Replacement dwelling planning permission: policy tests

Demolishing a house and rebuilding it is not an extension. Replacement dwelling planning permission is granted on a full application for a new dwelling, not a householder application, and the council assesses it against the policies that apply to new housing on that plot. That reclassification is what catches self-builders out. The fee band changes, the validation list lengthens, mandatory biodiversity net gain applies, and on a Green Belt or open countryside site you have to justify the principle of a house all over again.

What follows is the sequence of tests an officer will work through, and the evidence that answers each one.

Why a rebuild is treated as a new dwelling

Demolition plus new build is development under section 55 of the Town and Country Planning Act 1990. Because the end result is a dwellinghouse rather than an alteration to one, the application is a full application for one dwelling: a minor application, an eight-week determination period, and the higher fee band for new dwellings. Planning fees are indexed annually from 1 April, so check the current schedule on the Planning Portal before you submit.

The first substantive question is whether the existing dwelling is lawful and whether its residential use survives. If the house has been derelict for years, an officer may argue the residential use has been abandoned, in which case the fall-back position disappears and your scheme is judged as a wholly new house in that location. The courts have looked at four factors when deciding abandonment: the physical condition of the building, how long it has been out of use, whether any other use has intervened, and the owner's intentions. If the building is roofless, gutted or has been used as a store for a decade, get advice before assuming a replacement is a formality.

Demolition itself needs thought. In a conservation area, demolishing a building is "relevant demolition" and needs planning permission in its own right, which in practice means the demolition is described in your application. Outside designated areas, demolition of a dwellinghouse is normally covered by permitted development rights in the GPDO 2015 Schedule 2 Part 11, subject to prior approval of the method of demolition and site restoration. Ask your local planning authority which route it expects, because validation officers vary on whether they want demolition inside the red line or handled separately.

Volume, footprint and the "materially larger" wording

Most adopted local plans carry a replacement dwellings policy with a numeric ceiling. The measure differs: some plans limit the increase in volume over the original dwelling, others control footprint, others use gross internal floorspace, and rural plans often combine a volume cap with a requirement that the new house sits within or close to the existing footprint. There is no national figure. Read the policy, then read the supporting text and any householder or rural design supplementary planning document, because that is where the measurement conventions live.

Two details decide most arguments.

First, "original" usually means the dwelling as first built, or as it stood at 1 July 1948, not as extended since. A 1950s cottage with three later extensions may have a much smaller policy baseline than the building you are about to knock down. Second, volume is normally measured externally and includes roof volume, so a modest footprint increase paired with a higher ridge and a habitable roof can blow through a volume cap without looking bigger on plan.

Produce that comparison yourself and put it in the Planning Statement rather than leaving the officer to measure your drawings. Where you exceed the local ceiling, say so openly and argue the case on design, energy performance and amenity improvement. An unacknowledged breach reads as an attempt to slip something past.

Green Belt replacement buildings and openness

In the Green Belt, the relevant exception is the replacement of a building provided the new building is in the same use and not materially larger than the one it replaces, at NPPF (December 2024) paragraph 154(d). Meet it and the development is not inappropriate, so you avoid having to demonstrate very special circumstances.

"Materially larger" is a planning judgement, not a percentage. Volume is the usual yardstick, and inspectors have generally treated increases of a few per cent as immaterial and substantial uplifts as fatal, but the assessment also takes in footprint, height, bulk and the spread of the building across the plot. A replacement that stays within the volume of the original while sprawling wider and closer to a road can still harm openness, which is assessed spatially and visually.

Be careful with two related points. Outbuildings and later extensions are not always counted towards the building being replaced, and the December 2024 Framework's grey belt provisions are aimed at a different problem; a like-for-like replacement should not need them. In a National Landscape or National Park, the additional test is landscape and scenic beauty, which usually means a materials and roofscape argument supported by photographs from public vantage points rather than a volume argument alone.

Outside the Green Belt, in genuinely open countryside, the isolated homes exceptions at NPPF (December 2024) paragraph 84 do not include a general right to replace a dwelling, so the principle rests on your adopted plan's replacement dwellings policy. If the plan has no such policy, that is a problem to identify at pre-application stage, not after refusal.

Biodiversity net gain and the demolition baseline

Mandatory biodiversity net gain applies to most planning permissions in England, from 12 February 2024 for major development and 2 April 2024 for small sites. A replacement dwelling is not a householder application, so the householder exemption does not help you. Two exemptions might: the de minimis exemption where the development affects less than 25 m² of onsite habitat and less than 5 m of linear habitat, and the self-build and custom housebuilding exemption for schemes of no more than nine dwellings on a site of no more than 0.5 hectares that consist exclusively of self-build or custom-build dwellings. Check whether you qualify before commissioning anything.

If you are caught, the baseline is where replacement schemes go wrong. The house you are demolishing scores nothing: buildings and sealed surfaces carry no biodiversity units in the statutory metric. The garden does score. Lawn, hedgerows, scrub, orchard trees and any semi-improved grassland all generate units, and a bigger footprint plus a wider driveway and turning head eats into exactly those habitats. So the demolition is neutral and the landscaping is where your 10 per cent uplift is won or lost.

