Building a new house in your garden, sometimes called a garden infill development or self-build plot, is something many homeowners consider. The appeal is obvious: if you have a large enough garden, you could sell the new house, give it to a family member, generate rental income, or use the proceeds to fund other plans. Whether it is achievable depends on a range of factors that vary from one property to the next.

This guide explains the planning framework that governs residential garden development, the key factors that determine whether planning permission is likely to be granted, and the practical steps involved in taking the idea forward.

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You Will Need Planning Permission

Building a separate dwelling in your garden is a new residential development and always requires planning permission. There are no permitted development rights that allow you to build a new house in a garden without going through the planning process. Even a very small house or a self-contained unit for a family member requires a formal planning application.

This does not mean the application will be refused. Many garden infill applications are successful, particularly in areas where housing demand is high and the plot is genuinely suitable. But the starting point is that permission is required and is not automatic.

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What Planners Will Consider

When a planning application is made to build a new dwelling in a garden, the local planning authority assesses it against national planning policy, the local development plan, and the specific characteristics of the site. The main considerations are as follows.

Whether the site is in a sustainable location

National planning policy favours residential development in sustainable locations with good access to services, public transport, and employment. A large garden in a well-connected urban or suburban area is more likely to be considered suitable for a new dwelling than one in a rural location with poor access.

The impact on the character of the area

Planners will assess whether a new dwelling in the garden would harm the character and appearance of the surrounding area. In streets where houses are set well back from the road with generous front and rear gardens, a new dwelling inserted between or behind existing houses may be considered out of keeping. In more densely developed areas where infill is common, the same proposal may be entirely acceptable.

The impact on neighbouring amenity

A new dwelling in a garden can affect the light, privacy, and outlook enjoyed by neighbouring properties. Planners will consider whether windows would overlook neighbours, whether the building would overshadow adjacent gardens or rooms, and whether the additional activity from a new household would cause unacceptable disturbance.

Access and parking

The new dwelling will need its own access to the public highway, either shared with the existing house or separate. There must be adequate space for parking within the curtilage. The impact of the additional vehicle movements on highway safety may be considered, particularly on narrow or busy roads.

Garden land policy

Some local planning authorities have specific policies about developing garden land, sometimes called garden grabbing. These policies may set out standards for minimum plot sizes, minimum distances between dwellings, or the proportion of garden that can be built on. Check your local planning authority's development plan for any specific garden land policies that apply in your area.

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Splitting the Title

If you want to sell the new dwelling rather than keep it as part of your existing property, you will need to split the title of your land at HM Land Registry. The part of the garden on which the new house is built is separated into a new title, which can then be transferred to a buyer independently of your existing home.

Title splitting is a legal process handled by a solicitor or conveyancer. It requires a plan clearly showing the boundary between the existing property and the new plot. If your existing property has a mortgage, you will need your lender's consent to sell part of the land, as the property secures the mortgage and selling part of it reduces the security available to the lender.

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Infrastructure and Utilities

A new dwelling needs its own connections to the mains water supply, drainage, gas, and electricity networks. In some cases these connections can be made from the existing house's services; in others, new connections from the street will be needed. The cost and complexity of these connections varies significantly by location and should be investigated early in the planning process, as they can materially affect the viability of the development.

Drainage is particularly important. If the site cannot connect to the public sewer, alternative drainage solutions such as a treatment plant or septic tank may be required, subject to their own regulatory requirements.

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Community Infrastructure Levy and Section 106

New residential development may be subject to a Community Infrastructure Levy charge or a Section 106 planning obligation, requiring financial contributions toward local infrastructure such as schools, roads, and open space. The amounts vary by local authority and can be significant for new dwellings. Check whether a levy applies in your local authority area before proceeding.

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Summary

Building a new house in your garden is achievable in many circumstances but requires planning permission, which is assessed against local and national planning policies. The key factors are whether the location is sustainable, whether the development fits the character of the area, whether neighbouring amenity is protected, and whether access and parking are adequate.

Pre-application consultation, an experienced planning consultant or architect, and early investigation of infrastructure requirements are the practical foundations of a successful garden development project. Where the plot is well-suited and the planning case is strong, garden infill development can be a financially rewarding and legally sound project.