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Most conservatories fall under permitted development if under 30m2 and thermally separated from the house (external-quality doors between): heating a glass box from the house's system is what building regs exist to stop. The solid-roof retrofit is the industry's own admission: it converts the too-hot-in-July, too-cold-in-January room into one that gets used in both.
What The Conservatory Cost Calculator Works Out
- Estimated total: floor area multiplied by the rate for the style, plus a solid roof if chosen. The lean-to's simple mono-pitch starts around GBP 1,200/m2 supplied, fitted and based, Victorian and Edwardian bay-and-hip styles run GBP 1,400 to GBP 1,700, and orangery-style hybrids with brick piers and lantern roofs push past GBP 2,000 toward extension money. A 10 m2 conservatory lands between GBP 12,000 and GBP 20,000.
- Solid roof: replacing the glass or polycarbonate lid with an insulated one costs GBP 4,000 to GBP 8,000 and turns the conservatory into the garden-room-grade space it was bought as.
- The honest question: the conservatory buys maximum light and the fastest planning-free route to more floor; the garden room buys year-round insulation at similar money but detaches from the house; the extension buys a real room at roughly double.
- Running reality: single-purpose glass boxes gain July heat and shed January warmth. Extending the house's central heating into the space is exactly what Building Regulations restrict, which is why the room must be thermally separated by external-quality doors.
- Glazing upgrade (advanced): solar-control and self-cleaning glass adds around GBP 150/m2 and makes the biggest difference on a south-facing conservatory, which is a greenhouse with sofas unless specified against it.
- Heating (advanced): an electric radiator at about GBP 600 or electric underfloor heating at around GBP 100/m2, both legitimately independent of the house system.
- Blinds and groundworks (advanced): roof and side blinds commonly run GBP 1,000 to GBP 3,000 for a 10 m2 room; sloping sites, drain diversions and dwarf walls add groundworks that supplied-and-fitted quotes may exclude.
- Solid roof now vs later (advanced): the saving from fitting a solid roof at build time against the typical retrofit price you enter, since scaffolding and roof work are paid for twice if done later.
- Your best quote vs estimate (advanced): how far a real quote sits from this estimate, as a prompt to check what is itemised. The buying craft is the double-glazing playbook: multiple quotes, the theatrical first price declined, base and building work itemised, and FENSA or CERTASS certification for the glazing.