Budgeting the evidence base for a major residential scheme
Crossing ten units changes the document list, the consultees and the budget. Sequencing the desk work before the intrusive work is what keeps the technical spend under control.
Crossing the major threshold at ten dwellings changes the evidence base more than it changes the architecture. A scheme of nine units and a scheme of eleven sit in different worlds for determination period, consultees, affordable housing and biodiversity, and the technical budget moves with them. On a greenfield major in England, the evidence base commonly runs to tens of thousands of pounds before a single drawing is issued for planning, and developer budgets of £50,000 and above for the technical pack on a major scheme are normal rather than unlucky.
The way to control it is sequencing. Commission the low cost work that tells you whether the expensive work is needed, and never commission a seasonal survey a month after its window closes.
What the major threshold brings with it
Major development for procedural purposes means ten or more dwellings, or a site of 0.5 hectares or more where the number is not known, or 1,000m² or more of floorspace for other development. Crossing it brings a 13 week determination period, a wider consultation and a longer document list.
The items that appear at or near ten units are the ones to budget first. An Affordable Housing Statement is expected where the affordable housing policy bites. Biodiversity net gain under the Environment Act 2021 has applied to major development since 12 February 2024 and to small sites since 2 April 2024, so the Biodiversity Net Gain Assessment and the baseline habitat survey behind it are not optional. A Design and Access Statement is required for major development under the Development Management Procedure Order 2015.
Then come the thresholds that depend on what the site is rather than how big it is. A flood risk assessment where the site is in Flood Zone 2 or 3 or is one hectare or more. A transport assessment where trip generation warrants it, with 50 units or 2,500m² a common trigger. A statement of community involvement on larger schemes. Lead local flood authority consultation on surface water drainage for majors.
Transport, drainage and ecology as the three big items
These three account for most of the spend on a typical major, and each has a hidden multiplier.
Transport costs escalate when the access strategy is not fixed. A Transport Assessment priced on a simple priority junction becomes a different commission when the highway authority asks for junction modelling, a speed survey, a road safety audit of the access design and a review of a second junction further along the corridor. Fix the access with the highway authority at pre-application stage and the fee stops moving.
Drainage costs escalate on infiltration. A strategy based on soakaways needs infiltration testing to the right standard, and if the tests fail you are into attenuation, flow control, a discharge agreement with the sewerage undertaker or a watercourse connection with a riparian consent. Budget for the possibility of the test failing.
Ecology costs escalate on seasons. A preliminary ecological appraisal can be done at almost any time of year, but it may recommend bat emergence surveys between May and September, great crested newt eDNA sampling between 15 April and 30 June, or reptile surveys across April to October. A survey window missed in March means a scheme delayed until the following year, and that delay costs more than the survey.
| Item | What drives the fee up |
|---|---|
| Transport assessment | Unfixed access, junction modelling, second junction, safety audit |
| Drainage strategy | Failed infiltration tests, offsite connection, undertaker agreement |
| Ecology | Seasonal surveys, protected species licensing, habitat creation design |
| Heritage and archaeology | Trial trenching after a desk based assessment |
| Contamination | Phase 2 intrusive investigation following a Phase 1 desk study |
Where EIA screening changes the budget
Screening is the single biggest branch point. An urban development project becomes screenable Schedule 2 development above the thresholds in the Environmental Impact Assessment Regulations 2017, and sensitive area status can bring a smaller scheme into scope.
Request a screening opinion from the authority rather than guessing. It costs the officer time and your agent's fee, and a negative screening opinion is worth having in writing before the technical commissions go out. If the opinion is positive, the Environmental Impact Assessment route changes the determination period to 16 weeks, requires an Environmental Statement prepared by competent experts under those Regulations, and multiplies the technical budget. A PlanScope draft is a starting point for that competent expert rather than a substitute for them.
Scoping follows. A scoping opinion narrows the chapters, and every chapter you remove at scoping is a chapter you do not pay to write.
Phasing the spend against risk
Spend in three tranches, and let each tranche decide the next.
- Desk work first. Constraints checks, a Phase 1 contamination desk study, an archaeological desk based assessment, a preliminary ecological appraisal, a flood risk screen against the published maps and a transport scoping note. This tranche costs the least and it tells you what the site actually is.
