Replacing a Conservatory With an Extension: A Builder's Guide to Getting It Right
Updated: Oct 9
Your conservatory is too hot in summer, too cold in winter and loud every time it rains. You have stopped using it, and you are wondering whether to knock it down and build a proper room in its place. For a lot of homeowners that is the right call, but planning rules, Building Regulations and the state of the old base all affect what the job involves. Here is how it works, based on the conservatory replacements we carry out across Berkshire and Oxfordshire.
What does replacing a conservatory with an extension involve?
Replacing a conservatory with an extension means removing the old structure completely and building a new, fully insulated room in its place, usually on new or upgraded foundations. Unlike a conservatory, the new room is built to the same standard as the rest of the house, so it stays comfortable all year.
When we replace a conservatory with a timber frame extension, the job usually runs in this order:
Survey. We look at the existing base, the house wall it joins and how much space the plot allows.
Design and approvals. We agree the layout, then check planning and arrange Building Regulations approval.
Removal. The glazing, frames, roof and dwarf walls come down and are cleared from site.
Foundations. The old base is either upgraded or replaced so it can carry a solid structure.
Structure. The insulated frame goes up, followed by the roof, windows and doors.
Opening up. If you want the room open to the house, the wall between them is opened and supported.
Fit-out. Electrics, heating, plastering, flooring and decoration finish the room.
Our conservatory removal and the new build are handled by the same team, so there is no gap between one trade leaving and the next arriving.
When replacing your conservatory with an extension makes sense
Replacement is usually the better route when the conservatory itself is the problem. That tends to mean one or more of these:
The frames or base are old, damaged or moving
The room is too small or the wrong shape for what you want
You want a kitchen, open-plan living area or anything that needs solid walls
You want the room fully open to the house, not shut off behind patio doors
In those cases, spending money upgrading the old structure only gets you part of the way. A new extension gives you a room designed for how you want to use it.
When upgrading the conservatory is enough
If the base and frames are sound and the footprint already works, you may not need to start again. The biggest problem with most conservatories is the roof. Swapping it for an insulated solid roof through a conservatory roof replacement cuts glare and rain noise and makes the room far more comfortable through the year. We will tell you honestly which option suits your conservatory after the survey.
Replacing a conservatory with an extension: planning permission
Many conservatory replacements do not need a planning application. Single-storey extensions can often be built under permitted development rights, as long as they stay within set limits. The new extension has to meet those limits in its own right. The fact that a conservatory stood in the same spot does not by itself give you permission for a solid extension of the same size.
The main permitted development limits
For a single-storey rear extension on a house in England, the Planning Portal sets out the permitted development rules. The key ones are:
Depth: no more than 3 metres beyond the rear wall of the original house, or 4 metres for a detached house. This can rise to 6 and 8 metres through a prior approval application, except on designated land.
Height: no more than 4 metres, and no more than 3 metres at the eaves within 2 metres of a boundary.
Coverage: extensions and other buildings cannot cover more than half the land around the original house.
Materials: the outside must be of a similar appearance to the existing house.
The "original house" means the house as first built, or as it stood on 1 July 1948. Any earlier extensions count towards the limits, so it is worth knowing your home's history before you plan the size.
When you will need to apply
You will usually need to apply for householder planning permission if the extension goes beyond those limits, or if your property does not have permitted development rights. That includes flats and maisonettes, and homes where a planning condition or an Article 4 direction has removed those rights.
Homes in conservation areas, National Parks and other designated land have tighter rules. For example, exterior cladding is not allowed under permitted development on designated land. If you are unsure, your local council can confirm what applies.
Building Regulations: the bigger change
This is the part many homeowners do not expect. According to the Planning Portal, conservatories are normally exempt from Building Regulations when they are single storey, at ground level, under 30 square metres, separated from the house by external-quality walls, doors or windows, and have their own heating controls.
An extension does not get that exemption. Building Regulations will generally apply, covering structure, insulation, ventilation and fire safety. Any new structural opening between the house and the room also needs approval. We arrange this as part of every replacement we build.
How much does it cost to replace a conservatory with an extension?
The cost depends far more on what you are building than on what you are taking down. Removing the old conservatory is usually a small part of the bill. The new extension itself, its size, finish and specification, makes up most of it.
These are the things that move the price most:
Size and shape. A larger footprint or a more complex roof adds materials and labour.
The existing base. Many conservatory bases were not built to carry solid walls and a tiled roof. We check the foundations first, because upgrading or replacing them changes the cost.
Opening up to the house. Removing part of the back wall needs structural support and approval.
Roof and glazing. Roof lanterns, bi-fold doors and large windows add cost.
Fit-out. A kitchen or bathroom costs far more to finish than a living room or dining space.
Building in timber frame helps keep the cost down, mainly because the structure goes up in days rather than weeks. For a breakdown of typical figures, see our guide to how much a timber frame extension costs. Whatever you build, get an itemised quote that includes the removal, foundations and Building Regulations work, so you are comparing complete jobs.
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