheelchair adaptable home).
Optional, and England-only
The important thing about M4(2) and M4(3) is that they are optional requirements. They do not apply automatically. They only bite where a planning condition, set when planning permission is granted, requires a dwelling to meet that category. Where no such condition is imposed, a new home only has to meet M4(1), which for stairs means the ordinary Part K figures.
This M4 system is specific to England. As covered in our Wales guide, Wales never adopted M4(2)/M4(3); Scotland and Northern Ireland use their own accessibility provisions instead (for example Scotland's stairlift-parking rule). So the 850mm stair-width requirement is not a UK-wide rule, it is an English optional one. For the core stair figures that apply everywhere in England, see the UK staircase building regulations guide.
Frequently asked
What is the minimum stair width for a stairlift under Approved Document M?+
850mm clear width, measured 450mm above the pitch line and ignoring the newel post, for the internal stair in an M4(2) or M4(3) dwelling. It is there to allow a stairlift to be fitted in future. This is an England requirement, and it applies only where a planning condition requires M4(2) or M4(3).
Are M4(2) and M4(3) mandatory for new homes?+
No. They are optional requirements that apply only where a planning condition, imposed when planning permission is granted, requires a dwelling to meet that category. Otherwise a new home only has to meet M4(1), which for internal stairs simply follows Approved Document K.
Does the 850mm accessible stair width apply across the UK?+
No. The M4(2)/M4(3) system and its 850mm stair width are specific to England. Wales did not adopt M4(2)/M4(3), and Scotland and Northern Ireland have their own accessibility provisions, so the 850mm figure should not be assumed outside England.
Sources
Primary sources we used and reconciled before publishing.
Related guides
- UK Staircase Building Regulations, ExplainedThe building regulations for stairs in England, Wales, Scotland and Northern Ireland, in plain English. Rise, going, pitch, headroom, guarding and handrails, every figure sourced.
- Staircase headroom: how much you need and how to check itHow much headroom a staircase needs under UK building regulations: the 2 metre rule, the reduced loft-conversion allowance, where headroom is tightest, and how to check it properly.
- Staircase handrail requirements: height, sides and gripWhat UK building regulations require of a staircase handrail: the 900mm to 1000mm height, when you need one side or both, and why a wall-mounted rail needs proper clearance and grip.
- Staircase guarding and balustrade: height and the 100mm ruleWhat UK building regulations require of staircase guarding and balustrade: where it is needed, the 900mm height, the 100mm sphere gap rule, and why it must not be easy for a child to climb.
- Private staircase dimensions: rise, going and pitchThe rise, going and pitch rules for a private (domestic) staircase in the UK, the 2R+G formula, why every rise must be equal, and the simple going = rise divided by 0.9 rule of thumb that keeps a stair within 42 degrees.
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