Guide figures, before you've told us anything.
Real ranges by extension type, a full worked breakdown of a typical glass extension, and exactly what's excluded — so you can compare us honestly against anyone else quoting.
| Type | Range | Typical | On site |
|---|---|---|---|
| Single-storey rear, standard glazing | £140,000–£220,000 | £175,000 | 12–16 weeks |
| Glass box, frameless roof lantern | £220,000–£340,000 | £280,000 | 16–24 weeks |
| Orangery, traditional lantern roof | £240,000–£380,000 | £300,000 | 18–26 weeks |
| Wrap-around, side and rear combined | £320,000–£480,000 | £390,000 | 22–30 weeks |
| Two-storey extension | £380,000–£560,000 | £450,000 | 26–34 weeks |
Guide ranges for Oxfordshire and the Cotswolds. Sources: RIBA's build cost guide (updated 2026) and industry data from the Federation of Master Builders. Prices vary by region and specification — bespoke steel glazing and joinery sit well above standard-build costs by design. Every figure is confirmed in writing after a consultation — none of this is a quotation.
Extension types explained
Single-storey rear
The most common project — a kitchen and dining extension across the back of the house, with standard glazing and a flat or pitched roof.
Glass box, frameless roof lantern
Structural steel frame with minimal-sightline glazing and a frameless roof lantern — the signature Aldermere look.
Orangery
A traditional lantern-roofed structure, often the right answer on a listed or conservation-area house where full glazing wouldn't be approved.
Wrap-around
Side-return and rear combined into one continuous space — usually the biggest single change to how a house is lived in.
52m² glass box extension, Oxfordshire, frameless roof lantern, bespoke kitchen
- Groundworks & foundations£38,000Excavation, footings, drainage and services diversion
- Structural steel frame£46,000Design, supply and fit, sized by the structural engineer
- Bespoke glazing & roof lantern£72,000Frameless steel-look glazing system, fabricated to the opening
- Roof, walls & external finishes£31,000Render, stone facing to match the existing house, guttering
- First & second fix£38,000Electrics, plumbing, underfloor heating, insulation, plastering
- Bespoke kitchen & joinery£42,000Designed and built in-house for this room specifically
- Flooring, decoration & snagging£13,000Final finish and the walkthrough before sign-off
Included, excluded, and priced.
Included
- Concept & detailed architectural design✓
- Structural engineering & planning application✓
- Scaffold, welfare, site management✓
- Full decoration to a finished standard✓
Excluded (priced separately)
- Landscaping & external terracingfrom £18,000
- Bespoke furniture beyond fitted joineryfrom £6,000
- Whole-house heating upgrade, if requiredfrom £14,000
- Listed building consent application feesfrom £2,500