Conservatory vs Orangery vs Glass Box: A Buyer’s Framework
A practical side‑by‑side comparison of cost, planning, thermal performance and decision factors – helping homeowners across Hampshire, Surrey, Sussex, Kent and London choose the right glazed extension.
The short answer: Conservatories maximise light and are generally most affordable; orangeries offer better thermal stability and feel more like a permanent house extension; glass box extensions deliver a contemporary, frameless aesthetic with premium cost and engineering. The right choice depends on your budget, site conditions, planning context and how you intend to use the space.
Quick comparison at a glance
Conservatory
Orangery
Glass Box Extension
1. Understanding the three options
Conservatory
A conservatory is defined under UK planning law as a structure with at least 50% of its side wall area glazed and at least 75% of its roof area covered by translucent material (glass or polycarbonate). Traditional styles include Victorian, Edwardian and lean‑to. Modern conservatories use low‑E glass, argon fill and warm‑edge spacers, making them comfortable for much of the year. Build time is typically 2–4 weeks and they are often the most budget‑friendly option.
Orangery
Historically built to protect citrus trees, an orangery sits between a conservatory and a traditional extension. It features a solid brick or masonry base, large windows above, and a flat solid roof with a central glass lantern. Less than 50% of the wall area is glazed, which means better thermal insulation and a more permanent feel. Build time: 6–12 weeks. Estate agents often perceive orangeries as adding more property value than a standard conservatory.
Glass Box Extension (Frameless/Structural Glass)
A glass box uses structural glass or slim‑frame aluminium systems (as narrow as 35–50mm) to create almost invisible boundaries between indoors and outdoors. True frameless systems rely on glass fins and structural silicone. These extensions require full Building Regulations approval, longer build times (10–20 weeks) and higher budgets, but deliver a striking contemporary aesthetic.
2. Cost breakdown (2026 UK data)
Cost figures are compiled from Hallmark Glazed Extensions, Room Outside, Everest, Ultraframe, MyJobQuote and independent surveys. Actual costs vary with site conditions, specification and location (London and South East carry a 20–30% premium).
| Option | Typical cost range (20m², 2026) | Notes |
|---|---|---|
| Conservatory (uPVC, glass roof) | From £48,000 | Basic specification, may have higher U‑value. |
| Conservatory (aluminium frames) | From £60,000 | Slimmer sightlines, better thermal breaks. |
| Orangery (standard) | £60,000–£85,000 | Brick base, standard roof lantern. |
| Orangery (premium) | £85,000–£115,000+ | New Generation Glass, improved insulation. |
| Framed glass extension | £50,000–£100,000 | Slim aluminium frames (35–50mm). |
| Structural glass box | £80,000–£180,000+ | Glass fins, bespoke engineering. |
Key cost drivers: foundations (clay soil or trees add £4k–£15k+), frame material (timber most expensive, uPVC most affordable), glazing specification (solar control adds 10–25%), and kitchen fit‑out (£15k–£45k extra).
3. Planning permission & Building Regulations
Permitted Development (PD): Conservatories and orangeries can often be built under PD if they do not exceed 4m height, 3m depth (semi/detached) or 4m (detached), and cover no more than 50% of the garden. Glass boxes are almost never exempt because they are not considered “conservatories” in the legal definition – they always require planning permission.
Building Regulations: A conservatory is exempt if all five conditions are met: under 30m², ground level, thermally separated, independent heating, and glazing safety. Orangeries and glass boxes generally require full approval, meeting current U‑value standards (walls ≤0.28 W/m²K, roof ≤0.16 W/m²K).
4. Thermal performance & year‑round comfort
Modern conservatories with solar‑control glass (g‑value ≤0.35) and thermally broken frames can be comfortable for much of the year, but they still have lower thermal mass than brick walls. Orangeries benefit from solid perimeter walls, which moderate temperature swings and often feel more stable. Glass box extensions rely entirely on glass specification – high‑performance units with low‑U and low‑g values can perform well, but occupants should expect quicker temperature changes than in an orangery.
5. Property value contribution
According to 2026 estate agent surveys (Homebuilding & Renovating, Which?): a quality conservatory typically adds 5–7% to a home’s value; an orangery can add 10–15% because it is perceived as a permanent extension. Glass box extensions, being less common, have less published data but can be a strong selling point for high‑end contemporary properties.
6. A buyer’s decision framework
Choose a conservatory if…
- Maximum natural light is the top priority
- Budget is moderate (£48k–£60k)
- You want a quick build (2–4 weeks)
- Use: dining, playroom, garden room, occasional office
Choose an orangery if…
- You want a permanent, solid feel
- Better thermal performance and sound insulation matter
- Budget: £60k–£115k+
- Use: kitchen, family room, home office, reception
Choose a glass box if…
- Contemporary, frameless aesthetic is essential
- Prepared for planning permission and longer build (10–20 weeks)
- Budget: £80k–£180k+
- Use: high‑end kitchen, living area, architectural home office
Explore Room Outside’s products & guides
External sources and further reading
Which? – Choosing an orangery | Homebuilding & Renovating – Orangery vs conservatory | Planning Portal – Permitted Development | Resi – Planning for orangeries | Everest – Orangery cost guide 2026 | IQ Glass – Glass box extension guide
Frequently asked questions
Which is cheaper: conservatory, orangery or glass box?
A conservatory is generally the most affordable option, with entry-level prices from around £48,000 for a 20m² build. Orangeries typically cost from £60,000 upward, and structural glass boxes often start above £80,000.
Do I need planning permission for an orangery?
Many orangeries fall under Permitted Development, provided they meet size and height limits. However, because orangeries have a solid roof and substantial brickwork, some local authorities treat them as extensions – always check with your planning department or specialist supplier.
Can I use a conservatory all year round?
Yes – modern conservatories with solar‑control glass, low‑E coatings, and thermally broken frames can be comfortable throughout the year. However, they have lower thermal mass than an orangery or brick extension, so temperature swings may be more noticeable.
Which adds most value to a home?
Industry surveys suggest an orangery typically adds 10–15% to property value, compared with 5–7% for a standard conservatory. Glass box extensions can add significant value for contemporary properties, but there is less published data.
What is the typical build time for each option?
Conservatories: 2–4 weeks. Orangeries: 6–12 weeks. Glass box extensions: 10–20 weeks, depending on complexity and structural engineering requirements.
Which option is most energy efficient?
Orangeries, with solid brick walls and a glass lantern, often provide the best thermal mass and insulation. However, a glass box extension specified with high-performance triple glazing and thermally broken frames can achieve excellent U-values, but it relies entirely on the glazing specification.
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