Five dwellings on a brownfield infill plot
Below ten units nothing is major, so the exercise is proportionality. This illustrative walkthrough shows which parts of the evidence base a five dwelling scheme actually needed.
A five dwelling scheme sits below every major development threshold, and that is the single most useful fact about it. Ten units is where major status, the affordable housing policy threshold and the heavier evidence requirements arrive, so a small site planning application example at five units is an exercise in proportionality: working out which parts of the evidence base the authority's validation list actually requires at that scale, and declining politely to produce the rest.
What follows is an illustrative composite rather than a real project. The figures, the site and the sequence are illustrative, and no real authority or decision is described.
The site and the policy position
A 0.28 hectare former builders' yard inside a settlement boundary, with a single access onto an unclassified road, bounded by rear gardens on two sides and a hedgerow on the third. Previously developed land, unallocated, with no heritage or landscape designation and no part in flood zone 2 or 3.
The policy position is as good as a small site gets. Inside the boundary, brownfield, in a plan with a housing supply policy that supports infill. The design policy and the amenity policy are the ones that do the work, and the amenity policy is the one with the numbers in its supporting text.
Five units on 0.28 hectares is about 18 dwellings per hectare, which is low for an urban infill site, and the first question the officer asked at pre-application was whether the site could take more. That is worth anticipating. A density below the local pattern invites a policy argument about efficient use of land, and the answer has to be about the constraints rather than about the preferences of the developer.
Which documents the validation list required
The authority's local list, taken from its website on the day of submission, produced this set for a minor residential application on previously developed land.
| Document | Why it was required | Scale of the work |
|---|---|---|
| Planning Statement | Policy compliance, standard requirement | A short document, policy by policy |
| Site and location plans, floor plans, elevations | National requirement | The main cost |
| Land Contamination Phase 1 | Previously developed land, former yard use | Desk study by a qualified person |
| Preliminary Ecological Appraisal | Hedgerow and buildings on site | A single ecologist visit |
| Biodiversity net gain information | National requirement since 2024 | Metric plus a gain plan commitment |
| Drainage strategy | Surface water from a hard-surfaced site | Infiltration testing plus a design |
| Tree survey | Hedgerow and two boundary trees | BS 5837 survey of the affected stock |
| Transport Statement | Access onto an unclassified road | A short statement, not an assessment |
No Design and Access Statement was required, because the site is not in a conservation area and the scheme is not major development. No affordable housing statement, because the policy threshold is ten units. No viability assessment, because there was nothing to test.
The temptation on a small site is to submit more than the list asks for, on the theory that it looks thorough. It does not. It gives the officer more documents to consult on and more chances for a consultee to ask a question.
Ecology and the net gain position
The ecologist's appraisal found no roosting features in the single-storey yard buildings, a species-poor hedgerow of moderate value, and no evidence of protected species. That is the ordinary outcome on a hard-surfaced urban site and it kept the ecology cost down.
Biodiversity net gain was the item that needed real thought. Since April 2024 the mandatory regime applies to small sites, requiring a 10 per cent gain secured for 30 years through a biodiversity gain plan approved by the authority. The statutory metric has to be completed by a competent person, which is a legal requirement rather than a recommendation.
Two things made it workable here. A baseline dominated by hard standing scores low, so the gain is easier to achieve on site than it would be on a grassland site. And retaining the hedgerow and enhancing it, rather than removing and replacing it, avoided the loss that drives most off-site unit purchases.
The de minimis exemption, which applies where development affects less than 25 square metres of on-site habitat and less than 5 metres of linear habitat, did not apply because the hedgerow was within the works area. Check it on every small site, because it is the difference between a metric exercise and none.
Drainage and the infiltration testing
The site was almost entirely sealed, so the discharge rate from the developed site could be shown to be lower than the existing rate. That is the strongest drainage position available on a brownfield site and it should be stated in the first paragraph of the strategy.
Infiltration testing was carried out to the established soakaway test method, in trial pits at the proposed soakaway positions and at the proposed formation depth, which is the detail most reports get wrong by testing at a convenient depth instead. Two of three pits gave usable rates and the third hit made ground, which changed the layout of the drainage rather than the layout of the houses.
