Conservatory vs Extension: Which Should You Build?

Much cheaper to build: £12,000 to £30,000 for a conservatory against £45,000 to £90,000 for a single-storey extension. The honest comparison is cost per usable month. A uPVC conservatory is uncomfortable in high summer and cold from November to March, so you're paying for a room that works eight months a year. An extension is insulated, heated as part of the house, and works twelve. Cheap to build and cheap overall aren't the same thing.

Very little, and that surprises people. Surveyors don't count a conservatory as habitable floor area, so it barely moves a valuation — you might see 2 to 4% on an attractive one against a build cost that often exceeds that. An extension adds real floor area, which is what drives London valuations, and a well-judged one adds more value than it costs. If adding value is the goal, the conservatory isn't the route.

An orangery is the middle option: solid insulated walls with a flat roof and a glazed roof lantern, rather than a conservatory's glass walls and glass roof. The solid construction means it holds heat like a normal room and works in January with ordinary radiators or underfloor heating. Cost-wise it sits between the two, typically £30,000 to £55,000 in South London. Surveyors treat a well-built orangery much closer to habitable space than a conservatory, so more of the spend comes back at sale time.

Usually neither does, within limits. Both typically fall under permitted development: up to 3 metres from the rear wall on a terraced house, 4 on detached, with height limits. The difference is Building Regulations. A conservatory is exempt if it stays separated from the house by external-quality doors and has its own heating controls; remove those doors to open it up and it must meet full Building Regulations like any extension — which most conservatories can't. Extensions and orangeries go through Building Control as standard, which is part of why they count as real rooms.