Budgeting the evidence base for a nine unit scheme

Nine dwellings is a deliberate number. Ten is where major development starts, and with it a 13-week determination period, a wider consultation, affordable housing policy in most authorities, and a set of reports that a minor application can often avoid. Half a hectare does the same job where the unit count is not fixed.

That does not make the evidence base small. It makes it definable, which is the difference between a budget and an open cheque.

What stays out below the major development threshold

Four things usually fall away, though none of them is guaranteed.

Affordable housing. National policy generally sets the threshold at ten units or 1,000 square metres of floorspace, with a lower figure available in designated rural areas. Some authorities apply reduced thresholds where policy permits, so read the local plan rather than assuming.

Formal community involvement. Pre-application consultation with neighbours is good practice on any scheme, and a written record helps, but a full statement of community involvement is a major-scheme document.

A full Transport Assessment. The scale at which authorities expect one is much higher, usually fifty units or 2,500 square metres of floorspace. Below that a Transport Statement covering access, visibility, parking and refuse collection is normally proportionate.

Environmental impact assessment screening. Urban development projects fall to be screened at thresholds well above nine dwellings unless the site is in or near a sensitive area, in which case screening can still bite on a small scheme.

The documents almost every minor scheme needs

Start with the national requirements: the application form, the ownership certificate, a location plan, a site plan, existing and proposed drawings, the fee and the design and access statement where one is required.

Then the supporting documents that carry the argument:

• A Planning Statement setting the scheme against the development plan, naming the policies and answering each one. On a minor scheme this is the document that does the most work per pound spent.
• A Design and Access Statement where the site is in a conservation area or the council's checklist asks for one. Even where it is not required, a short design rationale usually helps.
• A topographical survey, which everything else is drawn on.
• A drainage strategy proportionate to the site.
• Ecology: a preliminary appraisal and the biodiversity net gain metric.
• Trees: a survey to BS 5837:2012 where there are trees on or next to the site.

That is the core. Everything beyond it should be traceable to a constraint you can point at on a map.

Biodiversity net gain on a small site

This is the one new fixed cost, and it catches people who last built out before April 2024.

Mandatory net gain applied to small sites from 2 April 2024. The uplift is ten per cent, secured for 30 years, with a biodiversity gain plan approved by the local planning authority before development begins. A simplified version of the statutory metric is available for small sites, which reduces the data entry rather than the ecological judgement behind it.

Two practical points. Run an indicative metric before the layout is fixed, because retaining a hedgerow or a single mature tree is close to free at sketch stage and impossible after the drainage design is set. And expect the habitat baseline survey to need the growing season, broadly April to September, which puts a date on when the work has to start.

The biodiversity net gain assessment should be completed by a competent person under the Environment Act 2021 regime, and a draft is a starting point for that professional rather than a replacement for them.

Drainage and highways evidence at this scale

On drainage, the lead local flood authority is a statutory consultee for major development, so on nine units the council may consult it informally or not at all. That is not a reason to skip the work. Councils refuse minor applications on surface water grounds, particularly where the scheme increases impermeable area on a site that already floods a neighbour's garden.

What a proportionate strategy contains at this scale: existing and proposed impermeable areas, infiltration testing results or a reason why infiltration is unsuitable, the proposed discharge point and its agreement in principle with the undertaker, attenuation volumes, and finished floor levels relative to any watercourse.

On highways, the local highway authority is consulted and its response is usually the one that determines the application. Give it what it needs: visibility splays drawn to the relevant standard, a swept path for a refuse vehicle, parking to the adopted standard, and cycle storage. A highways objection on a nine-unit scheme is almost always about one of those four.

Where a council asks for more than the national list

Local validation checklists are published by each authority and they vary considerably. Common additions on a minor housing site include a heritage statement where the site is near a listed building, a contaminated land desk study where the previous use warrants it, a noise assessment near a road or industrial use, an arboricultural impact assessment, an air quality assessment inside a management area, and a section 106 heads of terms.

Read the checklist before you commission anything. Then book pre-application advice and ask the officer, in writing, which items they consider necessary for this site. A written answer is worth more than the fee.

Illustrative example: nine houses on a former builder's yard next to a conservation area. The national list asks for the basics. The council's checklist adds a Phase 1 contamination desk study because of the previous use, a heritage statement because of the setting, and a tree survey for two mature limes on the boundary. That is three reports discovered from a web page rather than from a validation refusal six weeks in.

Sequencing spend against risk

The order matters more than the total.

1. Desk work first: constraint checks, the planning history, the local plan policies, the validation checklist. Low cost and decisive.
2. Topographical survey next, because every consultant works from it.
3. Pre-application advice, with a sketch layout and the specific questions you want answered.
4. Ecology appraisal and the indicative biodiversity metric, timed to catch the survey season.
5. Design development, informed by all of the above.
6. The remaining technical reports, commissioned against a fixed layout.
7. The planning statement last, so it describes the scheme you are actually submitting.

Reversing steps five and six is the classic expensive mistake. A drainage strategy written for a layout that then changes is a report bought twice.

Hold a contingency of a fifth of the technical budget for whatever the pre-application response turns up. On a site with any history at all, something always does: a sewer easement crossing the plot, an unrecorded well, a neighbour with a right of way. Finding it before submission costs a fortnight. Finding it after costs the determination period.

PlanScope drafts the planning documents in this list from your site information and flags where specialist input is legally required. You can see what a report costs before committing to the wider evidence base.

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