In London in 2026, replacing a conservatory with a solid extension costs roughly £2,800 to £5,500 per m² for the build, or about £60,000 to £150,000 all in for a small-to-medium rear extension. Removing the old conservatory adds £800 to £2,500. Like-for-like replacements often need no planning permission, but the new space must meet full Building Regulations, and a quality extension can add around 5 to 10% to a home’s value.
Many homeowners end up with a conservatory they no longer use as intended. It becomes the place the bikes live, or where the washing dries, because it is too hot in summer and too cold to sit in through winter. Replacing that conservatory with a properly built extension is one of the most popular ways London homeowners reclaim the space, and it is usually a better long-term investment than repairing or reglazing an ageing conservatory.
This guide covers what the work costs in 2026, whether you need planning permission, the building regulations that apply, the value it can add, and what a real conservatory-to-extension project looks like before and after.
How much does it cost to replace a conservatory with an extension?
For a London project in 2026, budget £2,800 to £5,500 per square metre for the new extension build, depending on specification. Removing the old conservatory is a separate, smaller cost of £800 to £2,500. Most replacement projects land in these brackets:
| Item | Indicative 2026 cost (London) |
|---|---|
| Removing the existing conservatory | £800 to £2,500 |
| New solid extension, build only | £2,800 to £5,500 per m² |
| Small replacement (15 to 20 m²), all in | £60,000 to £110,000 |
| Medium replacement (20 to 30 m²), all in | £80,000 to £150,000 |
| Professional fees, planning and surveys | add 10 to 15% on top |
London costs sit above the UK average because of labour demand, tighter site access and stricter planning. The figures above are indicative, and the real price depends far more on design and material choices than on floor area alone. For a fuller breakdown of rates by extension type, see our guide to extension costs per square metre in London.
The teardown itself is the cheap part. A lightweight uPVC or lean-to conservatory strips out quickly because the frame is bolted on rather than bonded into the wall. The cost sits in what comes next: foundations, structure and a build that meets current energy standards.
Can the existing foundations be reused?
Sometimes, but rarely in full. Conservatory footings are usually shallow and were never designed to carry a solid, insulated structure with a tiled or warm flat roof. If a structural engineer confirms the existing base and dwarf wall are sound, you may be able to build up from the plinth using insulated studwork faced with brick, which keeps costs down. If they are not suitable, a full rebuild of the base is needed, and underpinning or new trench-fill foundations can add several thousand pounds. This is assessed with trial pits before any work is signed off.
Is it cheaper to convert the conservatory or rebuild it as an extension?
A new conservatory averages around £15,000 in 2026, while a solid extension costs roughly twice as much per square metre. You pay the premium for foundations, insulation and a structure that is usable every day of the year. The trade-off is straightforward: a conservatory is cheaper now, but a brick or block extension is comfortable in all seasons, lower maintenance, and counts as genuine living space when your home is valued or sold.
If you are weighing up the wider decision of how to add space, a rear or side-return extension is not the only route. A loft conversion adds a room without using garden space, and a basement conversion can work where outward space is limited.
Before and after: a real conservatory-to-extension project
The clearest way to picture the change is to see it. Below is a typical Build Team conservatory-to-extension conversion in London.
The project at a glance:
- The problem: a 16 m² uPVC conservatory that was unusable for half the year and added nothing to the home’s valuation.
- The work: conservatory removed, new insulated foundations, solid walls and a warm flat roof with a large rooflight, opened through to the kitchen.
- The result: a year-round open-plan kitchen and dining space, completed in around 10 weeks.
You can see more finished work in our extension project gallery.
Do I need planning permission to replace a conservatory with an extension?
Often not. Conservatories and extensions are treated the same way for planning, so a like-for-like replacement of a similar size usually falls under Permitted Development and needs no planning application. Even so, it is worth applying for a Lawful Development Certificate as proof for a future sale or mortgage.
