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  1. Blog
  2. When does a conservatory become an extension?
Advice about properties
08 March 2022

When does a conservatory become an extension?

Sam Edwards
Senior Writer & Researcher
When does a conservatory become an extension?

Table of contents

  1. 1. At what point does a conservatory become an extension?
  2. 2. Conservatories vs extensions - what's the difference?
  3. 3. Conservatories
  4. 4. House extensions
  5. 5. How much is a conservatory extension?
  6. 6. How much is a house extension?
  7. 7. What's better - a conservatory or an extension?
  8. 8. Can you turn a conservatory into an extension?

Conservatories and extensions are some of the most popular home improvements among homeowners. Though we often use the words interchangeably, conservatories and extensions are actually different builds with very distinctive features. With this being the case, when does a conservatory become an extension, and is it possible to turn your conservatory into an extension?

At what point does a conservatory become an extension?

Conservatories become extensions when they exceed their permitted development rights and then require planning permission. But what are a conservatory's permitted development rights?

Permitted development means where you're allowed to build without planning permission. In the case of a conservatory, you don't need planning permission as long as:

  • Your conservatory does not extend beyond the side of your house.
  • Your conservatory doesn't exceed 4 metres in height.
  • The space your conservatory occupies is smaller than half of the area around the original house.
  • Your conservatory isn't taller than the highest part of your existing property's roof.
  • Where the conservatory comes within 2 metres of the boundary (the edge of the area of enclosed space surrounding the house), the height at the eaves is below 3 metres.
  • If your conservatory is on the front of the house or the side of the house, it should not be closer to any public right of way (footpaths) than the original house.
  • You don't add any extensions or accessories that could potentially infringe on your neighbour's privacy.
  • If you have a detached house and your conservatory is a rear extension, it can't extend beyond the rear wall of your house by more than 4 metres. If your house isn't detached, this should be less than 3 metres.

Conservatories vs extensions - what's the difference?

Aside from planning permission, there's a number of functional and aesthetic attributes that distinguish conservatories and extensions from one another. Conservatories are usually built with more than 75% of their structure consisting of glass unlike extensions. Extensions also tend to feature solid (tiled) roofs with minimal glass but may feature a skylight, unlike conservatories which feature glass roofs.


Conservatories were traditionally used as garden rooms due to their glass roof and walls. The resulting natural light was used to rear plants and green life. Today, these glass extensions are an increasingly popular, cost-effective investment in extra living space for homeowners. Typically, they are glass-built structures attached to the rear of the home. They usually have glass roofs but you can get a tiled roof without having to apply for permission.

Please note: While you can replace your conservatory roof with a solid or flat roof, you may need to upgrade the rest of the build to compensate. Solid roofs are heavy and if the walls aren't strong enough, you may need to add new ones.


Conservatories don't require planning permission as long as they’re built within permitted development rights - however, they do require Building Regulations approval from a LABC certified (Local Authority Building Control) surveyor.

Cheaper than extensions (Typically)

Conservatories tend to cost much less than extensions because the building process isn’t as long, the materials are cheaper, and less space is required.

Low energy efficiency

Conservatories have a low energy efficiency because they’re not built with high performance glass or insulated walls. Conservatory roofs usually lack insulation too.

Classified as uninhabitable living spaces

As they lack the fortitude and warmth of a house extension, conservatories are classified as 'uninhabitable living spaces'.

House extensions

Unlike conservatories, house extensions don't have one single traditional use. Thanks to their glazed walls and attractive design, a new extension is a significant investment in extra space.

More flexibility

They can be constructed in different places for different purposes. They can incorporate a new kitchen, bedroom, bathroom, lounge, or dining room design for use all-year round.


Extensions must have planning permission and Building Control certification, making them a significant home improvement.

More bespoke

Homeowners usually hire architects to design extensions because architectural designs are required in the planning application process.


House extensions are built with specially designed pillars that provide greater structural integrity than conservatories.


Extension costs far exceed the costs of conservatories.

Energy efficient

Double glazing provides high thermal insulation, saving you money on energy bills.

Classified as living spaces (When designed correctly)

Extensions tend to be more visually pleasing both inside and out, adding palpable market value to your property.

How much is a conservatory extension?

Conservatories come in all shapes and sizes, but how much can the average person expect to pay for one? The average conservatory costs between £5000 to £10,000, but this can be much higher depending on the type of materials you use and the size of your conservatory. The larger your conservatory, the more likely it is to be classed as a ‘house extension' and require planning permission.

How much is a house extension?

House extensions tend to be much more expensive than conservatories because they're built with sturdier, thermally insulated walls, and have greater foundations. As such, smaller rear house extensions cost around £15,000 to £20,000 to build, whereas medium size extensions cost somewhere around £40,000.

What's better - a conservatory or an extension?

Ultimately, it's down to your preference and budget. But for the most part, we think house extensions are a much better use of money, time, and space.

  1. Firstly, conservatories are not as thermally efficient as extensions, which means they get much colder in the winter. You can use a heater, but this isn't really the same as a warm, thermally insulated room in your own house.
  2. Secondly, with an extension, you have a lot more possibilities as to what you can build with it. With a conservatory however, your options are limited by its size, scope and materials.

While extensions definitely cost a lot more than conservatories, we think it's worth saving for a worthwhile investment rather than something that could prove to be lacklustre years down the line.

Before making any plans to build a conservatory or extension, make sure your home isn't located in a conservation area. If your home falls within a conservation area, you may be prohibited from making specific changes to your property. Mitigate any problems by enquiring first with your local council.

Can you turn a conservatory into an extension?

Yes, you can turn a conservatory into a house extension, but this isn't a walk in the park. Extensions require planning permission and Building Regulations, which can result in a completely new structure in order to satisfy their requirements.

How much does it cost to extend a conservatory?

A builder's estimate for a conservatory conversion into a single storey extension would be around £15,000 to £20,000. However, this is only a ballpark figure. The existing conservatory may work to reduce your costs.

What's the benefit of turning a conservatory into an extension?

Technically, a conservatory is classed as a 'uninhabitable living space'. As a result, it won't add loads of value to your property. Thanks to their thermal performance and superior design, standard extensions _are _classed as habitable living spaces. As a result, an extension will add palpable value to your property.

What's more, you can turn an extension into an extra bedroom or kitchen. Or better still, add an additional floor and create a two storey extension.

Can you use conservatory foundations for an extension?

Yes, it is possible to use your conservatory's base for a house extension. However, the foundations may have to be upgraded if they are not wide or deep enough.

Things to consider if you're extending your conservatory

If you're considering turning your conservatory into an extension, we've got some tips to help you save significantly on future repairs.

  1. Make sure your foundations and roof are examined and signed off by the LABC. Foundation issues will affect the overall quality of your new room and may cause problems further down the line.
  2. Try and get LABC approval and Building Control certification on the whole job rather than just the roof. An incorrectly refurbished or extended conservatory poses a big risk to health and safety.

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