Conservatory or Extension, Priced Side by Side
These are not two versions of the same job. One is an exempt structure with its own roof, priced by size band. The other is a heated room on foundations, priced by the builder who digs them. The gap is roughly four times, and it narrows only when you start specifying a conservatory to extension standards. This page is written from the conservatory side, because that is the side we hold data on.
Average conservatory · against a small single-storey extension · installed inc VAT
£9,000 to £18,000 against £40,000 to £56,000
Mixed gradesOne publisher, one date, both sides: a national cost publisher, October 2024. Across five publishers the conservatory band widens to £9,000 to £25,000, typical £15,000, Well evidenced. No UK source publishes an extension price table we can grade. Checked 20 August 2026.
The two jobs side by side
The conservatory column comes first because it is the column we can evidence. Every figure in it traces to a named publisher with a date. The extension column is thinner and the table says so on the row where it matters, rather than in a footnote.
| What you are comparing | Conservatory | Small single-storey extension |
|---|---|---|
| Published band, like for like | £9,000 to £18,000 | £40,000 to £56,000 |
| Band across every publisher we hold | £9,000 to £25,000, typical £15,000 | not published as a table anywhere we found |
| Evidence grade | Well evidenced, five publishers | Thin evidence, one framing line |
| Sources | Five UK cost publishers, dated Jun 2026, 12 May 2024, 28 Jan 2025, 29 Jul 2025 and 24 Jun 2026 | One national cost publisher, October 2024, one line inside an orangery guide |
| What the structure is | Mostly glazed walls and its own glazed or solid roof, on a light base | Masonry walls and a tiled or flat roof, on dug foundations |
| Building regulations | Usually exempt while it stays thermally separated and under 30 m² | Fully regulated work, no exemption available |
| Heating | Must not take the house heating system without the extension being assessed | Heated and insulated as part of the dwelling |
| What it is really bought for | Light and a garden view at a price a family can reach | Permanent floor area that counts as part of the house |
Sources: five UK cost publishers, one conservatory cost guide (June 2026, £9,000 to £18,000), then 12 May 2024 (£9,000 to £25,000), 28 January 2025 (£10,000 to £29,250), 29 July 2025 (£13,950 to £26,650) and 24 June 2026 (stated average £15,000), plus one national cost publisher's October 2024 three-way framing line for the extension figure. The Building Regulations positions are from Schedule 2 Class 7 of the Building Regulations 2010 and the LABC solid-roof addendum. Checked 20 August 2026.
Is it cheaper to have a conservatory or extension?
A conservatory, by a wide margin, and the margin is roughly four to one. On the only pair of figures published by one source on one date, a conservatory is £9,000 to £18,000 and a small single-storey extension is £40,000 to £56,000 (one national cost publisher, October 2024, checked 20 August 2026). Take the conservatory figure across all five publishers we hold and it becomes £9,000 to £25,000, typically £15,000, Well evidenced. Even at the top of that band the extension is still around twice the money.
The interesting part is that the gap is not fixed. Almost everything that makes a conservatory usable all year moves it towards the extension: a solid roof instead of glass, real insulation, a heated envelope, proper foundations. A conservatory built to that standard has stopped competing with a glasshouse and is being priced by the same trades as an extension. You can price your conservatory against your own size band first, then decide which conversation you are actually having.
The reverse move exists too and it is priced badly. The only figure we found for rebuilding an existing conservatory as a full extension is £15,000 to £25,000, from one national cost publisher in May 2024. We publish it as an anchor and nothing more: it is a single line with no size, no specification and no second source, so it carries no evidence grade. Checked 20 August 2026.
Why the extension half of this page is thinner
Our price register holds 222 rows. Not one of them prices an extension. The £40,000 to £56,000 above is a framing sentence inside somebody else's orangery guide, published once, in October 2024. It is real and it is current enough to quote, but it is one publisher with no size table, no per square metre rate, no regional split and no breakdown, so it is graded Thin evidence and it will stay Thin until three sources publish an extension table we can reconcile. Checked 20 August 2026.
We could have hidden that by averaging it with something. We have not. A number with one source behind it should look different from a number with five, so the conservatory side gets a band, a typical, a grade and five dated publishers, and the extension side gets one line and a warning. The asymmetry is the finding.
One conservatory figure is deliberately kept out of the band above. A premium national installer publishes a from-price of £27,000 for any style at 3m by 3m with no opening into the house, which is around 2.6 times the market for the same footprint. It is a genuine outlier rather than an error, so it is published as its own labelled row on our register and never blended into an average or into anything this site calculates. Checked 20 August 2026.
