How Much Does an Orangery Cost?
A premium over a plain single storey extension of the same floor area, spent almost entirely above your head.
An orangery on reasonable ground with decent access runs £2,800 to £3,800 per square metre, so a 20 square metre room commonly lands between £56,000 and £76,000 of building work before VAT and fees. That is roughly £600 to £800 a square metre above a plain single storey extension, and the premium is the roof: masonry piers instead of a continuous wall, a perimeter ring beam tying them together, and a made to measure lantern standing on an insulated upstand. It costs several times a conservatory quotation because it is not exempt from Building Regulations. Exemption needs ground level siting, a floor area not exceeding 30 square metres, thermal separation from the house with independent heating controls and Part K glazing, and an orangery opened into the kitchen fails the separation limb.
£2,800 to £3,800 per square metre, so a 20 square metre orangery on reasonable ground with decent access commonly lands between £56,000 and £76,000 of building work. That is roughly £600 to £800 a square metre above a plain single storey extension of the same floor area.
Almost the whole of that premium is spent above your head. An orangery is a conventional extension for its first metre out of the ground and then diverges sharply, and the divergence is the roof and the glass in it.
Where the premium actually goes
Four items replace cheaper ones, and each of them costs more per linear metre than the thing it stands in for.
A plain extension has continuous cavity walls, a warm deck flat roof and a hole cut in the back of the house. An orangery swaps the continuous wall for masonry piers with glazed bays between them, ties the piers together with a perimeter ring beam, carries an insulated flat roof on that beam with a plastered pelmet at its edge, and stands a made to measure lantern on an insulated upstand in the middle of it.
None of those is a finish upgrade. The piers are point loads rather than a spread load, so the foundation beneath each one is doing concentrated work. The ring beam is a structural item that a plain wall does not need at all. The pelmet and the lantern upstand are the fiddliest plastering on the job. Take the lantern away and you have a slightly overbuilt extension paying for structure it is not using.
| A plain extension | An orangery | Why the premium |
|---|---|---|
| Continuous cavity wall | Masonry piers with glazed bays between them | Point loads, so concentrated work under each pier |
| No ring beam | A perimeter ring beam tying the piers together | Structure a plain wall does not need at all |
| A warm deck flat roof | The same roof on that beam, with a plastered pelmet | The fiddliest plastering on the job |
| No lantern | A made to measure lantern on an insulated upstand | Priced by glazed area, and four lines move together |
The lantern is priced by area, and area grows faster than dimensions
This is the one item on the quotation most worth pinning down in writing before anybody compares two prices.
Going from a lantern of 2 metres by 1.5 to one of 3 metres by 2 sounds like a modest increase. It doubles the glazed area, and it also enlarges the opening trimmed out of the roof deck, the insulated upstand around it, the plastered reveal below it and the structure carrying all of it. A bigger lantern is not a bigger version of one line on the price. It is four lines moving together.
So the specification needs three things stated: the finished size, the frame material, and the glass. A quotation that says “roof lantern to rear” is not comparable with anything.
The glass specification is physics, not a preference
A horizontal glazed roof takes the sun at its strongest, and an orangery lives or dies on how that was handled.
Solar control glazing in the lantern is not an upgrade to be trimmed out of the budget. Left out, the room is unusable through a July afternoon and the shell that held the warmth in through January holds it in then too. It carries a real cost and it is the item most often quietly downgraded between an initial figure and a final one.
The frames matter for the opposite season. A lantern is a run of bars crossing from a warm interior to a cold exterior, and unless those bars are thermally broken they will run with condensation on a still January morning and drip it onto whatever is beneath. There is more on how roof glazing is specified and where it goes wrong.
It is not a conservatory, and that is most of the price difference
The comparison people make is with a conservatory quotation, and the two are not the same regime.
A conservatory can fall outside Building Regulations control where it is at ground level, its floor area does not exceed 30 square metres, and any glazing satisfies the safety requirements of Part K. A separate rule then keeps the energy efficiency requirements off it, but only while it stays shut away from the house behind walls, doors or windows of external quality and is heated, if at all, on its own controls. That second rule is the one an orangery fails, because the whole point is to open it into the kitchen and leave it open.
Once it is open to the house it is an extension. That means an insulated floor, walls and roof built to current U-values, controlled ventilation, a structural opening designed and calculated, and Building Control from start to completion certificate. None of that appears on a conservatory quotation, and all of it appears here. If you are holding two prices that differ by a factor of three, that is what the gap is made of, not the brickwork.
What pushes it above the range
Deep foundations, which around Colchester means shrinkable clay and mature trees, and a piled solution beside a protected tree is a different order of cost. Access, because the perimeter beam, the glazed units and the lantern sections all need a route to the back of the house. A large structural opening into the existing rear wall, which is priced on its own at £3,000 to £8,000 or more depending on span and load. Underfloor heating, which suits a room with this much glass and has to be decided before the screed goes down rather than after.
What the rate excludes
VAT, kitchen units and appliances, floor finish, decoration, the drawings and structural calculations, planning and Building Control fees, a build over agreement where a public sewer runs under the footprint, party wall surveyor fees where a neighbour dissents, and landscaping afterwards. The full list, with what does sit inside a price, is on the extension costs page.
Turning the range into a figure
The lantern size, the glass, the foundation depth and the width of the opening into the house will between them account for most of the distance between the bottom of this range and the top. Every one of them is settled at survey and drawing stage, before anyone breaks ground, which is the whole argument for pricing the job that has been seen. How an orangery is built and which houses suit one covers the rest.
These figures are indicative for the Colchester area at the review date below and they move with materials and labour. Treat them as a way of sense checking a quotation rather than as a quotation.
Last reviewed August 2026.
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