Why nine units and ten units are different applications

Ten dwellings is a major application and nine is a minor one. That single unit changes the determination period from eight weeks to 13, brings affordable housing policy into play on most sites, triggers a wider consultation and publicity regime, and adds several documents to the validation list. For a small developer with a site that could hold either, the question is whether the tenth unit pays for what it drags in.

Often it does not. Sometimes it clearly does, and the way to tell is to price the difference rather than guess at it.

What the major threshold changes procedurally

Major development for residential purposes means 10 or more dwellings, or a site area of 0.5 ha or more where the number of dwellings is not known. The definition sits in article 2 of the Town and Country Planning (Development Management Procedure) (England) Order 2015, and a string of procedural consequences hang off it.

Note the site area limb of the definition. A nine unit scheme on 0.6 ha is still a major application by area, so trimming the unit count does not help if the red line is large. Developers who discover this late have usually already drawn the scheme.

Affordable housing contributions at ten units

National policy sets a threshold below which affordable housing contributions should not be sought on most sites, expressed by reference to major development, with a lower threshold in designated rural areas where authorities may apply five units or fewer. Check the adopted local plan, because the local policy and any rural threshold are what actually bind.

The effect at ten units is a step rather than a slope. A scheme of ten with a 30 or 40 per cent policy requirement delivers three or four affordable homes, or a commuted sum of comparable value, and that comes off the land value directly. An Affordable Housing Statement is then needed to set out the tenure split, the unit mix, the distribution across the site and the delivery mechanism.

If the scheme cannot carry the contribution, the route is a viability case, which brings its own cost and its own review mechanism. That is a reasonable argument on a constrained brownfield plot with abnormal costs. It is a poor argument on a clean greenfield site, and officers see the difference.

Determination period, publicity and consultee involvement

Thirteen weeks rather than eight sounds like five weeks of delay. In practice the gap is wider, because major applications attract more consultees and a committee date that may not align with the expiry.

The consultee list grows at the threshold. The lead local flood authority becomes a statutory consultee on major development for surface water drainage, which means a drainage design reviewed in detail rather than a drainage statement taken on trust. The local highway authority looks harder at access and trip generation. Where a scheme reaches the relevant size, Active Travel England comes in. The sewerage undertaker's capacity response matters more because ten connections are harder to absorb than nine. On sites near designated habitats, nutrient or recreational mitigation requirements can apply at either scale, and nutrient neutrality and the effect of scheme size sets out where the size question bites.

Many authorities also expect community engagement before submission on majors, documented in a Statement of Community Involvement. It is not a statutory requirement for an application of this size, and a committee that hears there was no pre-application engagement will say so.

A section 106 agreement becomes much more likely at ten units, covering affordable housing, open space or play contributions, education where the authority's formula bites, and monitoring fees. Solicitors on both sides, four to eight weeks of drafting, and an extension of time to accommodate it.

Evidence base cost at the step change

The documents that appear or get heavier at ten units are predictable.

• Biodiversity net gain through the full statutory metric rather than the small sites route, with an ecologist appointed for baseline survey and metric completion by a competent person under the Environment Act 2021.
• A drainage design to the national SuDS standards, with infiltration testing, attenuation sizing and a maintenance plan, because the lead local flood authority will read it.
• Transport evidence: a transport statement at this scale rather than a full Transport Assessment, which arrives at higher thresholds, plus a travel plan in some authorities.
• An affordable housing statement and, if contested, a viability appraisal.
• Energy and sustainability material, with requirements that differ by authority and by scale, covered in energy and carbon requirements by scheme scale.
• A statement of community involvement and the engagement that sits behind it.

None of those is enormous on its own. Together they are the difference between a pack one person can assemble and a pack that needs a coordinating consultant, and the professional fees scale accordingly.

Designing to nine units deliberately

There is nothing improper about designing a scheme that sits below a threshold, provided the scheme is real and the application is honest about what it is. Nine larger houses on a site that could hold ten smaller ones is a legitimate design choice.

What is not legitimate is salami slicing: submitting two applications of five and five on the same land, in the same ownership, with the same access, to avoid the major threshold. Authorities aggregate where the proposals are functionally part of one scheme, and an inspector will look at the substance. Phasing a large scheme without gaming thresholds covers where the line sits.

Three tests before committing to nine. Does the red line stay below 0.5 ha, or does the area limb catch you anyway. Does the adopted local plan apply a lower affordable housing threshold, which in designated rural areas it may. And does the site allocation or the plan's density expectation point to a higher number, because a deliberately low density scheme on an allocated site can be refused for under-using land.

Where the tenth unit earns its place

The maths is straightforward once the costs are on the page. Set the gross development value of the additional unit against the policy contribution it triggers, the extra professional fees, the section 106 costs including monitoring, and the value of five or more weeks of additional programme.

On a site where units sell at a modest value and the affordable requirement is 40 per cent, the tenth unit frequently loses money. On a site in a higher value area, or where the site area limb has already made the scheme major, the threshold has already been crossed and the only question is how many units the site can take properly. That second case is the one worth checking first.

A worked illustration, with figures chosen to show the method rather than drawn from a real appraisal: add one unit at a value of V, deduct a policy contribution equivalent to roughly a third of total units as affordable, deduct the step in evidence base cost, and deduct carrying costs over the extra programme. Where V is small relative to the contribution and the fees, the answer comes out negative, and that is the common case on small sites in lower value areas. Run it with your own numbers before the layout is fixed.

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. Enter your postcode on PlanScope to see which reports your site is likely to need.