Five dwellings: where policy thresholds begin to bite

A scheme of five dwellings sits in an awkward gap. It is too big to be treated as an infill plot and too small to be a major application, so none of the headline thresholds apply, and yet the evidence base is noticeably heavier than it is for a single house. Major development in England starts at 10 or more dwellings, or a site of 0.5 hectares or more where the number is not known. Five units stays below that line, which is the single most useful fact to hold onto when a consultant proposes a report you may not need.

What does apply at five units is a different set: mandatory biodiversity net gain, a levy liability with no small-site relief, drainage expectations that scale with impermeable area, and local parking standards that bite harder on a shared access than on a single drive.

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

Which requirements apply from the first dwelling

Several obligations do not scale at all. They attach to the first new dwelling and are the same at five.

• A location plan, site plan, elevations and floor plans to the national validation requirements.
• A design and access statement where the site is in a conservation area or World Heritage Site and the floorspace exceeds the stated threshold, and in most other cases because the authority's local list asks for one.
• Biodiversity net gain of 10 per cent, unless an exemption applies.
• The planning fee, charged per dwelling for schemes up to 50 dwellings.
• Ownership certificates and, where relevant, notice to other owners and agricultural tenants.
• A flood risk assessment where the site is in Flood Zone 2 or 3, or is one hectare or more in Flood Zone 1.

The last of those surprises people. Flood zone, not scheme size, is the trigger, so a single plot in Zone 3 carries a Flood Risk Assessment that a five unit scheme in Zone 1 on a small site does not.

What a five unit scheme typically adds

Beyond the baseline, the documents a five unit scheme usually attracts are driven by the site rather than the unit count: an ecology appraisal, an arboricultural report where trees are affected, a drainage strategy, and a transport statement where the access is new or altered.

None of those is triggered by reaching five. All of them are triggered by what is on the land. The practical consequence is that two five unit schemes a mile apart can have very different evidence bases, and copying a neighbour's document list is a poor way to scope.

Affordable housing is the exception that does turn on number. The national position is that affordable housing contributions should not be sought from developments of fewer than 10 homes, but in designated rural areas authorities may apply a lower threshold, and that lower threshold is commonly set at five. If your site sits in a designated rural area, check the adopted plan before assuming nothing is payable, and if a contribution is sought, an Affordable Housing Statement is the document that sets out the position.

Drainage and surface water expectations at this size

The lead local flood authority is a statutory consultee on major development, so a five unit scheme does not automatically go to them. That does not mean drainage is unexamined. The authority will still expect surface water to be managed on site where ground conditions allow, and a condition requiring approval of a drainage scheme is close to standard on any scheme creating new roofs and hardstanding.

What changes at five units is that the roof and hardstanding area usually passes the point where soakaways alone are straightforward. You are into attenuation, flow control and a discharge agreement with the sewerage undertaker if infiltration fails.

Do the infiltration testing before you fix the layout. A failed percolation test discovered after approval leaves you looking for attenuation volume in a layout that has none, and the drainage strategy then has to be redrawn rather than written. Schedule 3 of the Flood and Water Management Act 2010, which would introduce a separate SuDS approval regime, has not been brought into force, so approval still runs through the planning condition route. Verify the current position before relying on it.

Biodiversity gain obligations on a small site

Mandatory biodiversity net gain applied to major development from 12 February 2024 and to small sites from 2 April 2024. A five unit scheme is a small site, which means the small sites metric is available and the survey burden is lighter, but the 10 per cent obligation and the 30 year management period are identical to a major scheme.

The exemptions worth checking are the de minimis threshold, which covers development affecting less than 25 square metres of on-site habitat and less than five metres of on-site hedgerow, the self-build and custom build exemption for up to nine dwellings on a site of no more than 0.5 hectares, and householder development. Self-build is the one that most often applies to a small group of plots, and it has conditions attached about the nature of the scheme, so read them rather than assuming.

Where no exemption applies, the gain plan has to be approved before development begins. A Biodiversity Net Gain Assessment prepared by a competent person is what the Environment Act 2021 regime expects, and a draft is a starting point for that person rather than a substitute. For specialist technical reports, qualified professional input may be required.

Parking and highway standards

Five dwellings sharing a single access is the point at which the highway authority starts asking about visibility splays, turning provision and refuse vehicle access rather than only whether a car can leave in forward gear.

The questions that recur:

• Can a refuse vehicle reach within the collection distance the authority specifies, or is a bin collection point needed at the highway edge?
• Does the access geometry meet the visibility standard for the recorded speed of the road, measured rather than assumed from the limit?
• Is parking provided at the adopted standard per bedroom count, including any visitor allowance?
• Is there turning space inside the site so vehicles do not reverse onto the carriageway?

A Transport Statement is usually proportionate at this scale. The threshold at which a full Transport Assessment is expected is far higher, commonly 50 or more dwellings or 2,500 square metres of floorspace, so pushing back on a request for one at five units is reasonable where the access is not unusual.

Levy liability and available relief

The Community Infrastructure Levy, where the authority has adopted a charging schedule, is charged on new build floorspace. Five dwellings will almost always exceed the 100 square metre minor development threshold, so the exemption that protects small extensions is not available.

Relief that may be: self-build relief for a dwelling built by or on behalf of the person who will occupy it as a main residence, residential annexe and extension exemptions, and social housing relief. Every one of them has to be claimed on the correct form before development begins, and self-build relief carries a three year clawback period and further forms after completion.

Miss that notice and the relief is lost, with no discretion in most cases. That is a harsh outcome for a self-builder and the single administrative failure worth setting a reminder for.

Charging schedules are indexed annually. Check the current schedule and the current index figure on the charging authority's website rather than working from a rate quoted in an older appraisal.

Assembling a proportionate application

Start from the constraints, not from a template list. Pull the flood zone, the designations, the tree cover and the highway record first, then decide which reports the site actually calls for. At five units the right answer is usually six to nine documents, and an authority asking for more should be able to point to the line in its local validation list that requires each one.

Two related points sit alongside this: how energy and carbon requirements change by scheme scale, and when drainage needs lead local flood authority approval.

PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.