The nine to ten unit cliff edge in a housing scheme

Ten dwellings is where a housing scheme stops being minor development and becomes major development, and almost everything about the application changes at that line. The Town and Country Planning (Development Management Procedure) (England) Order 2015 defines major development as development involving ten or more dwellings, or a site of 0.5 hectares or more where the number is not yet known. Nine units is a minor application. Ten is a major one, with a longer determination period, wider publicity, more consultees and, in most areas, an affordable housing requirement.

So the tenth plot has to earn its place. On a small site the extra unit frequently costs more in process, evidence and planning obligations than it returns in value, and the arithmetic is worth doing before the layout is fixed.

What major status changes in procedure

The determination period moves from eight weeks to 13. That is before any extension of time agreement, and on a site with ecology or drainage issues the real elapsed time is longer still.

Publicity changes as well. Under Article 15 of the Development Management Procedure Order, major development requires a notice published in a local newspaper in addition to a site notice or neighbour notification. More publicity means more representations, and more representations make a committee referral more likely.

The lead local flood authority becomes a statutory consultee on surface water drainage for major development. That alone usually means a drainage strategy with calculations rather than a paragraph in the design statement, and it has a habit of arriving late because the consultee response comes after validation.

Validation lists also split by scale. Most authorities apply a longer list of required documents to majors, and the difference between the nine unit list and the ten unit list is worth reading before you choose.

Affordable housing policy at the threshold

National policy sets the affordable housing threshold at major development, so schemes below ten dwellings are generally outside it. In designated rural areas authorities may apply a lower threshold, which matters a great deal in National Landscapes and the areas designated under section 157 of the Housing Act 1985.

Where the adopted local plan sets a percentage, ten units triggers it. The obligation is secured through a section 106 agreement, which adds legal costs, a monitoring fee and several weeks to the decision. Tenure and the split between social rent, affordable rent and intermediate products follow the local plan, and the detail of how that is agreed is set out in affordable housing tenure split on major sites.

Policy also deals with avoidance. Authorities look at whether an application forms part of a larger scheme, and at cumulative development on a site over time, so phasing nine units now and nine later is not a reliable route around the threshold.

An Affordable Housing Statement is the document that sets out the offer, the tenure mix and the policy compliance position. Where the scheme cannot meet policy, that statement has to be backed by a viability appraisal, which is a separate and expensive exercise.

Biodiversity gain under the majors regime

Mandatory biodiversity net gain applies to both nine and ten unit schemes. It came into force for major development on 12 February 2024 and for small sites on 2 April 2024, and the ten per cent requirement and the 30 year management obligation are the same either side of the line.

What changes is the metric. Small development, defined by reference to residential schemes of fewer than ten dwellings on a site under one hectare, can use the small sites metric, which is a simplified version requiring less survey input. At ten units the full statutory biodiversity metric applies, with habitat condition assessment across the site by a competent person.

That is a real cost step rather than a procedural one. The full metric needs a UK Habitat Classification survey with condition scoring, which has its own seasonal constraint, because most habitats cannot be assessed reliably outside the growing season.

The biodiversity gain plan must be approved by the authority before development begins in either case, and the metric calculation should be completed by a competent person under the Environment Act 2021 regime. An AI-assisted draft is a starting point for that professional rather than a replacement for the survey.

Statutory consultees and scrutiny at ten units

Beyond the lead local flood authority, the consultee list grows with the specifics rather than the number alone. National Highways is consulted where the strategic road network is affected at any scale. The Environment Agency is consulted on flood zones and on land contamination. Natural England appears where a designated site or a nutrient catchment is engaged.

A Transport Assessment is not usually triggered at ten units, since the thresholds for a full assessment sit much higher. A transport statement is the normal expectation at this scale, with a trip generation comparison and a note on access geometry.

Committee exposure is the less predictable change. Many authorities' schemes of delegation refer major applications to planning committee, or refer them where a set number of objections is received. Read the scheme of delegation for the authority rather than assuming, because the arrangements vary and they determine whether your decision date is governed by a committee cycle.

Evidence base cost either side of the line

The honest comparison looks like this.

The entries in the right hand column each carry professional fees, and the section 106 brings the authority's legal costs with it. On a site where land value per plot is modest, the tenth unit can be net negative once those are counted.

There is a counter-argument. A ten unit scheme that is going to be refused at nine for layout or density reasons may be better off as a major application with a proper evidence base behind it, and the policy support for making efficient use of land is stronger at that scale.

Deciding whether the tenth unit pays for itself

Work it as a simple comparison rather than a feeling. Take the net development value of the tenth plot. Subtract the affordable housing obligation attributable to the scheme, the section 106 legal and monitoring costs, the additional survey and report costs, and the holding cost of five extra weeks of determination plus any committee delay.

If the answer is close, look at what else changes. Does the site cross 0.5 hectares anyway, which makes it major regardless of unit numbers? Is the site in a designated rural area with a lower affordable threshold, which removes the benefit of staying at nine? Does the authority have a five year housing land supply position that affects how a borderline scheme is weighed?

Where the decision is finely balanced, the sensible move is a pre-application enquiry setting out both options and asking the authority which it would prefer to determine. The answer is free and it is usually candid. For the step below this one, where a single dwelling sits against householder work, the householder or minor line covers the same arithmetic at a smaller scale.

This is general guidance, not legal advice. Check the position with your local planning authority or a qualified professional before relying on it.

Enter your postcode on PlanScope to see which reports a scheme at either side of the ten unit line is likely to need.

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