A sunroom — sometimes called a garden room, garden office, or glazed extension — is a highly glazed structure designed to bring light and connection with the garden into the home. Unlike a conventional extension, a sunroom typically features floor-to-ceiling glazing on one or more walls, a glazed or part-glazed roof, and is designed to feel open to the outside.
In 2026, a properly built sunroom costs £20,000–£50,000 installed on a standard 15–20 m² footprint. Budget options using prefabricated uPVC frames exist from £10,000, but these sacrifice thermal performance and longevity.
Sunroom vs. Conservatory vs. Extension
These three terms overlap considerably in the UK market. The key practical differences:
| Feature | Conservatory | Sunroom | Extension |
|---|---|---|---|
| Roof type | 75%+ glass/polycarbonate | Solid or part-glass | Solid (tiled/flat) |
| Thermal performance | Poor to moderate | Moderate to good | Good to excellent |
| Year-round use | Difficult without upgrades | Yes (if insulated) | Yes |
| Building Regs (England) | Often exempt (if glazed) | Usually required | Always required |
| Planning (PD) | Usually PD | Usually PD if ≤30 m² | Subject to PD limits |
| Cost (15–20 m²) | £8,000–£25,000 | £15,000–£50,000 | £30,000–£65,000 |
A sunroom occupies the middle ground: better than a conservatory thermally, less expensive and more light-filled than a traditional extension.
Sunroom Types and Costs
Prefabricated uPVC or Aluminium Sunroom Kit
Manufacturer-supplied frame kits with pre-engineered glazing and roof sections. Installers assemble on a prepared concrete base. Thermal performance is limited compared to a bespoke build.
- Supply cost (system): £5,000–£12,000
- Installation labour: £2,000–£4,500
- Concrete base: £1,500–£3,000
- Total installed: £8,500–£19,500
Timber Frame Sunroom
Structurally independent timber frame with aluminium or timber glazing and a flat or pitched roof with glazed panels. Better thermal performance; more design flexibility; requires more skilled labour.
- Structural timber frame: £4,000–£8,000
- Aluminium glazing system: £5,000–£12,000
- Glazed roof section: £3,000–£8,000
- Concrete base and connections: £2,000–£4,000
- First fix (electrics, plumbing, heating): £2,000–£5,000
- Internal fit-out: £2,000–£6,000
- Total: £18,000–£43,000
Bespoke Aluminium / Steel Frame Sunroom
Architect-specified bespoke system with thermally broken aluminium frames, triple glazing, and a structural glass or aluminium-and-glass roof. Highest performance and most design freedom.
- Bespoke frame and glazing (system supply): £15,000–£40,000
- Installation: £5,000–£12,000
- Base, connections, services: £4,000–£8,000
- Internal fit-out: £3,000–£10,000
- Total: £27,000–£70,000+
Cost Breakdown Table (Timber Sunroom, 4 m × 4 m)
| Element | Low | High |
|---|---|---|
| Structural engineer | £500 | £900 |
| Concrete slab (150 mm reinforced) | £1,800 | £3,500 |
| Timber structural frame | £3,500 | £6,500 |
| Aluminium glazing (3 walls) | £4,000 | £9,000 |
| Glazed roof system (aluminium + glass) | £3,500 | £8,000 |
| External door (bifold or sliding) | £2,000 | £5,000 |
| Electrics (circuit, lighting, sockets) | £700 | £1,800 |
| Underfloor heating (electric mat) | £600 | £1,400 |
| Internal finish (floor, ceiling, decoration) | £1,500 | £4,000 |
| Total | £18,100 | £40,100 |
Glazing Specification
The glazing is where the most meaningful trade-offs occur:
| Glazing Type | Centre-of-Pane U-value | Typical Cost (per m²) | Notes |
|---|---|---|---|
| Double glazed (Ar, low-E) | ~1.0 W/m²K | £80–£160 | Standard; most sunrooms |
| Triple glazed | ~0.6 W/m²K | £140–£250 | Better for north-facing rooms |
| Solar control glass | ~1.0–1.4 W/m²K | £100–£200 | Reduces heat gain; key for south-facing |
| Structural glass roof | ~1.0–2.0 W/m²K | £200–£500 | Prestige; condensation risk if not thermally broken |
For a south-facing sunroom, solar control glass on the roof and south elevation is strongly recommended — without it, temperatures can exceed 40°C in summer.
Planning Permission and Building Regulations
Planning permission — a sunroom built as a rear extension on a dwelling house is typically permitted development in England if:
- Single storey and under 4 m in height
- Rear projection no greater than 4 m (detached) or 3 m (semi/terrace)
- Not exceeding 50% of original garden coverage in total (with all outbuildings)
- Not forward of the principal elevation
Building Regulations — unlike a traditional conservatory with more than 75% glazing, many sunrooms (particularly those with solid or only partially glazed roofs) are not exempt from Part L requirements. If the structure is thermally separated from the main house by an external-standard door and window, the exemption may apply. If the sunroom is open-plan with the house (no separating door), it is treated as a habitable room and must meet full Part L targets — wall U ≤0.18, roof U ≤0.13.
Always confirm with your local authority building control before starting.
Getting the Best from a Sunroom
- Specify thermally broken frames — aluminium frames with a polyamide thermal break significantly reduce condensation on frames in winter.
- Include mechanical ventilation — glazed spaces build up heat fast; ridge vents, opening rooflights, or a through-wall fan are essential.
- Don’t underestimate the foundation — a well-engineered concrete slab with edge beam and DPM is more reliable than a timber deck or paving slabs.
- Use a specialist — sunroom and glazed extension specialists typically offer a manufacturer-backed system warranty (10 years on frames, 5 years on seals) that generalist builders cannot match.
