House extensions: The Ultimate GuideLearn More
This morning I sent out a group email to all our architects, which read, ‘What question are you most often asked from homeowners who are looking to extend?’ In a short time, my inbox was flooded with replies stating, ‘Do I need planning permission for a conservatory?’
Wanting to see what information was out there, I typed the question into Google. Over 2 million pages came back covering the same topic! I found it worrying just how much conflicting/incorrect information existed.
This is because the answer is complex and depends on several factors. To simplify, I give below a detailed assessment of the relevant policies and guidance notes.
1. What is a Conservatory?
Most people tend to define a conservatory as a single storey structure added to an existing house made from glass, supported by either UPVC or wood. This is slightly different to an extension, which tends to be a brick-built structure with a solid roof.
Although conservatories and extensions might look different, the planning system assesses them in the same way. Local planning policies and permitted development guidance (discussed in more detail below) don’t make any distinction between the two. When planning policy or guidance documents found online refer to ‘extensions’ they also refer to conservatories.
2. How do I know if I need planning permission for a conservatory?
When it comes to extensions there are two routes to go down: either ‘Permitted Development’ or ‘Planning Permission’.
The first step is to make a note of your design ideas and then check them against the permitted development guidance to see if they fit.
The legislation covering what is/isn’t considered to be permitted development can be found here.
I find the above document quite difficult to understand, so I recommend looking at the Planning Portal. It’s a government website and includes loads of useful guidance on permitted development.
To help understand this, I have included the relevant policies in bold text below, along with some helpful bullet points.
2.1. For all extensions
Only half of the area of land around the “original house” can be covered by an extension or other buildings.
- The ‘area of land’ not only covers your rear garden but also includes your front garden and any side passageways.
- The footprint of any existing extensions or outbuildings would be included as part of that 50% limit.
Extensions cannot be higher than the highest part of the existing roof, or higher at the eaves than the existing eaves.
- The highest part of the existing roof would be the ridge.
- The eaves refer to the area at a similar height to your gutters overhanging your roof.
Where the extension comes within two metres of the boundary* the height at the eaves cannot exceed three metres.
- The eaves height is measured from ground level at the base of the outside wall, up to where the wall meets the upper surface of the roof slope (see diagram below).
The building of the extension must not be forward of the ‘principal elevation’ or, where it fronts a highway, the ‘side elevation’.
- The principal elevation refers to the space in front of your house
- ‘Fronting a highway’ refers to houses located on the corner of two roads
The work cannot include any of the following: verandas, balconies* or raised platforms, a microwave antenna (e.g. TV aerial or satellite dish), a chimney, flue or soil and vent pipe, any alteration to the roof of the existing house.
- Any of the above works would require you to apply for planning permission.
On Article 2(3) designated land* the work cannot include cladding of the exterior.
- Article 2(3) land refers to houses within conservation areas.
- If your house is located within a conservation area you would require planning permission to clad the exterior of your house.
The materials used in any exterior work must be of a similar appearance to those on the exterior of the existing house.
- If your existing house is built of bricks any proposed extension would also be required to be built of bricks.
- However, if your existing house is rendered, the new extension would also need to be rendered to match.
2.2. For single-storey rear extensions
Single-storey rear extensions cannot extend beyond the rear wall of the original house* by more than four metres if a detached house; or more than three metres for any other house.
- If you own either a terraced or semi-detached house the maximum extension depth would be 3m.
- If your rear extension extends beyond the sidewall, it cannot be more than half the width of the original house.
Where not on Article 2(3) designated land* or a Site of Special Scientific Interest; and subject to ‘prior approval’, the limit for single-storey rear extensions is increased to eight metres if a detached house; or six metres for any other house.
- The government have extended the permitted development depths of single-storey rear extensions.
- This process involves the local planning authority writing to all the neighbours who join your property. Planning approval goes ahead if objections are not given. However, if any of your neighbours object, then your local planning authority will make a decision based on the impact on their living conditions, such as loss of light or view.
Single-storey rear extensions cannot exceed four metres in height.
- Measure the height from the ground level of the outside wall to the extension’s highest point.
3. Do I need planning permission for a conservatory if it does not meet the Permitted Development Guidance?
If the proposed plan for your new extensions falls outside the above guidelines, you would need to apply for planning permission.
That is not to say your resulting extensions would become smaller. In some cases, taking the planning permission route can help and give your more space when compared to permitted development.
How big can a conservatory be without planning permission?
When it comes to planning permission, each local authority will have slightly different planning policies. Many have a ‘Residential Design Guidance’ document, showing homeowners what is acceptable. This document should appear by carrying out a Google search of your local authority’s planning policy web page.
As a general rule of thumb when it comes to single-storey rear conservatories, the following depths are acceptable:
Terrace: 3m deep
Semi-detached: 3.5m deep
Detached: 4m deep
The above is just a guide, and you should check before applying.
Permitted development guidance and local planning policies can be quite long and difficult to interpret.
When considering whether your conservatory would require planning permission, I would suggest calling a local architect and discussing your proposed ideas with them. They should have a very good understanding of the policies in your area and will be able to advise you on which route to take.
At Adara, many of our team previously worked as local authority planning officers so we have a very good understanding of the entire process. If you have any questions or need advice, please feel free to call our team at any time for a free consultation.
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