The lead local flood authority consulted on the strategy and asked for a maintenance plan and an exceedance route. Both are quick to add before submission and tedious to add afterwards.
Highways access and visibility
Visibility was the issue that nearly reduced the scheme to four units. The access onto the unclassified road needed a splay based on the stopping sight distance for the road's speed, derived using the approach in Manual for Streets rather than taken from a table, and the hedgerow on the northern boundary sat inside the required splay.
Three options were tested: reduce the hedge within the splay and maintain it by condition, move the access 8 metres north where the alignment was straighter, or reduce to four units and use the existing access unchanged. The second worked, at the cost of one plot's garden depth.
Parking followed the local standard, with the cycle storage shown as a structure on the plan rather than as a note, which is what the highway authority asked for.
Section 106 heads of terms
Below ten units there was no affordable housing requirement and no education contribution under the authority's published approach. What remained was a contribution towards off-site open space, calculated from the published formula, and a monitoring fee.
The useful point for the next site is that a five unit scheme can often be delivered with a unilateral undertaking rather than a bilateral agreement, which cuts several weeks and a good deal of legal cost out of the programme. Ask the authority early whether it will accept one.
The committee report and the decision
The application was determined under delegated powers, because the number of objections fell below the referral trigger in the scheme of delegation and the officer recommendation was for approval. Conditions covered the drainage details, the biodiversity gain plan, the hedgerow retention and maintenance within the visibility splay, materials, and the contamination remediation strategy.
Determination took a little over the eight week period, with a short extension of time agreed in writing when the drainage consultee response arrived late. Agreeing that extension rather than letting the period expire preserved the application and cost nothing.
The lesson that generalises is about sequencing rather than content. The infiltration testing and the ecology visit both had to happen before the layout was fixed, and both were commissioned after the layout was drawn. That cost a redesign.
What to take to the next small site
- Get the local list on the day you start, not the day you submit
- Commission infiltration testing and the ecology appraisal before the layout is fixed
- Check the biodiversity net gain de minimis exemption first, then the metric
- Test the visibility splay against the actual boundary vegetation before counting plots
- Ask whether a unilateral undertaking is acceptable
- Agree an extension of time in writing rather than allowing the determination period to run out
The documents involved are listed by category on the report types index, and contamination found later rather than earlier is a separate and more expensive problem, as a conversion where contamination was found mid-build shows. Where a party wall is involved in the construction phase, the notice periods can govern the programme, as a party wall notice that delayed a rear extension programme describes.
Enter your postcode on PlanScope to see which of the 66 reports a small site like this is likely to need.
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 changes at ten units?
Major development status arrives, bringing a 13 week determination period, and the affordable housing policy threshold is usually reached, requiring an affordable housing statement and often a viability discussion. Statutory consultation and publicity requirements increase, and the biodiversity net gain regime applies in its major rather than small site form. Below ten, the evidence base should be proportionate.
Does biodiversity net gain apply to a five unit scheme?
Yes, the mandatory regime has applied to small sites since April 2024, requiring a 10 per cent gain secured for 30 years through a biodiversity gain plan approved by the authority. The statutory metric must be completed by a competent person. Check the de minimis exemption first, which applies below 25 square metres of on-site habitat and 5 metres of linear habitat.
Do I need a Design and Access Statement for five houses?
Usually not. A statement is required for major development and for schemes in a conservation area or World Heritage Site involving one or more dwellings or significant floorspace, and for listed building consent. Outside those situations a minor residential application does not need one, and submitting extra documents gives consultees more to question.
Why does infiltration testing have to come before the layout?
Because the results can move the drainage, and the drainage can move the houses. Testing should be done in trial pits at the proposed soakaway positions and at the proposed formation depth, not at a convenient depth, and made ground or a high water table can rule out infiltration in part of the site. Commissioning it after the layout is drawn tends to cost a redesign.
Can a small scheme avoid a bilateral section 106 agreement?
Often, yes. Where the obligations are limited to a contribution and a monitoring fee, many authorities will accept a unilateral undertaking from the landowner, which removes the authority's legal team from the drafting chain and can save several weeks. Ask early, because the answer depends on the authority's own practice rather than on the law.
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.