Counting units correctly for the major development test

Ten dwellings is the number that changes everything on a small residential scheme, and how to count dwellings for major development is not as obvious as it looks. The definition sits in article 2 of the Town and Country Planning (Development Management Procedure) (England) Order 2015, and it is written around dwellings to be provided rather than the net increase in homes on the site. Demolish one house and build ten, and you may well have a major application even though the site gains only nine.

Getting the count wrong costs time. A scheme submitted as a minor application and then reclassified loses its validation date, picks up a different determination period and a newspaper advertisement, and may need documents nobody budgeted for.

Where the definition sits and what it says

Article 2 of the 2015 Order defines major development for procedural purposes. For residential schemes the two limbs that matter are the number of dwellinghouses to be provided, which is 10 or more, and the site area, which is 0.5 hectares or more where the number of dwellings is not known.

Two further limbs catch mixed and commercial schemes: the provision of a building or buildings where the floorspace to be created is 1,000 m² or more, and development carried out on a site of 1 hectare or more. Minerals and waste development are major regardless of scale.

Note that any one limb is enough. A scheme of six houses on 1.2 hectares is major on site area alone.

Provided, not net

The wording is dwellings to be provided. That is a gross count of what the development creates, which is why replacement and redevelopment schemes catch people out.

An easy way to test yourself: if the application were granted and built, how many dwellings would the development have provided? Not how many more would exist than before.

Authorities do not always apply it the same way, and some treat the count as net for certain purposes such as affordable housing policy, where the local plan wording governs instead. The pragmatic step is to ask the validation team in writing before you submit, quote the article 2 limb you think applies, and keep the reply on file. That one email prevents the argument later.

Replacement dwellings and demolition

Take a bungalow on a large plot, demolished and replaced by ten houses. Ten dwellings are provided. The site is also likely to exceed 0.5 hectares, so both limbs may be engaged.

Conversions behave differently. Subdividing an existing house into flats provides new dwellings, and those new dwellings count. A conversion of a single house into four flats provides four dwellings, not three, even though the net gain is three.

Where the site includes existing dwellings that are retained and untouched, they are not provided by the development and do not count. Retained dwellings still matter for other purposes, including the red line boundary, ownership certificates and the site area limb.

Flats, student accommodation and houses in multiple occupation

A block of flats provides as many dwellings as there are self-contained flats, which is straightforward.

Houses in multiple occupation are not. An HMO in use class C4 is generally treated as a single unit, because the building is one dwelling in planning terms even though several households live in it. Purpose-built student accommodation and co-living schemes are usually sui generis and are not dwellings at all, so authorities commonly fall back on the floorspace limb or the site area limb to classify them.

Practice here varies more than anywhere else in the definition. If your scheme involves anything other than ordinary C3 houses and flats, agree the classification with the case officer at pre-application stage.

Phasing, and the problem with slicing a site

The definition applies to the development described in the application. Splitting a site into two applications of six dwellings each will, on the face of it, keep both below the threshold.

It rarely works. Where the two parcels are in the same ownership, share an access, and are plainly part of one scheme, an authority can treat them as a single development and require the major procedure. Environmental impact screening also looks at cumulative effects, so an artificially divided site is still assessed as a whole for that purpose. And the practice is visible: consecutive application references on adjoining red lines invite scrutiny.

There are honest reasons to phase a site, including land assembly, infrastructure sequencing and cash flow. The safe approach is to explain the phasing openly in the covering statement and to show how the wider site works, rather than to hope nobody notices. The trade-offs are set out in more detail in the discussion of splitting a site below a planning threshold.

Mixed use schemes and the floorspace limb

On a scheme with flats above commercial floorspace, count both limbs separately. Nine flats over 1,100 m² of retail is major on floorspace even though the residential limb is not met.

Floorspace to be created is normally read as gross floorspace of the new building or buildings, not the net change in floorspace. Demolishing a 900 m² shed and building a 1,100 m² unit creates 1,100 m².

Where a scheme is close to a limb, measure the floorspace properly from the drawings and put the figure in the application form and the covering material. A case officer who has to work it out themselves will round up.

What actually changes once a scheme is major

Classification is procedural, and the consequences are practical:

1. The determination period becomes 13 weeks rather than eight, and 16 weeks where the development is subject to environmental impact assessment.
2. Publicity increases. A newspaper advertisement is required as well as a site notice or neighbour notification.
3. An Affordable Housing Statement is normally expected at 10 or more dwellings, and the local plan's affordable housing policy engages.
4. Biodiversity net gain transitional arrangements differ between major and small sites, so check which regime applies to the application.
5. The scheme is more likely to go to committee rather than being decided under delegated powers.
6. The application fee is calculated on a different band, and fees are indexed annually, so use the current published schedule rather than an old figure.

Design expectations rise too. A major scheme is usually expected to arrive with a fuller evidence base, and the list of supporting reports a residential scheme needs grows with the unit count rather than in proportion to it.

Writing the description of development

The description on the application form is what the classification is applied to, so write it precisely. State the number of dwellings, whether any existing buildings are being demolished, the site area, and any non-residential floorspace.

A description such as "residential development" with no numbers invites a validation query and gives the authority room to classify the scheme however it wishes. "Demolition of one dwelling and erection of 10 dwellings with associated access, parking and landscaping" leaves nothing to interpret.

And keep the description consistent with the drawings and the schedule of accommodation. Where the three disagree, the validation team will use the least helpful reading. That is not unfair, it is simply what happens when an officer has to pick one.

Count the units, measure the floorspace, measure the red line area, then decide which route you are on before you commission anything.

This is general guidance, not legal advice. Thresholds and procedural requirements change, so 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.