A conservatory that is too hot in July, too cold in January and shut behind its doors for half the year is floor area you already own and cannot use. This page is for homeowners who want a proper room in its place. It covers the three ways to do it, the planning position, what building control will ask for, whether the old base can stay, what it costs and how long it takes. The Extension Company designs these across London, and North London projects are designed, managed and built by Pine Grove Design & Build's own team.
Why people replace a conservatory
- Too hot and too cold. Glazed walls and a glazed or polycarbonate roof take in heat quickly in sun and lose it quickly in winter. The room works in spring and autumn and needs constant heating or shading the rest of the year.
- Leaks. Roof panels, seals and the flashing where the roof meets the house wall wear out, and an ageing conservatory roof is usually where the water gets in.
- It was never part of the house. A conservatory stays exempt from building regulations only while it is separated from the house by external-quality doors and heated on its own controls. It is built to be a room you walk out to, not one the kitchen opens into.
- Someone has already knocked through. Take out the doors and the exemption ends: the structure is then judged as an extension, and a mostly glazed room rarely meets that standard. It tends to surface when a buyer's solicitor asks for the completion certificate.
Three ways to fix it: a new roof, an orangery or an extension
A solid roof on the existing frame
The glazed or polycarbonate roof comes off and an insulated solid roof goes onto the existing frames. It is the least disruptive option, and it deals with the roof and nothing else: the walls are still glazed frames, and the floor and base are what they were.
Two things to know before choosing it. First, it needs building regulations approval. Once the roof is no longer glazed the structure stops counting as an exempt conservatory, the new roof has to meet the regulations, and building control will want to know that the frames and the foundations can carry it, often by asking for a trial hole. Second, the doors to the house generally have to stay. Remove them and the whole structure is treated as an extension, glazed walls included.
It suits a sound conservatory that will carry on as a separate room. It does not give you an open-plan kitchen.
Rebuild as an orangery
The conservatory comes down and a room with brick piers, an insulated flat roof and a glazed lantern goes up in its place. It keeps the daylight that made a conservatory appealing and adds the solid structure that makes the room usable in February. It is designed, inspected and certified as an extension, so it can open straight into the house. Our orangeries page covers the design, and the orangery cost guide has the figures.
Rebuild as a single-storey extension
Solid walls, an insulated roof with rooflights where the plan needs them, and wide glazed doors to the garden. It gives the most usable wall and the most freedom over layout, and it is the usual answer when the real aim is a bigger kitchen. See single-storey and rear extensions for the shapes that suit each type of house, and kitchen extensions if the kitchen is moving into the new space.
| Solid roof on the existing frame | Orangery | Single-storey extension | |
|---|---|---|---|
| What is kept | Frames, floor and base | Normally nothing | Normally nothing |
| Building regulations | Approval for the new roof, with the frames and base checked for the load | Full approval, as an extension | Full approval, as an extension |
| Open to the house | No, the doors stay | Yes | Yes |
| Year-round comfort | Better than before, limited by the glazed walls | Close to normal room comfort | Full, built to current standards |
| 2026 build cost | Depends on the roof system; we do not publish a figure | £60,000 to £95,000 for about 20 to 30m² | £2,800 to £4,200 per m² |
Most people come to us for an orangery or an extension, and new rooms are the work we are set up for. We can fit a replacement roof, or rebuild a conservatory, where that is the right answer. If yours is sound and the only complaint is temperature, a new roof may be all it needs, and we will say so at the visit.
Do you need planning permission to replace a conservatory with an extension?
Often not, but the old conservatory gives you no head start. Planning has no like-for-like right to rebuild: whatever permission or permitted development right covered the conservatory does not pass to the room that replaces it. The replacement is a new single-storey extension, judged against the householder permitted development rules in the General Permitted Development Order 2015 (Schedule 2, Part 1, Class A). On a house that still has its permitted development rights, it needs no planning application if it stays within these limits:
- Depth: no more than 3m beyond the rear wall of the original house on a terraced or semi-detached house, or 4m on a detached house.
- Height: 4m at most, and no higher than the existing house at eaves or ridge.
- Eaves near a boundary: no more than 3m to the eaves where the extension comes within 2m of a boundary.
