Walkthrough: forty eight homes on an allocated site

A major housing application evidence base is set by thresholds rather than by taste, and on an allocated site most of those thresholds are known before a line is drawn. This walkthrough follows an illustrative scheme of 48 homes on a 2.4 hectare allocation on the edge of a market town, in Flood Zone 1, with a hedgerow along the eastern boundary and an existing field access onto a classified road. Every figure in it is illustrative and used to show how the thresholds interact. The point is the sequence, because on a site of this size the programme is dictated by survey seasons and by the order in which the evidence has to be produced.

What the allocation already decided

An allocation settles the principle of residential development and usually fixes a capacity, an access point and a set of site-specific requirements. Read the policy and its supporting text line by line, then read the evidence base behind it.

On our illustrative site the allocation sets an indicative capacity of around 45 to 55 homes, requires vehicular access from the existing field entrance, requires retention of the eastern hedgerow and requires a landscape buffer to the open countryside on the north side. That last requirement costs developable area, so it goes into the layout before anything else.

What an allocation does not settle: the detailed layout, the affordable housing tenure split, the drainage solution, or whether the transport impact is acceptable. Those are still fought over.

Thresholds crossed at ten, fifty and one hectare

At 48 homes the scheme is comfortably major development. Under the Development Management Procedure Order 2015 that means 10 or more dwellings, or a site of 0.5 hectares or more where the number is not yet known, and it brings a 13 week determination period rather than eight.

Two of these deserve a second look. The site exceeds one hectare, so a flood risk assessment is needed even though the land sits in Flood Zone 1, and surface water is the real subject of that document. And 48 homes sits deliberately below 50, which is the figure at which several thresholds and consultee triggers commonly bite. Designing to sit just under a threshold is legitimate, but say so openly in the scoping request rather than hoping nobody notices.

Scoping the transport evidence

At 48 dwellings on a classified road, the honest answer is that the highway authority decides whether it wants a transport assessment or a shorter transport statement. Ask, in writing, before commissioning anything.

A reasonable scoping request sets out the proposed access geometry and visibility splays, the trip generation method and the database used, the junctions proposed for assessment, the assessment years and the sensitivity tests. Expect the authority to add a junction you did not want to model.

Traffic counts belong in neutral months. Avoid August and the second half of December, and avoid school holidays, because a count taken in half term will be challenged by the first objector who notices. On an edge of town site the walking and cycling audit matters as much as the junction capacity work, and the piece on a school expansion and the transport evidence shows how that side of the case is built.

Biodiversity net gain and the order of operations

Mandatory biodiversity net gain has applied to major development since 12 February 2024, with small sites following on 2 April 2024. The scheme must deliver at least a 10 per cent gain measured by the statutory metric, maintained for 30 years.

The sequence catches people out. The baseline habitat survey has to be done before the layout is fixed, because the metric rewards retaining what is there and punishes losing distinctive habitat. On this site the eastern hedgerow is probably the highest value feature, and a layout that puts rear gardens against it will score better than one that puts a road along it.

Then comes the arithmetic. If the on-site gain falls short, the hierarchy runs on-site first, then off-site units, then statutory credits as a last resort, and the cost rises sharply at each step.

The biodiversity gain plan is approved after permission, as a condition, which means the application needs the metric calculation and a habitat management and monitoring plan, not the gain plan itself. A biodiversity net gain assessment using the statutory metric has to be completed by a competent person under the Environment Act 2021 regime, and the metric output is only as good as the habitat classification behind it.

Protected species run on their own calendar. Bat emergence surveys run May to September, great crested newt environmental DNA sampling runs 15 April to 30 June, and reptile surveys run April to October with the best results in spring and early autumn. Miss the window and the application waits a year.

Drainage and the land the attenuation takes

Surface water drainage on a 2.4 hectare greenfield site is a land take question before it is an engineering one. Restricting discharge to the greenfield run-off rate means storing the difference, and the storage has to go somewhere that is not a plot.

Work the attenuation volume early, at a sketch level, using the greenfield run-off calculation and the current climate change allowances for the relevant river basin district. The allowances are revised periodically, so take them from the published guidance at the time of the calculation rather than from an older report.

Illustrative example: on a site of this size, a basin designed for the 1 in 100 year event plus a climate change allowance can occupy a meaningful slice of the net developable area once side slopes, freeboard and a maintenance access strip are included. Put a shape on the layout plan at the start. A drainage strategy that arrives after the layout is fixed produces either an undersized basin or a lost plot.

The lead local flood authority is a statutory consultee on surface water drainage for major development, so its standing advice and any local design guide are the documents to work to.

Affordable housing, viability and heads of terms

Above 10 units the development plan policy requirement for affordable housing applies, with the percentage and tenure split set locally. Produce the affordable housing statement as a schedule rather than a paragraph: unit numbers, bedroom sizes, tenure, distribution across the site and the proposed registered provider arrangement.

Challenge the policy figure only with evidence. A viability case on an allocated site is difficult, because the allocation was itself viability tested at plan stage, and the authority will say so. The article on how viability changed the affordable offer on a mixed use scheme sets out what a credible case looks like.

Heads of terms for the section 106 agreement should be drafted alongside the application, not after resolution to grant. On a scheme of this size expect affordable housing, education and health contributions where the local formulae apply, open space and its maintenance, highway works under section 278, travel plan monitoring and the biodiversity gain monitoring arrangements.

The pack and its programme

Working back from a target submission date, the ecology baseline and the topographic survey come first, because everything else depends on them. Transport scoping runs in parallel. Drainage follows the topographic survey. The layout iterates against all three. Heritage, arboriculture, archaeology and contamination desk studies can run alongside. The written statements are produced last, once the numbers are settled, because rewriting a planning statement around a changed layout is wasted effort.

Build in a pre-application meeting after the first layout iteration rather than before it. An officer looking at a sketch gives you a general view. An officer looking at a layout with the drainage and the hedgerow buffer already in it gives you something you can use.

Browse all 66 report types on PlanScope to assemble the evidence base for a major site.

This is general guidance, not legal advice; check the position with your local planning authority or a qualified professional before relying on it. Biodiversity net gain assessment, environmental impact assessment and land contamination work require a licensed or competent professional, and a draft is a starting point for that professional rather than a substitute.

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