- Pre-application and screening next. A pre-application meeting, a screening opinion where relevant, an access meeting with the highway authority and an early conversation with the lead local flood authority. Nothing intrusive is commissioned yet.
- Then the intrusive and seasonal work. Ground investigation, infiltration testing, bat and newt surveys in their windows, trial trenching if archaeology is flagged, junction surveys and modelling.
The failure mode is commissioning tranche three in parallel with tranche one to save time. On a site where the desk study shows no contamination risk and the ecological appraisal finds no roost features, half of that spend was unnecessary.
Costs triggered by consultee responses
Budget a contingency specifically for consultee driven work, because it is the line that overruns. Expect the Environment Agency to ask for modelling where the site is near a main river, the lead local flood authority to query discharge rates, the county archaeologist to ask for evaluation trenching, the highway authority to ask for survey data, and environmental health to ask for a noise impact assessment where the site adjoins a road, railway or commercial use.
A holding objection stops the clock in practice even where it does not stop it formally. The cost of clearing one is usually a survey plus a technical note plus a round of meetings.
Post consent costs that belong in the same budget
Permission is the middle of the process, not the end. The items that follow are often left out of the appraisal and then land in the first year of the programme.
Condition discharge applications carry a fee per request and several conditions typically need discharging before work starts, as our note on the cost of a condition you cannot discharge sets out. A biodiversity gain plan has to be approved by the authority before development begins. Section 106 obligations bring legal costs on both sides plus monitoring fees. Community Infrastructure Levy liability crystallises on the notice served before development begins, where a charging schedule is in force.
Planning application fees themselves are set nationally, banded by number of dwellings or floorspace, and indexed annually. Check the current schedule rather than a figure from a previous appraisal.
Building the fee plan into the appraisal
Put the technical budget in the appraisal as its own cost line with a named contingency, not inside a general professional fees percentage. Three columns are enough: committed, probable and contingent, with the trigger for each contingent item stated.
That structure makes the decisions visible. If the contingent column contains trial trenching at a figure you cannot absorb, the desk based assessment becomes the most important document in the pack. If it contains an Environmental Statement, the screening opinion is the most important one.
For the narrative documents, drafting is where in-house time disappears without producing a billable output. PlanScope prices a single report at £50, with a Professional tier at £150 per month or £600 per year for unlimited reports, branding removal and a saved project library, and the pricing page sets out what each tier includes. Drafts are AI-assisted, should be reviewed before submission, and we do not guarantee planning approval. For specialist technical reports, qualified professional input may be required.
This is general guidance, not legal advice; check the position with your local planning authority or a qualified professional before relying on it.
Frequently asked questions
What counts as major development for planning purposes?
Ten or more dwellings, a residential site of 0.5 hectares or more where the number of units is not known, or 1,000m² or more of floorspace for other development. Crossing the threshold brings a 13 week determination period, wider consultation and a longer document list, including biodiversity net gain and a design and access statement.
How much should I allow for the technical pack on a major?
On a greenfield major, budgets of £50,000 and above for the full technical evidence base are normal, with transport, drainage and ecology taking the largest shares. The figure depends entirely on constraints, so price the desk studies first and treat intrusive and seasonal work as a contingent column with stated triggers.
Which surveys are season limited?
Bat emergence surveys run between May and September, with May to August optimal. Great crested newt eDNA sampling runs from 15 April to 30 June. Reptile surveys run April to October, best in spring and early autumn. Breeding bird surveys run March to August. Missing a window usually costs a year of programme rather than a survey fee.
Is an EIA screening opinion worth paying for?
Usually yes. A written negative screening opinion from the authority lets you commission the rest of the technical pack with confidence, while a positive opinion tells you early that the determination period becomes 16 weeks and an Environmental Statement prepared by competent experts is required. Scoping then narrows the chapters you pay to write.
What post consent costs should be in the appraisal?
Condition discharge fees for each application, approval of a biodiversity gain plan before development begins, legal costs and monitoring fees on the section 106 agreement, and Community Infrastructure Levy liability where a charging schedule is in force. These land in the first year of the programme and are often missing from the planning line of an appraisal.
Can AI drafted reports reduce the budget?
They reduce the cost of the narrative documents, which is where unbilled drafting time goes. PlanScope prices a single report at £50 and a Professional subscription at £150 per month or £600 per year. Drafts should be reviewed before submission, and specialist technical reports may still require qualified professional input.
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.