An orangery is priced like a small extension with a great deal of glass in it, which is why per square metre figures for conservatories do not transfer. The base is a real foundation, the piers are masonry, the perimeter roof is an insulated flat roof, and the lantern is a substantial glazed unit with a kerb under it.
How much is an orangery extension? What the money is buying
Groundworks and foundations to the depth the ground requires. The masonry piers and any parapet, in brick to match the house. The glazing between the piers. The flat perimeter roof, insulated as a warm deck with its falls and outlets. The lantern and the kerb it sits on. Then the fit out: floor build up and finish, plastering, electrics, lighting, heating, and the doors or opening into the house. The last group is routinely underestimated because it is not what the brochure photographs.
Why the ground moves the number most
As with any extension, foundation depth follows the soil and what is near it. Clay and nearby trees mean deeper. A drain or an inspection chamber in the footprint has to be dealt with properly, and building over or close to a public sewer needs the water authority's agreement. Sloping ground means stepping or building up the base. A price quoted from a size in metres has assumed all of it, which is why two quotes for the same room can be far apart before a single frame is priced.
Orangery roof cost: the lantern and the roof are their own budget
A lantern is a manufactured glazed unit whose price rises steeply with span, because the ridge bar has to carry itself. The kerb it sits on is carpentry and weathering work by somebody else. The perimeter flat roof needs designed falls, a warm deck build up and proper upstands. On many quotes the roof and lantern together approach the cost of the glazing, and a quote that does not separate them is hiding which of the two it has skimped.
Extension, orangery or conservatory: which costs more for the same room
It costs more than a conservatory of the same footprint and usually less than a fully conventional extension with the same amount of glazing, because a lantern is cheaper than forming a large rooflight in a conventional roof. Against a plain extension with ordinary windows it costs more. The comparison worth making is against an extension, not against a conservatory, because that is what it is regulated and built like.
What to insist a quote itemises
Foundation type and assumed depth and what happens if the ground requires more, how drainage in the footprint is handled, brick specification and pier construction, glazing specification, the perimeter roof build up and its insulation, the lantern size and specification and who builds the kerb, the internal finishes, electrics and heating, and who certifies the work. A contract agreed in your home carries a statutory cancellation period, so a price that expires tonight is a sales device.
Questions people ask about orangery cost per m2
Is an orangery cheaper than an extension?
Usually a little, where the comparison is with an extension carrying similar glazing, because a lantern is a cheaper way to get light into the middle of a plan than forming a large rooflight. Against a plain extension it costs more.
Why do orangery quotes vary so much?
Mostly the base and the fit out. The frames and the lantern are the visible parts and the least variable; foundations, drainage and internal finishes are where the assumptions differ.
Is small orangery extension cost higher per square metre?
Generally yes. Fixed costs such as mobilisation, groundworks setup and the lantern do not scale down proportionally, so a small orangery has a higher rate per square metre than a large one.
Should I trust an orangery price calculator?
For a range only. It cannot see the ground, the drains, the access or what the fit out specification is, and those are exactly the variables that decide the final figure.