A 12 unit scheme crossing the major development line
An illustrative walkthrough of a 12 dwelling scheme, showing what changes once the ten unit major threshold and the affordable housing policy threshold are crossed.
Twelve dwellings is a major development, and almost everything about the submission changes at ten. That is the major development threshold example worth understanding before a site is bought, because the step from nine units to twelve adds a 13 week determination period, an affordable housing requirement in most authorities, the major form of the biodiversity net gain regime, a heavier consultation process and a planning obligation to negotiate.
The walkthrough below is an illustrative composite. The site, the figures and the sequence are illustrative, and no real authority or decision is described.
Why 12 units changes the submission
Major development for residential schemes means ten or more dwellings, or a site of 0.5 hectares or more where the number is not known. Crossing it has consequences that are procedural, policy-based and financial at the same time.
| What changes at 10 units | Consequence for a 12 unit scheme |
|---|---|
| Determination period | 13 weeks rather than eight |
| Affordable housing policy | Normally engaged, with a statement required |
| Biodiversity net gain | The major rather than small site form of the regime |
| Publicity | Press notice and site notice requirements for majors |
| Application fee | The major fee band, indexed annually |
| Planning obligation | A section 106 agreement in nearly all cases |
None of that makes a 12 unit scheme unviable, and it does mean the appraisal has to carry costs a nine unit scheme does not. Developers who buy on a nine unit assumption and then push to twelve during design are the ones who come unstuck.
Two things do not change. Environmental impact assessment screening is not engaged at this scale, because the Schedule 2 thresholds for urban development projects sit far above it. And the Statement of Community Involvement thresholds that apply to larger schemes are not reached, although some authorities expect engagement anyway.
Affordable housing policy and the statement
The affordable housing policy was engaged at eleven units, which meant a percentage requirement on the scheme as a whole rather than on the units above the threshold. That is the point most often misunderstood. The threshold is a gateway, not an exemption for the first ten.
With a policy requirement expressed as a percentage, twelve units produced a fractional number of affordable homes. Authorities deal with the fraction in one of three ways: round up to the nearest whole unit, round down and take a commuted sum for the balance, or take the whole requirement as a commuted payment where on-site provision is not practicable.
An Affordable Housing Statement sets out the tenure split, the unit mix, the location of the affordable homes within the scheme and the transfer arrangements. It also has to address tenure blindness and pepper-potting, because clustering the affordable units in one corner is the point officers raise most often.
Registered provider interest matters more at this scale than anywhere else. Twelve units generating two or three affordable homes is a small parcel, and providers are selective about taking them. Have that conversation before the tenure split is agreed, not after the obligation is drafted.
Community involvement at this scale
No statutory pre-application consultation applies, and the authority's own expectations may still be real. A letter to immediate neighbours and a single informal session is proportionate for twelve units, and it is worth doing because the objections you hear early are the ones you can design out.
A full Statement of Community Involvement is the document used on larger schemes, and for twelve units a two page note recording who was contacted, what was said and what changed in response is enough. The value is in the record rather than in the format.
Drainage, ecology and transport requirements
The evidence base grew in three places.
- Biodiversity net gain in its major form, with the statutory metric completed by a competent person, a 10 per cent gain secured for 30 years and a biodiversity gain plan approved before development begins
- A drainage strategy with the lead local flood authority as a statutory consultee on major development, which changes the review from an informal comment to a formal response
- A Transport Statement rather than a full Transport Assessment, since the scheme sits well below the thresholds at which an assessment is expected
That third point is where cost is saved. A Transport Statement covering trip generation, access, visibility, parking and refuse and servicing arrangements answers the question at twelve units. A full assessment with a modelled junction analysis is for schemes an order of magnitude larger, and offering one invites scrutiny the scheme does not need.
Ecology and arboriculture scaled with the site rather than with the unit count. The useful discipline is to ask, for each report, whether the authority's validation list requires it at this scale or whether it is being produced out of habit.
