Net or gross: counting units where homes are demolished

Where homes are demolished and replaced, the question of net or gross dwelling numbers in planning decides whether your scheme is a major application, whether an affordable housing policy applies, and what you pay in levy. The answers are not consistent, and that inconsistency is deliberate rather than an oversight. The definition of major development in the Town and Country Planning (Development Management Procedure) (England) Order 2015 counts the dwellings to be provided, which is a gross figure. Most adopted affordable housing policies and all housing monitoring work on net additional dwellings. The Community Infrastructure Levy works on net chargeable floorspace, not units at all.

So a proposal to demolish four flats and build twelve houses is a major application on eight net homes, and the fee, the consultation period and the determination period all follow from that.

Where the gross figure governs

Article 2 of the 2015 Order defines major development for residential schemes by the number of dwellinghouses to be provided. Twelve new houses is twelve dwellings provided, whatever stood on the site before. That classification pulls in a 13 week determination period rather than eight, a different fee band, and the publicity and consultation arrangements for major applications.

The same gross reading drives:

• the planning fee, which is calculated on the number of dwellings created
• the statutory 13 week period, and 16 weeks where the development is EIA development
• whether the application goes to committee under many schemes of delegation
• the point at which Active Travel England becomes a statutory consultee on larger residential schemes

An applicant who describes a scheme as "net gain of eight dwellings" and pays an eight-unit fee will be told the application is invalid. State both figures in the description and pay on the gross.

Where the net figure governs

Housing supply is counted net. The five year housing land supply, the Housing Delivery Test and the authority's annual monitoring report all work in net additional dwellings, because a replacement home adds nothing to the stock. That matters when you argue that a site contributes to supply: twelve houses replacing four flats contributes eight, and an officer will correct the figure if you claim otherwise.

Affordable housing is where the money is. National policy sets the affordable housing threshold by reference to major development, but the local plan policy wording is what binds, and plan wording varies. Some policies say "developments of 10 or more dwellings", some say "net additional dwellings", some say "10 or more dwellings (gross)". Read the policy, not a summary of it. Where a policy is silent, authorities generally apply the national threshold and interpret it consistently with the major development definition.

An Affordable Housing Statement should quote the policy wording verbatim, state the gross and net figures, and show the arithmetic of the contribution on the basis the policy requires. Where the two readings produce different answers, say so and explain which you have adopted.

Vacant floorspace, the existing use and the credit

Two separate mechanisms deduct the existing building, and people conflate them.

The vacant building credit in national planning guidance applies where a vacant building is brought back into use or demolished and redeveloped. Where it applies, a credit equivalent to the existing gross floorspace is set against the affordable housing contribution. It is guidance rather than a rule, it bites on floorspace not units, and authorities test whether the building was vacant in fact and whether it was deliberately emptied to engineer the credit.

The levy deduction is different and harder edged. Under the Community Infrastructure Levy Regulations 2010, the floorspace of an existing building can be deducted from the chargeable amount where the building is an in-use building, meaning a part of it has been in lawful use for a continuous period of at least six months within the three years ending on the day planning permission first permits development. Demolish early, leave the site empty for four years and then get permission, and that deduction disappears. The sequencing of demolition against the permission date is worth real money.

The thresholds that read neither way

Some triggers ignore unit counts entirely. Flood risk assessment requirements follow flood zone and site area. Transport Assessment thresholds are usually set by trip generation, floorspace or unit numbers in the local plan, and the figures PlanScope uses to flag a Transport Assessment are 50 or more units or 2,500 m² or more, with the council's own validation list and national policy taking precedence. EIA screening under the Town and Country Planning (Environmental Impact Assessment) Regulations 2017 uses site area and floorspace for urban development projects in Schedule 2, so an Environmental Impact Assessment screening opinion turns on the extent of the works rather than the net gain.

Biodiversity net gain has its own definition of a small site, framed by unit numbers and site area, and the biodiversity gain condition applies to the development permitted rather than to the uplift in homes. Where a scheme is close to any of these edges, screen it explicitly rather than inferring from the unit count.

A Statement of Community Involvement is flagged at 50 or more units in the PlanScope thresholds, again on the gross figure.

Writing the description so it cannot be misread

The description of development is the document that fixes the numbers for the life of the permission, including any later section 73 application. Write it so the gross and the net are both visible:

"Demolition of 4 no. flats and erection of 12 no. dwellinghouses with associated parking and landscaping (net increase of 8 dwellings)."

That form survives scrutiny. It tells the fee team the gross, it tells the monitoring officer the net, and it gives you a defensible position when the affordable housing policy is applied. Avoid "redevelopment to provide 12 units", which hides the demolition, and avoid "8 new homes", which understates what is being built.

Illustrative example

A site holds two semi-detached houses in poor condition. The scheme demolishes both and builds nine flats and two houses, eleven dwellings in total, a net gain of nine. The application is major on the gross figure of eleven, so the fee follows the major band and the period is 13 weeks. The local plan affordable housing policy is expressed as "schemes of 10 or more net additional dwellings", so on nine net the policy threshold is not crossed and no affordable provision is sought. The levy calculation deducts the floorspace of the two houses because both were occupied until three months before the permission was issued. Change one fact, leaving the houses empty for four years before applying, and the levy liability rises by the full deduction. This example is illustrative and is not based on a decided application.

Disputes that surface at validation

Validation officers are checking arithmetic against a checklist, and the recurring arguments are predictable. Whether a subdivided house counted as one dwelling or two. Whether an outbuilding in residential use was ever a lawful dwelling. Whether a building that burned down still counts for deduction purposes. Whether a block of bedsits was one planning unit or several.

Each of those is an evidence question, and the evidence is council tax records, tenancy agreements, utility accounts, historic planning permissions and the authority's own records. Assemble it before you submit, because arguing it after an invalidity notice costs weeks. Where the lawfulness of the existing use is in real doubt, a certificate of lawful existing use or development under section 191 of the Town and Country Planning Act 1990 settles it properly.

And be consistent. A scheme described one way in the Planning Statement, another way in the levy form and a third way on the drawings gives the authority a reason to send everything back.

Enter the site postcode on PlanScope to see which report types the constraints and the scale of a demolition and rebuild scheme are likely to trigger. Start from the home page.

This is general guidance, not legal advice. Check the position with your local planning authority or a qualified professional before relying on it. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.