Technical definition: conservatory vs orangery
The distinction between a conservatory and an orangery is architecturally, legally and technically significant — not merely cosmetic. A conservatory is defined in planning and building regulations law by its roof: more than 75% of the roof area must be glazed or translucent. This is specified in Schedule 2, Class 7 of the Building Regulations 2010 and is implicit in the GPDO's treatment of conservatories as a distinct type of single-storey addition. The walls of a conservatory are typically mostly glazed as well, though there is no precise legal threshold for wall glazing — the critical test is the roof. An orangery is structurally a hybrid between a house extension and a conservatory. Its defining characteristics are: a solid insulated roof (typically comprising a warm roof build-up with insulation, membrane and lead or zinc standing seam cladding, or a flat roof with felt and gravel finish); a central lantern or rooflight providing overhead light; brick, stone or substantial timber pillar construction at the corners and between glazing bays; and an internal architectural cornice at ceiling level, which creates the characteristic 'room-within-a-room' feel. Architecturally, orangeries derive from the 17th and 18th century structures used to overwinter citrus trees at country estates — the Buckingham Palace garden orangery and many National Trust properties provide reference examples of the classical form. Modern London orangeries typically reinterpret these proportions in brick matching the existing house, with thermally broken aluminium or hardwood glazing frames. The lantern can be aluminium, timber-framed or structurally glazed (frameless), with sizes from 1.5m × 1.0m upwards.
Planning and building regulations: how the distinction matters
The conservatory/orangery distinction has direct legal consequences under both planning and building regulations. Under the GPDO (planning), both conservatories and orangeries are typically Class E PD-compliant additions provided the standard conditions are met (single storey, not forward of principal elevation, under 50% curtilage, correct height). The distinction does not affect planning eligibility in itself — an orangery can be PD-compliant just as a conservatory can. However, where planning is required (conservation areas, Article 4, flats), the design of an orangery often sits better with conservation officers because it reads more as a substantial architectural addition than a lightweight glazed box. Under building regulations, the distinction is decisive. A conservatory with a glazed roof meeting the 75% threshold, combined with thermal separation and a floor area under 30m², is exempt from Part L under Schedule 2 Class 7. An orangery with a solid roof never meets the 75% glazed roof threshold, and therefore full building regulations apply — Part L (thermal performance), Part A (structural), Part F (ventilation) and Part O (overheating) are all engaged. The practical consequence is that an orangery requires: a SAP Part L energy calculation, structural engineering sign-off on the new opening, building control inspections at foundation, structure and completion stages, and a completion certificate on handover. This adds approximately £2,500–£4,000 to project costs but delivers a better-performing structure. Builderr manages all building control submissions in-house.
Thermal performance and year-round usability
Thermal performance is where the orangery decisively outperforms the conservatory. A standard glazed conservatory with argon-filled double-glazed units (U-value 1.4 W/m²K walls, 1.8–2.4 W/m²K roof) loses heat rapidly in winter and gains solar heat rapidly in summer. Many London conservatories are unusable for three or four months in winter without supplementary heating running constantly, and for two or three months in summer without air conditioning. The 2021 edition of Part L (effective June 2022) has tightened performance requirements for regulated extensions — this is why modern solid-roof conservatories (which trigger Part L) are now built to a substantially higher standard than their glazed counterparts. An orangery built to current Part L standards will have: a solid insulated roof with U-value ≤0.15 W/m²K (typically 200mm PIR insulation in the roof build-up), wall U-values ≤0.18 W/m²K, floor U-values ≤0.13 W/m²K, and argon-filled low-E glazed units in walls and lantern achieving ≤1.2 W/m²K centre pane. An air-source heat pump cassette or multi-split unit providing both heating and cooling makes the space genuinely comfortable year-round for an all-in cost of £3,500–£6,000. A well-specified orangery in London should be usable without supplementary heating above 12°C outside temperature, and with cooling active, should not exceed 26°C internally on a typical London summer day. Solar-control glass with SHGC ≤0.35 on the lantern is critical for south and west-facing orangeries.
Cost, value and which adds more to a London home
An orangery costs 25–40% more than an equivalent-size conservatory. For a 20m² space, a conservatory typically costs £60,000–£80,000 (aluminium frame, standard glazing, no UFH) while an equivalent orangery runs £80,000–£108,000 (brick pillars, solid roof, lantern, UFH, Part L-compliant glazing). The additional cost is driven by: solid roof construction (higher material cost than glazed panels), structural brickwork at corners and piers, building regulations compliance (SAP, structural, building control fees), and the typical decision to specify higher-grade glazing when investing in a solid-roof structure. On the value uplift question, estate agents across London (Savills, Knight Frank, Foxtons) consistently report that an orangery adds more value per pound spent than a conservatory. The reasons are straightforward: orangeries are usable year-round without additional heating costs (a practical benefit buyers can immediately quantify), they read architecturally as room additions rather than temporary structures, and they are perceived as higher-quality additions in both the lettings and sales markets. In prime London postcodes (NW3, SW3, SW10, W11, N6), a well-specified orangery of 18–25m² typically adds £90,000–£150,000 to a property, delivering a value uplift that equals or exceeds the construction cost. In zones 3–4, the uplift is typically £40,000–£80,000 on a standard terrace. A lean-to conservatory in the same markets adds £20,000–£45,000 at best.
