Does Your Extension Need Planning Permission?

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You have to check whether your extension needs a planning consent since if planning consent is required and you start building without having the planning consent, you could be served with a legal notice ordering your home extension to be demolished by the Local Authorities.

The planning permission need is determined by factors such as the size of your build, the Permitted Development rights that apply to your property, and whether you live in a conservation area.

Since the application process might be very complicated, Studio 20 Architects prepared a guide where you can find information regarding extensions. Studio 20 Architects assists your house’s extension plans and assists you with if you need conservatory planning permission (a.k.a. loft conversion planning permission).

In this guide, Studio 20 Architects’ professionals summarized some of the rules about the projects which do need and do not need planning permission.

However, only looking at this guide to understand the regulations concerning extensions and planning application and permission might not be enough, you have to check with professionals such as local planning authority or your architect before you begin with your extension project.

Permitted development rights

The planning law allows some small extensions to be built without having to submit a planning application to your local council is called ‘permitted development rights’. The examples that are subject to permitted development rights are such as some conservatories and loft conversions.

However, the rules regarding permitted development rights are complex and confusing, therefore, a piece of professional advice might be helpful and facilitating. You can find our more information here about the permitted development rights.

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Single-storey extension

If you are planning a do single-storey extension, you might not need planning permission to extend a semi-detached or terraced house by eight metres to the rear. There are also height restrictions in single-storey extension projects.

Single-storey side extensions are allowed if the extension is more than four metres in height. Moreover, a side extension cannot be more than half the width of the original house.

Two-storey extension

In Two-storey extensions, the extension is only considered to be permitted developments if it does not extend beyond the rear wall of the house by more than four metres.

Moreover, the extension is considered to be permitted development if it is no closer than seven metres to the rear boundary. Another condition for your extension to be permitted is the fact that it needs to include upper, side-facing windows that have obscure glazing.

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Loft conversions

If your loft conversion is within specific limits, planning permission is not normally required. You can convert your loft to add up to 40 cubic metres of extra living space in a terraced house or semi or 50 cubic metres in a detached house.

Flush roof lights or those which do not project more than 150 millimetres are permitted, but you will need planning permission to add a dormer or roof light on any elevation which faces the road.

Moreover, planning permission is needed for a balcony, and planning permission is needed if the loft conversion extends beyond the slope of the current roof-line.

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Listed buildings & conservation areas & national parks

There are specific areas that are subject to special planning permission kinds. For example, listed buildings need listed building consent for internal and external changes.

If you live in a conservation area or area of outstanding beauty or national park, you do not have standard permitted development rights, to build an extension your rights are limited and you will need special consents.

Therefore, if you live in such special areas, contacting the local planning authority or getting advice from your architect is best before starting any extension project.

Garage conversion

Planning permission is not usually required for converting a garage into liveable rooms if you are doing the work inside and do not alter the structure of it or extend it.

However, checking with your local authority is still important since in some areas since permitted development rights have been removed from properties for garage conversions.

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Basement conversions

Converting an existing cellar or basement into living space does not usually need planning permission just like converting garages unless a light well is added which alters the external appearance or it will be turned into a separate flat.

However, digging under the building to create a new basement is likely to need planning permission.


Full Planning Applications include:

Special reports concerning your application such as Heritage Statement, Flood Risk Assessment, Arboricultural Report

Studio 20 Architects will advise the necessary documents if required for your planning application

All existing drawings of the property such as floor plans, elevations, sections

During the planning application journey, Studio 20 Architects will provide every drawing that is necessary for the Local Council to approve the planning application.

Application forms, Notification letters, CIL Questions

All proposed drawings such as floor plans, elevations, sections, site plans

During the planning application journey, Studio20 Architects will provide every drawing that is necessary for the Local Council to approve the planning application.

If required, a detailed Design and Access Statement

Site plan and block plan, Ordnance Survey Map