Conservatories and Orangeries in London: Planning, Construction, and What to Specify

The conservatory and the orangery occupy the same broad category — a glazed extension that blurs the boundary between interior and garden — but they differ significantly in character, construction, and cost. Understanding the distinction, and what each requires from a planning and structural standpoint, helps clients make the right choice for their property.

Conservatory versus orangery: the distinction

Conservatory: A structure where the majority of the roof and walls are glazed, typically in aluminium or uPVC framing. The glazed roof is the defining characteristic. Conservatories are predominantly glass, lightweight, and less thermally efficient than the main house.

Orangery: A masonry or part-masonry structure with a glazed roof lantern or rooflight section, substantial walls, and a more architectural quality. The orangery reads as an extension to the house rather than a glass box appended to it. Thermally and structurally, an orangery performs similarly to the rest of the house.

The practical distinction matters: a conservatory is typically excluded from building regulations requirements for thermal performance (if it meets specific conditions) and is simpler to construct. An orangery is subject to the same Part L requirements as any other extension and is typically a more complex, more expensive build.

Planning permission

Conservatories under permitted development: A conservatory can be built under permitted development subject to the same limits as other single-storey rear extensions (3m projection for terraced/semi-detached, 4m for detached, or up to 6m/8m under the Neighbour Consultation Scheme). The specific exemption for conservatories from Part L thermal requirements applies when:

• —It is separated from the house by external-quality walls, doors, or windows
• —It has an independent heating system (or no fixed heating)
• —It is at ground level

In practice, most well-specified conservatories are now designed to be thermally integrated with the house — which removes the Part L exemption but produces a much better living space.

Conservation areas: In a conservation area, a conservatory visible from the street requires planning permission. On the rear of a terrace, not visible from the public realm, PD rights typically apply subject to normal volume limits.

Listed buildings: Listed building consent is required for any addition to a listed building. A glazed conservatory on a listed building is not automatically refused — well-designed, reversible, lightweight structures have been approved on listed buildings — but the design must be argued carefully against the test of preserving the building's character.

Structural approach

Conservatory on a dedicated base: A shallow strip foundation or raft foundation beneath a low brick or blockwork dwarf wall, supporting the aluminium or timber conservatory frame. For a standard conservatory, this is simple and inexpensive.

Orangery/extension with roof lantern: Full strip or pad foundations, masonry walls, and a structural roof — either flat with a central rooflight lantern or pitched with glazed sections. The structural design is similar to any other masonry extension. The roof lantern is a specialist element — slimline aluminium or structural glass — sourced from manufacturers such as Roof Maker, Velux (corporate/commercial range), or IQ Glass.

Steel-framed structure: For a wide-span glazed structure (over approximately 5m in any direction), a structural steel frame is typically required. The steel allows large spans without intermediate columns and permits the extensive glazing that creates the light-filled aesthetic clients expect. Steel-framed glazed extensions require a structural engineer's design.

Glazing specification

The glazing in a conservatory or orangery is the largest determinant of thermal performance, solar gain, and long-term usability.

Roof glazing: The most critical area. A poorly specified conservatory roof will overheat in summer and lose heat rapidly in winter, making the space unusable for much of the year. Key specifications:

• —*U-value*: Current Part L requires roof glazing to achieve 1.6 W/m²K or better. For a roof that will perform comfortably, target 1.0–1.2 W/m²K with triple glazing or specialist coated glass.
• —*Solar control coating*: A low-solar-gain glass (g-value 0.35 or below) significantly reduces summer overheating. Essential for south- or west-facing roof glazing.
• —*Self-cleaning glass*: A photocatalytic coating (Pilkington Activ, SGG Bioclean) breaks down organic dirt in UV light and is washed clean by rain. Recommended for any roof glazing that cannot easily be accessed for manual cleaning.

Wall glazing: Bifold or sliding doors (Schüco, Reynaers, IQ Glass) achieving U-value 1.4–1.6 W/m²K with thermally broken frames. Fixed glazed panels to match.

Thermal mass and heating

A conservatory or orangery performs best when it has adequate thermal mass (the ability to store and slowly release heat). Masonry walls, stone or tile floors, and thick glazing all contribute. A lightweight uPVC conservatory on a thin concrete base has minimal thermal mass and will temperature-swing dramatically.

For an orangery that will be used as habitable space throughout the year, specify:

• —Underfloor heating (electric or wet, depending on how the extension connects to the house system)
• —Roof glazing with high thermal performance (triple glazed or specialist coated)
• —Adequate ventilation — automatic opening vents in the roof to prevent summer overheating

Realistic costs

These figures include structure, glazing, floor, and basic finishes. They exclude furnishing, landscaping, and the connection/infill works between the new structure and the existing house.

ASAAN has designed and built glazed extensions and orangeries as part of London renovation programmes. Our team manages structural engineering, glazing specification, and building control approval as part of a single coordinated project.