Orangery, glass box or solid extension?
A solid extension is the warmest and cheapest per square metre, an orangery adds a large roof lantern and more glazing for light, and a glass box gives the most light and the lightest look but costs most, about £3,000 to £5,800 per m². Glass-heavy designs need careful thermal and solar design to meet the building regulations and stay comfortable.
How they compare
| Solid extension | Orangery | Glass box | |
|---|---|---|---|
| Guide cost per m² | £1,750 to £3,400 per m² | £2,400 to £4,500 per m² | £3,000 to £5,800 per m² |
| Daylight | Good with rooflights | Very good | Maximum |
| Winter warmth | Best | Good | Needs careful design |
| Summer overheating risk | Low | Moderate | Higher without shading |
The building regulations angle
In England, extension glazing is normally limited to 25% of the new floor area plus the openings it replaces. Orangeries can approach that limit and glass boxes exceed it, so they usually need whole-house energy calculations to show compliance.
Replacing a conservatory
If you have an old conservatory, replacing it with an orangery or solid extension gives a room you can use all year. See our conservatory replacement page.
This guide is general information, not legal or professional advice for your property. Rules can change; we check the current position for your address at the survey.