Under Permitted Development rules in England, a single-storey rear extension can extend up to 3 metres beyond the original rear wall for a terraced or semi-detached house, or 4 metres for a detached house. The Larger Home Extension route can take this to 6 and 8 metres, subject to a neighbour-consultation process. Full planning permission is required if your home is a flat or maisonette, is listed, or sits in a conservation area, and where an Article 4 Direction has removed Permitted Development rights. The current householder application fee in England is £548 (from April 2026). Always confirm the position with your local authority, and read more on why planning applications get refused before you submit.
What building regulations apply?
This is where a conservatory and an extension differ most. A conservatory is usually exempt from Building Regulations, because it is thermally separated from the house by external-quality doors and windows, separately heated, and largely glazed. The moment you remove that separation and open the space into the home, it becomes part of the dwelling and full Building Regulations apply.
That means the new space must meet Part L for energy efficiency, which sets insulation and glazing standards, along with the requirements for structure, ventilation, drainage and safety glazing. As a guide, glazing should not exceed about 25% of the new floor area to control heat loss, and roof and wall insulation must hit current Part L values. The Future Homes Standard, with its Approved Documents published in 2026, raises new-build fabric standards further from 2027, and extensions already have to meet current Part L today. In practice this is exactly why an old conservatory cannot simply be opened up: it has to be insulated, reglazed and, often, refounded to comply.
Will replacing a conservatory add value to my home?
Yes, in most cases. A good-quality extension typically adds around 5 to 10% to a property’s value, and often more in high-value London areas. Nationwide’s house-price research found that adding around 10% to a home’s floor space lifts its value by roughly 5%, rising to as much as 24% where the project adds a substantial double bedroom and bathroom to a smaller house.
There is a second, often-missed point. A poorly insulated conservatory can be valued at little or nothing as habitable space by a surveyor, and can drag down your home’s EPC rating. Replacing it with an insulated extension turns dead floor area into space that counts, and improves your energy performance at the same time.
How long does the work take?
Most single-storey conservatory-to-extension projects take between 8 and 12 weeks on site, with the conservatory removal taking only a day or two at the start. Design and, where needed, planning approval happen before that, so allow a few months from first conversation to finished room. A fixed-price design and build contract is the surest way to keep the budget and timeline predictable.
Technical points worth checking early
- Foundations: existing conservatory footings are usually too shallow for a solid extension, so budget for a structural assessment and possible new foundations.
- Dwarf wall: the existing low wall is often uninsulated and may need insulated studwork or rebuilding as a cavity wall.
- Drainage: new connections must comply, and building over or near a drain may need approval from the water authority.
- Party Wall etc. Act 1996: if you build on or near a shared boundary, you will need to notify neighbours and may need a party wall agreement.
Frequently asked questions
How much does it cost to convert a conservatory into an extension in London?
Expect £2,800 to £5,500 per m² for the build in 2026, plus £800 to £2,500 to remove the old conservatory. A small-to-medium replacement usually totals £60,000 to £150,000 all in, with professional fees adding 10 to 15% on top.
Do I need planning permission to replace a conservatory with an extension?
Usually not, if the replacement is a similar size, as it tends to fall under Permitted Development. Full planning permission is needed for flats, listed buildings, conservation areas, or where Permitted Development rights have been removed. A Lawful Development Certificate is recommended as proof.
Can I reuse my conservatory’s foundations?
Sometimes, but only if a structural engineer confirms the existing base and dwarf wall can carry a solid, insulated structure. Conservatory footings are usually shallow, so many projects need new foundations.
Is an extension warmer than a conservatory?
Yes. An extension is built to current Part L insulation and glazing standards and is connected to the home’s heating, so it stays comfortable all year, unlike a glazed conservatory that overheats in summer and loses heat in winter.
How long does it take to replace a conservatory with an extension?
Around 8 to 12 weeks on site for a single-storey project, plus design and any planning approval beforehand.
Does replacing a conservatory add value to a house?
Typically around 5 to 10%, and often more in London. It also improves your EPC rating and turns space a surveyor may have valued at nothing into genuine habitable floor area.
Thinking of replacing your conservatory?
Build Team is a London design and build extension specialist. We handle everything from the first feasibility check and design through to construction, with a fixed price agreed before work starts.Or call 020 7495 6561 · email hello@buildteam.com
