Orangeries and Garden Rooms in London: Planning, Costs, Design 2025

The three categories — orangery, conservatory, and glazed extension — are most clearly distinguished by the proportion of glazing to solid wall and roof structure: Conservatory: defined under current Building Regulations (Part L) as a structure where more than 75% of the roof is glazed and more than 50% of the walls are glazed. The defining characteristic is the majority-glazed enclosure. Conservatories below a certain size threshold have historically been exempt from the energy performance requirements of Part L — but this exemption was removed in June 2022 for new conservatories that are heated or have openings to the main house. All heated conservatories built after June 2022 must meet the same thermal performance requirements as any other extension. Orangery: the term "orangery" refers to a partially glazed structure — typically with solid masonry walls at the base level and a glazed roof (often a flat or low-pitched lantern roof rather than a full glass roof). The orangery's structural brick or masonry walls distinguish it from a conservatory and make it a warmer, better-insulated, and typically better-finished space. An orangery is essentially a masonry extension with significant roof glazing — it is designed to feel like part of the house rather than a separate glazed appendage. For Building Regulations and planning purposes, an orangery is treated as a conventional extension (not as a conservatory). Garden room (insulated garden room): a freestanding insulated timber or steel-frame building in the garden, typically fully insulated and finished to habitable standard, used as a home office, garden studio, gym, or additional reception room. A freestanding garden room is not attached to the main house structure (though a covered pathway or glazed link may connect it), and may be constructed under permitted development if within the permitted development volume limits for outbuildings (Class E PD rights). Glazed extension: any extension to the main house that incorporates significant glazing — a rear extension with full-height bifold doors and a roof lantern, for example. This is the most flexible category and is designed and priced as a conventional masonry or structural steel extension with specialist glazing elements.

The planning treatment of an orangery, garden room, or glazed extension in London depends on the specific type, size, location, and whether the property is in a conservation area with an Article 4 Direction: Glazed extensions and orangeries attached to the main house: planning permission is required in most inner-London conservation areas (Article 4 Direction removes Class A PD rights for rear extensions). Outside a conservation area with an Article 4 Direction, a rear extension (including a glazed extension or orangery) may be permitted development under Class A GPDO 2015, subject to the standard limits: up to 3m beyond the original rear wall (for a terraced or semi-detached house); single storey; maximum height 4m at the ridge; maximum eaves height 3m within 2m of the boundary. Prior Approval for larger extensions (up to 6m for terraced/semi-detached, 8m for detached): the Prior Approval neighbour consultation scheme (under Class A of the GPDO 2015) allows larger single-storey rear extensions than the standard PD limits, subject to notification of the LPA and neighbour consultation. The LPA must be notified before works start, and the works can proceed after 42 days if no objections are received from affected neighbours. For a glazed extension or orangery in this category, this is the appropriate route where the extension size exceeds the standard PD limits but is within the Prior Approval limits. Conservation areas: in conservation areas with Article 4 Directions, all rear extensions (including orangeries and glazed extensions) require full planning permission, regardless of size. The design must be sympathetic to the conservation area's character — glazing-dominant rear extensions are typically accepted in conservation areas where they are not visible from the public realm and use slim-profile aluminium or timber frames. Freestanding garden rooms: a freestanding insulated garden room within the curtilage of a dwelling is typically permitted development under Class E of the GPDO 2015 (outbuildings PD rights), subject to: not exceeding 4m ridge height (dual pitch) or 2.5m eaves height; not covering more than 50% of the curtilage area; not located forward of the principal elevation. In a conservation area, Class E PD rights may be restricted by Article 4 Directions — check with the LPA before constructing a garden room in a conservation area.

The key design decisions for a London orangery or glazed extension are: Roof structure and glazing: the roof is the defining design element of an orangery or glazed extension. Options include: Full glass roof (single or double pitch): maximum natural light, but highest heat loss and solar gain. Requires external solar control glass (solar control coating, low-e coating) and may require mechanical ventilation or opening rooflights to manage summer overheating. Full compliance with Part L thermal requirements if the extension is heated and connected to the house. Roof lantern on a flat roof: a structural flat roof (insulated SIP or structural concrete) with a central roof lantern. This is the most common orangery roof design — it provides excellent natural light overhead while the insulated flat roof provides thermal performance. Costs: a quality aluminium roof lantern (1.5m x 1.5m) starts from approximately £3,000 supply only; a bespoke timber lantern can cost £8,000-£30,000. Flat warm roof (no lantern): a fully insulated warm flat roof without glazing — the lightest form of extension roof structure. Maximum thermal performance at minimum cost, but no overhead natural light. This is the standard specification for a rear kitchen extension rather than an orangery. Structural frame options: Aluminium structural system (e.g., Korniche, Ultraframe, Schuco, Kawneer): modern slim-profile aluminium structural systems allow large expanses of glazing with minimal frame visibility. High-specification aluminium systems can achieve a frame-to-glass ratio as low as 15-20% of the elevation area. Timber structural frame: a hardwood or softwood structural frame with glazed infill panels. Warmer appearance than aluminium, but requires periodic maintenance (painting or oiling). Steel structural frame: for the most architecturally demanding glazed extensions, a structural steel frame with bespoke glazing panels provides the maximum flexibility of form and the slimmest possible structural sections. Bifold doors and frameless sliding doors: the connection between the orangery and the garden is typically provided by bifold doors (which fold back in sections to create a fully open aperture) or large frameless or slim-frame sliding doors. Bifold doors for a 3m wide opening: £3,000-£8,000 supply only (aluminium). High-specification frameless sliding doors (Vitrocsa, Schuco, Dumawall): £10,000-£30,000 for a 3-4m opening supply only.

The cost of an orangery or glazed extension in London in 2025 varies significantly depending on the specification: Budget to mid-range glazed extension (aluminium bifold doors, roof lantern, masonry walls, insulated flat roof, mid-range finishes): 15-20 sq m extension, all-in: £40,000-£75,000. This is essentially a rear masonry extension with high-quality glazing elements and a roof lantern. Mid-range to high-specification orangery (slim-profile aluminium frame, quality glazing system, bespoke roof lantern, tiled floor with underfloor heating, quality internal finishes): 15-20 sq m, all-in: £75,000-£140,000. High-specification glazed extension or orangery (bespoke frameless glazing system, structural steel frame, triple-glazed units, automatic rooflights, automated bifold/sliding doors, underfloor heating, high-quality flooring and finishes): 15-20 sq m, all-in: £120,000-£200,000+. Garden room (freestanding, insulated, habitable): 15-20 sq m, all-in: £25,000-£60,000 (manufactured garden room) or £35,000-£80,000 (bespoke architect-designed garden room). What drives the cost difference: the glass specification (double vs triple glazed, solar control coatings, anti-reflective coatings); the frame system (budget aluminium vs slim-profile high-specification aluminium vs bespoke timber or steel); the roof system (standard roof lantern vs bespoke lantern vs full glass roof); the internal finishing specification (underfloor heating, quality tiling, bespoke joinery); and the extent of builder's work required (structural works to the existing rear wall, drainage, M&E).