What each one comes to per square metre
A whole conservatory build runs £1,500 to £2,000 per m² all in, Thin evidence from one publisher, 28 January 2025. Strip out the base, the fitting and the making good and the structure alone is £875 to £1,050 per m² across four styles, Thin evidence from a second publisher, 24 June 2026. The distance between those two numbers is the clearest published evidence of how much of a conservatory price is not the conservatory. Checked 20 August 2026.
We hold no per square metre rate for an extension at all, so the honest comparison stops here rather than continuing with an invented divisor. Per square metre rates in this niche are unreliable in both directions anyway: they spread up to ten times across publishers, and none of them states whether the rate includes the base, building control or scaffolding. We publish ours as a cross-check on the size-banded totals and never the other way round. The full working is on conservatory cost per square metre.
At the small end the gap is widest
The four-to-one ratio is not constant across sizes. A lean-to at 3m by 3m is £8,000 to £13,000, typically £10,000, Reasonably evidenced from two publishers four months apart which agree exactly on the £8,000 floor, dated July 2026 and April 2026. Checked 20 August 2026. Nobody builds a 9 m² masonry extension for a quarter of that, because the fixed costs of an extension, the foundations, the structural opening and the regulated inspection regime, do not shrink with the floor area.
That is why small jobs are where a conservatory wins most decisively and large ones are where the argument gets genuinely close. What a small build actually contains, size band by size band, is set out at small conservatory cost.
Where the rules diverge
This decides the price long before the quote does. A conservatory can sit outside the Building Regulations entirely, under Schedule 2 Class 7, while it stays at ground level, under 30 m², separated from the house by external-quality doors and glazed to a significant proportion. An extension has no such route: regulated work from the first spadeful, with foundations, insulation, structural calculations and inspections priced in.
The exemption is conditional, not permanent. An exempt conservatory must stay thermally separated. Extending the house heating into it, which installers do routinely, is the commonest way a conservatory quietly stops being exempt, and it is regulated work at that point. Building Regulations 2010 Schedule 2 Class 7 and the LABC solid roof addendum, May 2018.
Planning permission is the other divergence, and it runs the opposite way from what people expect: a conservatory usually falls under permitted development within stated size limits, while an extension frequently does not. The size limits, and what happens either side of them, are on how large a conservatory can be without planning permission.
Price your conservatory
Six questions, about sixty seconds, and an estimate built from the rows above with every source shown.
This page compares two jobs. What yours comes to turns on your size band, your style and where you live, and our estimate is banded by size rather than multiplied out of a flat rate. Use see what yours would cost, or compare local conservatory roof installers if you already have a conservatory and the roof is the real problem.
Check what your conservatory will cost
We are paid when an installer quotes you. That is the whole business model and it is why the extension figure on this page carries a warning instead of a headline.
Does either add value?
Both can add value in the way any extra usable room can. Neither reliably adds it in proportion to what it cost, and the two behave differently at survey: an extension counts as floor area, a conservatory usually does not. We keep the evidence for that claim on one page rather than repeating a number here we cannot grade, so read whether a conservatory adds value before you treat either job as an investment.
If neither is quite the job
A middle option sits between the two on price and on rules, at £30,000 to £35,000 for 16 m², Reasonably evidenced from three publishers, checked 20 August 2026. Part-solid, part-glazed, and treated as an extension rather than an exempt structure. The full side by side is on orangery against conservatory cost.
There is also a word problem worth clearing up before you read any quote. Some products are sold under names that are not legal categories at all, and one of them usually just means a conservatory with a solid roof. Which product you are being sold is set out at conservatory or sunroom.
And if the honest answer is that neither of these two jobs fits the budget, there are cheaper routes that sit well below both figures. Every one of them is costed, with its own range, source and evidence grade, at conservatory alternatives, priced.
Questions people ask first
Is a conservatory always cheaper than an extension?
Why is your extension figure so much vaguer than your other numbers?
Do I need building regulations approval for a conservatory?
Can I turn a conservatory into a full extension later?
Which one adds more usable space per pound?
Every figure on this page was last checked 20 August 2026, next check due 20 November 2026. Where a figure comes from a single publisher we grade it Thin, and the extension side of this comparison is Thin throughout. For the same conservatory rows applied to your own size band, see our conservatory cost calculator.
Find out what yours costs
Six questions, about sixty seconds, and an estimate built from published UK figures with every source shown. Then up to four local installers can quote you, if you want them to.