Documents for a replacement dwelling in the Green Belt
A Green Belt replacement dwelling turns on whether the new house is materially larger than the one it replaces. The pack has to prove that with measurements, not assertions.
A replacement dwelling in the Green Belt is not inappropriate development provided the new building is in the same use and not materially larger than the one it replaces. That single test decides most of these applications, and the document pack exists to answer it with measurements. Green Belt replacement dwelling documents that lead with design intent and treat the volume comparison as an appendix get refused, because the case officer's first task is arithmetic.
Two further things have to be true. The existing building has to be a dwelling in lawful residential use, and it has to still exist. A demolished house is not a building capable of replacement, and a long-abandoned one may have lost its residential use altogether.
The policy test and what "materially larger" means
National policy gives the exception without defining a percentage. Many authorities fill the gap in a supplementary planning document or a development management policy, setting a figure for the maximum uplift in volume or floorspace, commonly somewhere between 10 and 40 per cent depending on the authority. Some set no figure at all and assess materiality case by case against openness.
So the first document to read is the adopted local plan policy and any supporting guidance, and the figure to design to is theirs rather than a national rule of thumb. Where the authority has no stated threshold, expect the assessment to run on volume, footprint, height, siting and visual prominence together, and expect the openness argument to matter more.
| What is compared | Why it matters | How to present it |
|---|---|---|
| External volume | The usual basis of the materially larger test | Measured, with the method stated |
| Footprint | Affects openness at ground level | Overlay drawing, existing and proposed |
| Height and ridge line | Visual prominence in the landscape | Elevational comparison, same scale |
| Siting within the plot | Can improve or worsen openness | Site plan with both positions |
| Domestic curtilage and outbuildings | Cumulative spread of built form | Schedule of all structures |
Measuring and evidencing the existing building
This is where applications fail on evidence rather than on policy. Commission a measured survey of the existing house before anything else. Not a tape measure exercise, an actual survey with plans, sections and elevations, so the volume can be calculated from dimensioned drawings that the officer can check.
State the volume calculation method explicitly. External volume measured to the outer face of external walls and to the underside of the roof covering, including or excluding integral garages, roof voids and below-ground space, with each decision stated. Two competent surveyors can produce volumes 10 per cent apart on the same house purely through different conventions, and an unexplained figure invites the officer to use the least favourable interpretation.
Include the planning history. Extensions built under permitted development count as part of the existing building for comparison purposes in most authorities' guidance, but some measure against the original dwelling. Check which, because on a house extended twice since the 1980s the difference is decisive.
Where any part of the house is in poor condition, resist the temptation to describe it as beyond repair unless a structural report says so. A structural appraisal supports a demolition case. An estate agent's opinion does not.
Volume and footprint comparison drawings
Produce a dedicated comparison drawing rather than leaving the officer to work it out. What it should contain: existing and proposed footprints overlaid in contrasting line weights on the same site plan, a volume schedule broken down by element, existing and proposed elevations at the same scale on one sheet, and a summary table giving the percentage change in volume, footprint and ridge height.
Put the percentage figures in the planning statement as well. An officer's committee report or delegated report will quote a number, and it is better that the number is yours and is explained.
Landscape and openness evidence
Volume is the threshold test, but openness is what the policy protects, and the two can point in different directions. A replacement that is 15 per cent larger in volume but sited further from the lane, lower in the plot and with two outbuildings removed can improve openness. That argument needs evidence.
For a prominent site, or one within a National Landscape as well as the Green Belt, a Landscape and Visual Impact Assessment prepared to GLVIA3 principles gives the assessment structure: identify receptors, describe the baseline, then assess effects at year one and after mitigation establishes. For a modest site in an enclosed setting, a shorter landscape appraisal with annotated photographs from the public vantage points is usually proportionate. Include a photograph from every point where the public can see the house, and say where each was taken from.
Ecology in and around an old building
An old rural dwelling is potential bat roost habitat, and demolition without a survey is a criminal risk rather than a planning one. A Preliminary Ecological Appraisal with a preliminary roost assessment is the starting point, and where evidence or potential is found, emergence and re-entry surveys are needed in the survey season, generally May to September with the optimal window May to August.
That seasonality is the single biggest programme risk on these applications. A decision to demolish taken in October can mean waiting until the following May.
Bat work and any Protected Species Survey must be carried out by a suitably licensed ecologist under the Wildlife and Countryside Act 1981 and the Conservation of Habitats and Species Regulations 2017, and any mitigation licence is theirs to obtain. An AI-assisted draft can frame the report and its policy context; it cannot do the survey or hold the licence.
Biodiversity net gain also needs checking. A replacement dwelling submitted as a full application may fall within the mandatory regime under the Environment Act 2021 unless an exemption applies, and a Biodiversity Net Gain Assessment using the statutory metric has to be completed by a competent person, with the biodiversity gain plan approved by the authority. Confirm the exemption position with the case officer early rather than assuming.
Drainage, access and the pack that answers the test
Rural plots bring two practical evidence requirements. Foul drainage where there is no mains connection, which means percolation testing and a package treatment plant or septic tank specification, with the discharge position and any environmental permit requirement identified. And access, where the replacement is an opportunity for the highway authority to ask for visibility splays that the existing access does not have.
The pack that answers the policy test:
- Measured survey of the existing dwelling with the volume method stated.
- Volume, footprint and height comparison drawings and a summary percentage table.
- Planning statement setting out the materially larger test against the adopted policy figure.
- Landscape appraisal or LVIA with photographs from public vantage points.
- Preliminary ecological appraisal, with bat emergence surveys where triggered.
- Biodiversity net gain position, with metric and gain plan where the regime applies.
- Foul drainage and access details.
For a demolition and rebuild outside the Green Belt the constraints are different and the pack is lighter, as set out in reports for demolition and rebuild of one house.
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, qualified professional input may be required: protected species work requires a suitably licensed ecologist and the statutory biodiversity metric requires a competent person. This is general guidance, not legal advice; check the position with your local planning authority or a qualified professional before relying on it.
Frequently asked questions
How much larger can a Green Belt replacement dwelling be?
National policy says not materially larger without setting a percentage. Many authorities publish a figure in a supplementary planning document or development management policy, often between 10 and 40 per cent in volume terms. Read the adopted policy for your authority and design to that figure rather than to a general rule of thumb.
Is volume or floor area used for the comparison?
External volume is the usual basis, though some authorities assess floorspace, footprint and height as well. State your calculation method in the submission: whether measurements are to the outer face of walls, whether roof voids, integral garages and below-ground space are included. Unexplained figures invite the least favourable interpretation.
Does a demolished house still count as a building for replacement?
No. The exception applies to replacing an existing building, so a house already demolished cannot be replaced under that policy. A long-abandoned dwelling may also have lost its lawful residential use. Where use is in doubt, a lawful development certificate is the formal route to establish the position.
Do bat surveys delay a replacement dwelling application?
They can. A preliminary roost assessment is possible at any time of year, but emergence and re-entry surveys generally need the season from May to September, with May to August optimal. Where potential is found in autumn, the survey may not be possible until the following spring, so commission the appraisal early.
Does biodiversity net gain apply to a replacement dwelling?
Often yes, because a replacement dwelling is usually a full application rather than a householder one, and the mandatory regime under the Environment Act 2021 applies unless an exemption such as the de minimis threshold is met. Confirm the position with the case officer before assuming an exemption applies.
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.