- Position: nothing beyond the front of the house, or beyond a side wall that faces a road.
- Side extensions: single storey, no more than 4m high and no wider than half the original house.
- Plot coverage: together with other extensions and outbuildings, no more than half the land around the original house.
- Materials: similar in appearance to the outside of the existing house.
The limits are measured from the original house
Original house means the house as first built, or as it stood on 1 July 1948. Unless your conservatory was already there in 1948, it is not part of the original house, and three things follow.
- Depth is measured from the rear wall of the original house, which is usually the wall the conservatory stands against, and not from the conservatory's outer edge. A 3m conservatory on a semi can be replaced by a 3m extension under permitted development. It cannot be replaced by one that reaches 3m beyond where the conservatory ended.
- If the conservatory is deeper than 3m (4m on a detached house), or sits on the back of an earlier extension, a replacement of the same size can be outside the basic limit even though you are building no further out than before. It then needs prior approval or a householder application.
- If part of an older extension stays and the new room joins it, the two are measured together as one enlargement.
The materials rule catches replacements
Permitted development requires the outside of an extension to be in materials similar in appearance to the existing house. The rule makes one exception, for a conservatory, and that exception goes when the conservatory does. On a brick house that means brick of a similar appearance to the existing walls. A replacement in a visibly different material needs a planning application.
When prior approval or a planning application is needed
- Deeper than the basic limit: up to 6m on a terrace or semi and 8m on a detached house is possible through prior approval under the larger home extension scheme. You notify the council (£249), the neighbours are consulted, and the council has 42 days to decide.
- Beyond that, or outside the other limits: a householder planning application (£548), with an eight-week statutory decision period. That covers a side or wrap-around replacement wider than half the original house, and materials that do not match.
- Flats and maisonettes: no permitted development rights for extensions, so any replacement needs an application.
- Rights removed by condition: if the conservatory was approved by a planning application, read the decision notice. A condition on it, or on the permission for the house itself, can take permitted development rights away.
- Conservation areas: a single-storey rear replacement inside the 3m or 4m limit can still be permitted development, but side extensions, cladding and the 6m or 8m prior approval route are not available. An Article 4 direction can remove the extension right altogether. Our conservation area extensions guide shows how those rules change a design.
- Listed houses: listed building consent is needed.
| Route | Fee | What to expect |
|---|---|---|
| Lawful development certificate (permitted development) | £274 | Optional. The council confirms in writing that the replacement is lawful |
| Prior approval, larger home extension | £249 | Neighbours are consulted; the council has 42 days to decide |
| Householder planning application | £548 | Eight-week statutory decision period from validation |
A lawful development certificate as proof
Inside the limits there is no application to make, but a lawful development certificate for proposed works (£274) is worth having on a replacement more than on most jobs. Whatever paperwork exists for the old conservatory does not describe the new room, and the certificate is the council's written confirmation that the extension is lawful. Our lawful development certificate guide explains how to apply, and every fee is in the planning fees guide.
Building regulations: the exemption ends with the conservatory
A conservatory is exempt from building regulations only while it meets five conditions: it is built at ground level, has a floor area under 30m², is separated from the house by external-quality walls, doors or windows, has independent heating controls, and has safety glazing where the regulations require it. Our conservatory planning permission guide sets those out in full.
An extension or an orangery has no such exemption. Building control approves the design, inspects the work and issues a completion certificate, and on a conservatory replacement these are the points that matter:
- Foundations and structure. Designed for masonry walls and an insulated roof, and checked by building control as the job goes up.
- Insulation. New walls and floors have to reach a U-value of 0.18 W/m²K and a new roof 0.15 (Approved Document L, Table 4.2). A conservatory never had to.
- The glazing limit. Windows, doors and rooflights in an extension are limited to 25% of its floor area, plus the area of any openings the extension covers up. More glass is allowed if it is made up for elsewhere, shown by an area-weighted U-value calculation or an energy calculation for the whole house. That is how an orangery with a lantern passes, and why a room that is mostly glass struggles to.
- The opening into the house. Taking out the wall between the house and the new room, or widening the old doorway, is a new structural opening. It needs approval in its own right and a beam designed by a structural engineer, and if the steel bears into a wall shared with a neighbour, a party wall notice two months ahead.
