Approved Document M (Accessibility): What Homeowners Need to Know

Part M is divided into three volumes:

• M4(1) — Visitable dwellings: the minimum standard for all new dwellings. Covers step-free access to the entrance, minimum door widths and a WC on the entrance level.
• M4(2) — Accessible and adaptable dwellings: a higher standard, often required by local planning authorities. Includes wider corridors, level-access shower provision and future-proofing for adaptations.
• M4(3) — Wheelchair user dwellings: designed for wheelchair users from the outset.

For most homeowners doing extensions, M4(1) is the baseline; your local planning authority may require M4(2) for new dwellings through a planning condition.

When you build an extension that adds a new entrance or significantly alters the approach to the dwelling, M4(1) may require:

• Level or ramped access to the principal entrance: maximum ramp gradient 1:15 (or 1:12 for short ramps), with a level landing at top and bottom.
• Minimum doorway clear opening width: 775 mm for the principal entrance (775 mm is the clear opening width with the door open to 90°; this requires a 900 mm door leaf).
• Level threshold: the entrance threshold should have no upstand greater than 15 mm.
• WC at entrance level: new dwellings must have a WC accessible from the entrance level without needing to use stairs.

M4(2) goes further than M4(1) and is increasingly required by local planning authorities for new dwellings. It requires:

• Wider corridors: 900 mm clear for straight runs, 1,200 mm at 90° turns
• A level-access shower (or space to install one) on the entrance level
• Bedroom and living room on the entrance level (or space provision for a through-floor lift)
• Stronger walls in bathrooms for future grab rail installation
• Lower window cill heights for views from a seated position

Check whether your planning permission includes a condition requiring M4(2) or M4(3) before you finalise your building regs submission.

The most common Part M challenge for extensions is achieving level or ramped access at the entrance, particularly where there are changes in level between the garden and the ground floor. Practical solutions include:

• Cutting the ground level in front of the extension entrance to create a level threshold
• A permanent ramp with maximum gradient 1:15 and handrails on both sides
• A platform lift (requires planning permission in some areas)

Where level access is genuinely not achievable due to existing site conditions, building control may accept a reasonable provision given the constraints.

For new dwellings, building control will check M4(1) compliance at the Full Plans stage and again at the final inspection. M4(2) and M4(3) compliance is often checked through a detailed schedule of accommodation submitted with the Full Plans.

For extensions, building control will assess whether the extension triggers M4 requirements and what proportion of the work is new (as opposed to alterations to existing). In many cases, a single-storey rear extension will only need to comply with M4 at the new external door.