Walkthrough: a single self-build plot on a garden site

One house in a long back garden is the most common self-build project in England and one of the most frequently refused. The reason is rarely the house. It is the access past the existing dwelling, the relationship between the two gardens, and the trees on the boundary that nobody surveyed until the officer asked. This walkthrough follows an illustrative application for a single detached house on the rear third of a 1930s semi-detached plot, and sets out what went into the submission and what came back as conditions. It is an illustrative example, not a real decision.

The plot is 9 metres wide and 34 metres deep, with a 3.2 metre wide strip alongside the host dwelling giving access to the street.

The plot and its relationship to the host dwelling

The application splits the garden at a point 14 metres behind the rear wall of the host house, leaving that dwelling with a garden of reasonable depth and creating a plot of roughly 230 square metres for the new house. The new dwelling is a two-bedroom house with a shallow pitched roof, positioned to sit against the rear boundary rather than in the middle of the plot.

Two early decisions shaped everything else. The new house faces across its own garden rather than towards the host dwelling, which removed most of the overlooking problem. And the ridge was kept below the ridge of the neighbouring bungalow, which removed the argument about scale in the street's rear gardens.

Residential gardens are not previously developed land for the purposes of national policy, so the usual brownfield arguments were unavailable. The case had to stand on character, amenity and the location's accessibility.

Backland and garden development policy

Most adopted local plans carry a policy on infill and backland development, and it usually turns on three tests: whether the pattern of development in the area can absorb the plot, whether amenity for existing and future occupiers is acceptable, and whether access is safe.

The Planning Statement addressed them in that order, with a survey of the surrounding block showing two earlier backland approvals on the same street. That evidence did the heavy lifting, because a plot that is the first of its kind in an area of unbroken rear gardens is a much harder case than one following an established pattern.

Where an authority has a householder design guide or a residential design supplementary document, read it before drawing anything. Those documents contain the separation distances and garden size standards the officer will apply.

Access arrangements past the existing house

The access strip is where backland schemes fail. At 3.2 metres, the drive was wide enough for a single vehicle but not for two to pass, and the highway authority wanted visibility at the footway, a turning arrangement so vehicles could leave in forward gear, and confirmation that the host dwelling retained its own parking.

The submission dealt with each point separately:

1. Visibility splays at the back of the footway, drawn on the site plan with the boundary wall reduced in height for the first two metres.
2. A turning head within the new plot, with a tracking drawing for a car and for a refuse vehicle at the street.
3. Two retained parking spaces for the host dwelling, shown dimensioned.
4. Bin storage within a carrying distance the collection authority accepts, with the presentation point at the street.
5. A note on construction access, because a 3.2 metre drive cannot take a concrete wagon without protection to the host house.

Approved Document H of the Building Regulations sets out expectations for waste storage and carrying distances, and the collection authority usually has its own standard on top. Ask before you draw the bin store.

Overlooking and amenity for both dwellings

Many authorities apply a back-to-back separation guide of around 21 metres between facing habitable room windows, and a shorter distance to a blank flank wall. These are rules of thumb rather than policy, and they vary, so check the local document.

In this case the achieved separation between the rear of the host house and the front of the new house was 19 metres, slightly under the guide. The design response was to place the new dwelling's kitchen and bathroom on that elevation, with the living space and bedrooms facing the rear garden, and to accept obscure glazing by condition on the two upper windows facing the host dwelling. Sometimes the honest answer to a separation shortfall is a plan change, not a screen.

Garden sizes for both dwellings were stated on the drawings against the local standard. Where a scheme leaves the host dwelling with less garden than the standard allows for a house of that size, expect a refusal on that ground alone.

Trees on the boundary and root protection

Three mature trees stood on the rear and side boundaries, two of them in a neighbour's ownership. A survey to BS 5837:2012 classified them and produced root protection areas, calculated as a radius of 12 times the stem diameter for single-stemmed trees, with the area capped for the largest.

The root protection area of the largest tree covered part of the proposed footprint. Rather than seek to remove a tree in someone else's garden, the footprint was reduced by 1.2 metres and a no-dig construction was specified for the parking area within the protection zone. The tree survey and the tree protection plan went in with the application, and the arboricultural method statement followed as a condition.

Check for a Tree Preservation Order and for conservation area status before designing. In a conservation area, six weeks notice is needed for works to trees, whether or not an Order exists.

Drainage and utilities to the new plot

Foul drainage connected to the existing sewer in the street rather than through the host dwelling's private drain, which avoided an easement negotiation with a property that was being sold. Surface water went to a soakaway within the plot after infiltration testing, with a small permeable paved area to the drive.

Utilities crossing the host garden needed easements recorded in the transfer, and the electricity connection required a quotation from the distribution network operator with a lead time longer than the planning determination period. Order those early; they are not planning matters but they sit on the critical path.

Biodiversity net gain deserves a specific check on a plot like this. Exemptions exist, including one for self-build and custom housebuilding of nine dwellings or fewer on sites under half a hectare, and a threshold for development affecting only a very small area of on-site habitat. Whether a particular plot qualifies depends on the regulations and on how the scheme is delivered, so confirm it rather than assuming either way.

The submitted pack in full

• Application forms and the correct fee for one dwelling, with the ownership certificate.
• Location plan with the site edged red and the host dwelling's remaining land edged blue.
• Existing and proposed site plans showing both dwellings, gardens, parking and bin storage.
• Floor plans, elevations and a section showing levels against the boundary.
• Planning Statement covering the backland policy tests and accessibility.
• Tree survey, arboricultural impact assessment and tree protection plan.
• Preliminary ecological appraisal, short form, with a biodiversity position statement.
• Drainage details including the infiltration test result.
• Visibility and vehicle tracking drawings.

Nine documents for one house, and the tree work was the expensive part. Compare the pattern with the care home walkthrough, where scale rather than constraint drove the list.

Conditions protecting the host dwelling

Permission came with obscure glazing to two windows, retention of the host dwelling's parking, the tree protection measures, boundary treatment details, removal of permitted development rights for extensions and outbuildings on the new plot, and a construction method statement covering the shared access.

The permitted development restriction is the one self-builders resent and the one most likely to be imposed on a tight backland plot. It is also the condition that made the scheme acceptable, because the officer could grant knowing the plot would not fill in later.

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. Enter your postcode on PlanScope to see which reports a garden plot needs.