Choosing between an orangery, a conservatory and a full extension is one of the first decisions you’ll face when planning extra living space. The right answer depends on budget, how you’ll use the room, and how much disruption you’re prepared to tolerate during the build. This guide cuts through the marketing to give you an honest comparison of all three.
Definitions: What Exactly Are You Buying?
Conservatory
A conservatory is predominantly glazed — typically more than 50% of its wall area and more than 75% of its roof area must be translucent or transparent for it to qualify for the planning exemption under Schedule 2, Part 1 of the Town and Country Planning (General Permitted Development) (England) Order 2015. In practice this means a timber or uPVC frame with polycarbonate or glass panels and a lean-to or Victorian-style ridge roof. Good for a garden room or plant-filled retreat; less suitable as a year-round living room without expensive climate control.
Orangery
An orangery sits between a conservatory and a full extension. It has solid brick or rendered piers at the corners, a flat roof lantern (rather than an all-glass pitch), and typically 30–50% glazing across its walls. The term has no strict legal definition, but most planning authorities treat an orangery as a solid extension, which means Building Regulations Part L (energy efficiency) and Part A (structure) almost always apply.
Single-Storey Extension
A full bricks-and-mortar (or timber-frame) extension has solid walls, a tiled or flat roof, and only as much glazing as you choose. It is the most thermally efficient option by default and the most flexible in terms of layout. It is also subject to the full Building Regulations suite — Parts A, B, C, F, L, and often P.
Cost Comparison
Prices below are 2026 installed costs including VAT for a typical rear single-storey addition of approximately 20 m² in southern England. Costs in the Midlands and North are typically 10–20% lower.
| Option | Low (£) | Typical (£) | High (£) | Per m² (typical) |
|---|---|---|---|---|
| Polycarbonate conservatory | 12,000 | 20,000 | 35,000 | £1,000 |
| Glass-roof conservatory | 18,000 | 28,000 | 45,000 | £1,400 |
| Orangery | 28,000 | 45,000 | 70,000 | £2,250 |
| Single-storey extension (brick) | 40,000 | 65,000 | 110,000 | £3,250 |
| Single-storey extension (timber frame) | 35,000 | 55,000 | 90,000 | £2,750 |
The wide ranges reflect specification choices: bifold vs French doors, underfloor heating, kitchen or utility fitout, and roof lantern quality. An orangery with a structurally insulated flat roof and frameless glass lantern will approach the cost of a modest brick extension.
Planning and Building Regulations
Permitted Development (England)
Under current Permitted Development rights (as of 2026), a single-storey rear addition may be built without a planning application if:
- It does not extend beyond the rear wall of the original house by more than 4 m (detached) or 3 m (semi-detached or terrace).
- Height does not exceed 4 m at the ridge or 3 m at the eaves where within 2 m of the boundary.
- It does not cover more than 50% of the garden area.
The “Larger Home Extension” prior approval process (introduced in 2019 and made permanent in 2020) allows up to 8 m (detached) or 6 m (semi/terrace) under a neighbour consultation scheme — the local authority must be notified and has 42 days to assess any objections.
Conservatories are additionally exempt from Building Regulations (under Regulation 9 and Schedule 2 of the Building Regulations 2010) provided they are thermally separated from the house by an external-quality door and their heating is independently controlled. Remove either condition and you lose the exemption.
Orangeries and extensions always need Building Regulations approval. Apply for either a Full Plans application (drawings submitted up front, inspected at stages) or a Building Notice (quicker but no approved drawings — higher risk). Full Plans is strongly recommended for any project over about £20,000.
Conservation Areas and Listed Buildings
All three structures require full planning consent if the property is listed. In a designated Conservation Area, permitted development rights for side extensions are removed entirely; rear extensions may still apply but you should pre-check with the local planning authority.
Thermal Performance
This is where the three structures diverge most sharply in day-to-day usefulness.
| Metric | Polycarbonate conservatory | Double-glazed glass conservatory | Orangery (2026 spec) | Brick extension |
|---|---|---|---|---|
| Typical summer peak temp (°C above ambient) | +10 to +15 | +6 to +10 | +2 to +4 | ±1 |
| Winter heat loss (W/m² at -5 °C outside) | ~80–100 | ~50–65 | ~20–30 | ~8–12 |
| Typical annual heating cost (20 m²) | £600–£900 | £350–£550 | £150–£250 | £80–£130 |
A polycarbonate conservatory is essentially an outdoor space made waterproof. Modern triple-glazed conservatories with warm-roof insulated panels close the gap considerably, but they cost as much as a modest orangery. An orangery with a 0.15 W/m²K insulated flat roof and A-rated double glazing is genuinely usable year-round without supplementary heating in most UK climates.
Part L of the Building Regulations (Conservation of Fuel and Power, 2021 update) sets maximum U-values for new extensions: walls ≤ 0.28 W/m²K, roofs ≤ 0.16 W/m²K, glazing ≤ 1.4 W/m²K. Extensions must comply; qualifying conservatories are exempt.
Resale Value
No independent UK study has established a definitive uplift figure, but the general consensus from RICS-registered surveyors is:
- A well-built brick extension adds roughly 5–15% to property value depending on local comparable evidence and whether it adds a usable bedroom or living space.
- An orangery is regarded as a premium feature and can add 4–8%, though it is harder to appraise because comparables are scarcer.
- A conservatory adds value only if it is in good condition and thermally comfortable. A tired polycarbonate conservatory can actively deter buyers or require a price reduction.
The quality of finish and integration with the existing house matters more than the structure type. A well-designed orangery that flows from the kitchen will outperform a poorly detailed extension with a clashing roofline.
Which Should You Choose?
Choose a conservatory if: your budget is under £25,000, you want a garden-adjacent space primarily for warmer months, and you don’t need planning flexibility beyond the standard PD envelope.
Choose an orangery if: you want a year-round usable room with more thermal comfort than a conservatory but prefer a lighter, more open feel than a solid extension. Budget £35,000–£70,000 for a quality result.
Choose a full extension if: you need the space to function as a kitchen, dining room, bedroom, or bathroom; if you want maximum thermal efficiency; or if you plan to build over two storeys. Budget from £40,000 upwards for a meaningful 15–25 m² addition.
In any case, instruct a RIBA architect or qualified designer for the drawings and specification — the fee (typically 8–15% of construction cost) pays for itself in avoiding costly changes during the build and in obtaining realistic contractor quotes.
