Accessible and adaptable dwellings: the required proportions

There is no national proportion of accessible homes. The M4(2) and M4(3) proportion requirement on your scheme comes from the adopted local plan, and if the plan has no policy, the authority cannot require either standard. That surprises developers who have assumed an accessible housing requirement applies everywhere, and it surprises them again in London, where Policy D7 of the London Plan sets 10 per cent of dwellings to the wheelchair user standard and the remaining 90 per cent to the accessible and adaptable standard. The variation between those two positions is the whole subject.

The optional requirements and how they work

Part M of the Building Regulations sets three levels for dwellings. M4(1) visitable dwellings is the mandatory baseline and applies everywhere. M4(2) accessible and adaptable dwellings and M4(3) wheelchair user dwellings are optional requirements, which means they apply to a development only where a planning condition imposes them.

M4(3) splits further. The wheelchair adaptable version requires the dwelling to be capable of simple adaptation for a wheelchair user, while the wheelchair accessible version requires it to be ready for occupation by a wheelchair user on completion. Which version applies is decided by the policy and the condition.

The mechanism matters. These are building regulations requirements triggered by a planning condition, so the planning permission creates the obligation and building control enforces the detail. A condition that simply says dwellings shall be accessible, without naming the standard and the proportion, is poor drafting and causes arguments at building control stage.

As at October 2026 the government has stated an intention to raise the mandatory baseline to the M4(2) standard, and that change has not been brought into force. Check the current position before relying on either state of affairs, because commencement would remove the need for a local policy to require M4(2) at all.

Why a local plan policy is needed

Planning guidance on optional technical standards is explicit that the optional requirements can only be applied through a local plan policy, and that the policy has to be justified.

The evidence an authority needs covers the need for accessible housing in its area, usually drawn from population projections, disability prevalence and housing register data, the effect on viability of imposing the standard, and site-specific factors such as topography and flood risk where a level approach is harder to achieve.

For M4(3) the guidance adds a further constraint: wheelchair user dwellings should only be required where the authority is responsible for allocating or nominating a person to live in that dwelling. In practice that ties the wheelchair accessible requirement to affordable tenures, with the adaptable version used for market housing where the policy covers it.

So two questions answer the proportion for your site. Does the adopted plan contain an optional standards policy, and does the authority's evidence base support the proportion it states. The second question matters at examination and occasionally at appeal, less so on a single application.

Proportions set in policy

Because the figure is local, the only safe approach is to read the policy. The pattern that recurs is a split between the two standards with the wheelchair element tied to affordable housing.

Check three things in the policy text beyond the headline figure. Whether the proportion applies to all dwellings or only to those above a scheme size threshold. Whether the M4(3) element is adaptable or accessible. And whether there is a viability or site-constraint exception, and what evidence it requires.

Rounding is worth settling early. On a scheme of 38 dwellings a 10 per cent wheelchair requirement is 3.8 units, and the authority's convention on rounding, usually upwards, changes your mix.

Wheelchair user dwellings and their design

The wheelchair standard is the one that drives layout, and the difference between adaptable and accessible is practical rather than theoretical.

The provisions that shape the design include a step-free approach from the parking space and from the street, a level threshold, wider doorsets and clear corridor widths, turning space in the principal rooms, a bathroom or wet room with the drainage and structural provision for adaptation, provision for a through-floor lift or a stair lift route in houses, and a parking space sized for transfer with a safe route to the entrance.

For adaptable dwellings, much of this is provision for future works: the drainage falls, the structural support for hoists and grab rails, and the space for a future lift, built in now rather than retrofitted. For accessible dwellings the works are done.

The consequences on a scheme are concentrated in a few places. Parking spaces for wheelchair users are wider and must be close to the entrance, which affects the parking layout. In flats the lift and core design is affected, as is the number of dwellings served per core. On sloping sites the step-free approach can determine the finished floor level and therefore the earthworks.

The evidence a council needs to adopt the standard

If you are responding to a draft local plan policy rather than applying an adopted one, the test is whether the evidence stacks up.

What the authority should be able to show: a quantified need for accessible and wheelchair housing in the area, the proportion derived from that need rather than borrowed from elsewhere, a viability assessment that includes the cost of the standard alongside the other policy requirements, and consideration of site typologies where the standard is difficult, such as steeply sloping or flood-prone sites.

Where the evidence is thin, the proportion is open to challenge at examination. Where it is sound, the proportion is a fixed input to your appraisal and should be treated as such from the first land bid.

Effect on layout and core design

Bring the requirement into the design at the concept stage, because retrofitting it into a fixed layout is where the cost appears.

Four points carry most of the consequence. Step-free approach dictates levels, so set the finished floor levels and the external level strategy with the accessible units identified. Parking position and dimension affect the layout, so locate accessible spaces before the street geometry is frozen. Core efficiency in flats changes with lift provision, so test the dwellings-per-core count early. And the distribution of accessible units matters: a policy or a condition may require them to be spread across tenures, storeys and dwelling sizes rather than clustered in the least valuable corner of the scheme.

The same logic applies across the other scale-triggered policy requirements, and mapping them together at the outset avoids discovering them one at a time. The energy and carbon requirements follow a similar pattern, as set out in energy and carbon requirements by scheme scale, and the health thresholds follow their own, covered in health impact assessment thresholds and content.

Checking the requirement before design freeze

A short checklist, done once, before the layout is committed.

1. Read the adopted plan policy on accessible and adaptable housing, and note the date of adoption.
2. Note the proportions, the standards named, the threshold at which they apply, and the rounding convention.
3. Identify whether the M4(3) element is adaptable or accessible, and which tenures it attaches to.
4. Check any supplementary planning document or design guide for the authority's expectations on distribution and on parking.
5. Confirm with the case officer at pre-application, in writing, how the proportion is calculated on your unit mix.
6. Record the answer in the Affordable Housing Statement and in the design and access material, with the accessible units identified on the layout drawing.

An Equalities Impact Assessment is a different document serving the public sector equality duty rather than the Building Regulations standard, and the two are sometimes confused in validation correspondence. Keep them separate and say which is which.

This is general guidance, not legal advice; check the position with your local planning authority or a qualified professional before relying on it. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.