Section 106 and the viability discussion
The heads of terms covered affordable housing, an education contribution calculated from pupil yield, off-site open space, a travel plan monitoring sum and a monitoring fee. Nothing unusual, and the negotiation turned on two things.
The first was whether the education contribution was justified by capacity evidence for the specific schools, which is the question to ask whenever a per-pupil formula appears. The second was the cumulative weight of the package against the appraisal.
Where the package threatens viability, a Viability Assessment is the route, and national guidance expects the plan-making stage to have tested policy requirements so that site-specific assessment is the exception. On a twelve unit scheme the cost of producing and defending an assessment can approach the contribution being contested, so run that arithmetic before commissioning one.
Determination period and the extension of time
Thirteen weeks is the statutory period for a major application, and the realistic programme is longer. Consultee responses arrive at different times, the section 106 has to be concluded before the decision is issued, and the drafting is rarely on the critical path anyone planned.
Agree an extension of time in writing when it becomes clear the period will be exceeded. The alternative is an application that falls out of time, which gives a right of appeal against non-determination and achieves nothing useful on a scheme both sides expect to approve.
Start the obligation drafting at the point the officer indicates a positive recommendation, not at committee. Instruct your solicitor, get the title and any lender consent in hand, and give the authority a draft rather than waiting for theirs.
Lessons for the next site
- Model the scheme at both nine and twelve units during acquisition, with the major costs included in the twelve unit case
- Confirm how the authority handles the fractional affordable unit before fixing the mix
- Approach registered providers early, because small affordable parcels are hard to place
- Produce a Transport Statement, not an assessment, and say why in the covering letter
- Treat the biodiversity gain plan as a pre-development obligation with its own lead time
- Begin the section 106 drafting at the recommendation stage
A scheme that stays below ten units carries a lighter process, so the nine unit option deserves a proper appraisal rather than a glance. Where transport evidence has to go further than a statement, the dynamics are visible in a school expansion and the transport evidence. And where viability shifts the affordable offer during an application, the dynamics are covered in how viability changed the affordable offer on a mixed use scheme.
This is general guidance, not legal advice. For specialist technical reports, qualified professional input may be required. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.
Frequently asked questions
What counts as major development for housing?
Ten or more dwellings, or a site of 0.5 hectares or more where the number of dwellings is not known. Crossing that line brings a 13 week determination period, additional publicity requirements, the major fee band, the major form of the biodiversity net gain regime and, in most authorities, the affordable housing policy requirement.
Does the affordable housing requirement apply only to units above ten?
No. The threshold is a gateway rather than an exemption for the first ten units, so a percentage requirement applies to the scheme as a whole once it is engaged. At twelve units that usually produces a fractional number of affordable homes, which authorities handle by rounding, by a commuted sum for the balance, or by taking the whole requirement as a payment.
Do I need a Transport Assessment at 12 units?
Normally a Transport Statement is sufficient, covering trip generation, access, visibility, parking and servicing. A full assessment with modelled junction analysis is expected at much larger scales, commonly from around 50 units or 2,500 square metres. Offering an assessment at twelve units invites scrutiny the scheme does not need and costs more.
Is environmental impact assessment screening needed?
Not at this scale. The Schedule 2 thresholds for urban development projects under the 2017 Regulations sit well above a twelve unit scheme, whether measured by site area, dwelling numbers or floorspace. Screening becomes a live question on substantially larger sites or where the development falls within a sensitive area.
When should the section 106 drafting start?
At the point the case officer indicates a positive recommendation, not at committee. Instruct your solicitor, obtain the title and any lender consent, and offer the authority a draft rather than waiting for theirs. The obligation has to be concluded before the decision is issued, and it is the item most likely to push a major application beyond 13 weeks.
Sources and further reading
This article is general guidance about the planning system in England and, where stated, the rest of the UK. It is not legal or professional advice. Check your local planning authority’s validation requirements and take professional advice for your specific site.