The other trap is timing. If habitat is cleared or degraded without permission before the application, the pre-development value can be assessed as at 30 January 2020 instead of the date of application. Grubbing out a hedge or scraping the garden ahead of a survey does not reduce your obligation; it can increase it and hand the council an enforcement issue.

The statutory metric must be completed by a competent person, and the biodiversity gain plan is approved by the local planning authority after permission under the pre-commencement biodiversity gain condition. Residential schemes of one to nine units on sites under one hectare with no priority habitat can normally use the small sites metric, which is quicker and cheaper. A Biodiversity Net Gain Assessment draft can structure the argument and set out habitat parcels and the 30-year management position, but the metric itself and any habitat condition assessment need a suitably qualified ecologist. That is a legal expectation under the Environment Act 2021 regime, not a preference.

Bats matter more on replacement schemes than on almost any other householder-scale project, because you are removing an entire roof void. A preliminary roost assessment can be done at any time of year. Emergence and re-entry surveys run May to September, with May to August optimal under the Bat Conservation Trust Good Practice Guidelines (4th edition, 2023). If a roost is present, mitigation and a Natural England licence require a licensed ecologist under the Conservation of Habitats and Species Regulations 2017. Miss the season and you lose a year.

Drainage, contamination and asbestos evidence

Check the Environment Agency Flood Map for Planning first. A site in Flood Zone 2 or 3, or of one hectare or more, needs a Flood Risk Assessment treated as a site-specific document with finished floor levels, climate change allowances from the current Environment Agency schedule, and the sequential test where the zone requires it. Replacement dwellings in flood zones often turn on whether the new floor level is raised and whether the footprint is more vulnerable than the one it replaces.

Surface water is the other recurring condition. Demolishing a house with soakaways or a direct connection and rebuilding with a larger roof and more hardstanding changes run-off, and lead local flood authorities increasingly ask for a drainage strategy with infiltration testing rather than a note on the block plan.

On contamination, older rural plots frequently carry buried oil tanks, asbestos cement outbuildings, made ground or filled ponds. A Phase 1 desk study is the standard planning-stage document and, where the NPPF places responsibility on the developer, councils expect it prepared in accordance with BS 10175 by suitably qualified and experienced persons. Asbestos in the building you are demolishing is a separate matter under the Control of Asbestos Regulations 2012: a refurbishment and demolition survey is a health and safety requirement, not a planning one, but the two programmes have to line up because you cannot start demolition without it.

The CIL offset for existing floorspace

Where your council has a Community Infrastructure Levy charging schedule, a replacement dwelling can be much cheaper than a new build on a bare plot, because the floorspace of the building being demolished may be deducted from the chargeable area. Under the Community Infrastructure Levy Regulations 2010 the deduction only applies to an "in-use building", which broadly means a building that 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.

That wording has real consequences. Demolish early, or buy a house that has stood empty for four years, and the offset can vanish. If the offset is worth having, keep the building standing and, where you can, keep it lawfully occupied until permission is issued, and keep evidence such as council tax and utility records.

Self-builders should also look at the CIL self-build exemption, which requires Form 7 Part 1 to be submitted and acknowledged before commencement, Form 7 Part 2 within six months of completion, and occupation as your sole or main residence for three years. Miss a form or a deadline and the full charge becomes payable. Rates and instalment policies are set locally and reviewed, so read the council's current charging schedule.

Programme and the submission pack

A realistic order of operations for a single replacement dwelling:

1. Confirm the lawful residential use and read the replacement dwellings policy in the adopted local plan, plus any relevant design SPD.
2. Book the preliminary roost assessment and tree survey early; both can be done outside the summer, and both can trigger seasonal work.
3. Request pre-application advice with your volume and footprint comparison already drawn up, so the officer responds to numbers rather than a concept.
4. Commission the ecologist's baseline and metric, the Phase 1 desk study and the drainage work in parallel.
5. Prepare the narrative documents last, once the technical answers exist.
6. Check the council's local validation list line by line, then submit.
7. Budget time after permission for the biodiversity gain plan, drainage details and construction management conditions before you can lawfully start.

On the narrative side, a Design and Access Statement is a statutory requirement under the DMPO 2015 for one or more dwellings in a conservation area or World Heritage Site, and for major development. For a single replacement house elsewhere it is not compulsory, though most councils welcome one and it is the natural place to explain the design response to the building being lost. Tree constraints under BS 5837:2012, a construction management plan for a narrow lane, and a structural survey where you are arguing the existing building cannot reasonably be repaired all earn their place in the pack.

Enter your postcode on PlanScope to see which reports a replacement dwelling site is likely to need, and which of them a professional has to sign.

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. For specialist technical reports, including the biodiversity metric, contamination assessment and protected species work described above, qualified professional input is required.