- Drainage, ventilation and electrics. All designed and signed off. If a public sewer runs under the footprint or within 3m of it, the water company's build-over agreement is needed before work starts.
The completion certificate is the document a buyer's solicitor will ask for when you sell. Our guide to building regulations for extensions goes through the approval process.
Can the existing conservatory foundations be reused?
Usually not, and never on trust. There are three reasons.
- Nobody inspected them. An exempt conservatory is built without building control seeing the base, so there is normally no record of how deep or how wide it is.
- They were sized for a lighter building. Glazed frames on a low wall weigh far less than masonry walls carrying an insulated roof.
- Clay. Much of North London sits on clay. Approved Document A sets a minimum foundation depth of 0.75m to 1.0m on shrinkable clay, depending on how much the clay moves, and more where there are trees nearby. A conservatory base that does not reach that depth is unlikely to be accepted for an extension.
A trial hole settles it. Dug beside the base, it shows how deep and how wide the foundation is and what it sits on. If that meets the standard for the new load, building control can accept it and part of the base stays. If it does not, the base is broken out and new foundations are dug, and that is the outcome to budget for. The floor is a separate question: an extension floor has to meet the current insulation standard, and unless the old slab can be shown to, it comes up too.
What it costs to replace a conservatory in 2026
Price the job as the extension or orangery it is. These are the 2026 build ranges published across this site, with the extension rows at North London rates, excluding VAT, professional fees and any kitchen fit-out. Pick the row nearest the footprint you want.
| Replacement | Size | Build cost, 2026 |
|---|---|---|
| Single-storey extension | 3m × 3m, 9m² | £25,000 – £38,000 |
| Single-storey extension | 3m × 4m, 12m² | £34,000 – £50,000 |
| Single-storey extension | 3m × 5m, 15m² | £42,000 – £63,000 |
| Single-storey extension | 4m × 5m, 20m² | £56,000 – £84,000 |
| Classic orangery | About 20 to 30m² | £60,000 – £95,000 |
| Large orangery | About 30 to 45m² | £85,000 – £130,000 |
The extension rows are £2,800 to £4,200 per m². Most extension work carries VAT at 20%, and a new kitchen, if the room is getting one, runs £8,000 to £30,000 depending on spec. The ranges are for the new build: taking down the old conservatory, breaking out its base and carting both away is a separate cost, so allow for it on top.
Our North London extension cost guide lists everything a build price leaves out, and the orangery cost guide does the same for orangeries. Nothing on this page is a quote. After a free design visit you get a fixed, itemised price, so the number you sign is the number you pay.
How long it takes
Design and drawings take two to three weeks from the survey. A permitted development scheme needs no decision from the council, though the certificate is worth having; prior approval gives the council 42 days, and a householder application has an eight-week decision period. On site, a typical single-storey rear extension takes about three to four months, and an orangery ten to fourteen weeks depending on span and finish. Party wall notices, where they apply, go out one to two months before work starts; our party wall guide sets out which notice applies. The conservatory stays in use until the build begins, and taking it down is the first job on site.
How we run a conservatory replacement
The Extension Company is the extensions studio of Pine Grove Design & Build Ltd. We design across London, and projects in North London are designed, managed and built by Pine Grove's own team.
- Free design visit. We measure the conservatory and the house behind it, work out which wall is original, check the boundaries and the drains, and tell you which planning route applies.
- Design and drawings. The layout, the opening into the house, the steels and the glazing are drawn before anything is priced. Where keeping the old base is a real possibility, a trial hole answers it at this stage.
- Consents. Lawful development certificate, prior approval or householder application, building regulations, and party wall notices served alongside so the clocks run together.
- Fixed, itemised quote. Every element priced, demolition included, before you commit to anything.
- Build. In North London, Pine Grove's own team builds it, from taking down the conservatory to handover.
Ready to swap the conservatory for a room you can use all year? Compare the two replacements on our orangeries and single-storey extensions pages, get a rough figure for your size from the Extension Builder, or book a free design visit. Call 020 3051 9430 to speak to the team.