What is a glazed extension?
A glazed or contemporary extension uses large panes of glass, slim aluminium frames and modern cladding to create a bright room that contrasts with the original house. Frameless corners, structural glass roofs and minimal sliding doors are typical features.
Large areas of glass need careful design to meet building regulations for energy use and overheating. We work with the engineer and glazing supplier so the structure and glazing are designed together.
What we handle
- Contemporary design and planning drawings
- Structural design for steel frames and glass supports
- Energy and overheating calculations where needed
- Foundations, walls and insulated roof
- Large-format sliding doors and fixed glazing
- Cladding or render finish
- Electrics, heating and finishes
- Building control sign-off
Options to consider
Frameless glass corner
A corner with no visible post, supported by a concealed steel frame.
Structural glass roof
A walk-on or sloping glass roof for maximum light.
Composite or timber cladding
Durable cladding that contrasts with brickwork.
Minimal sliding doors
Large panels with slim sightlines.
How much does a glazed extension cost?
A glazed extension typically costs £2,800–£4,200 per m² of floor area across the UK, including VAT at 20% (standard rate). A typical 18 m² project comes to roughly £50,500–£75,500. Build time is usually 12 to 16 weeks on site; glazing lead times can be 6 to 10 weeks. Design, structural calculations and council fees are extra.
| Region | Guide range (per m² of floor area) |
|---|---|
| London | £3,650–£5,450 |
| South East | £3,150–£4,700 |
| East of England | £2,950–£4,450 |
| South West | £2,850–£4,300 |
| West Midlands | £2,700–£4,050 |
| East Midlands | £2,650–£4,000 |
| North West | £2,650–£3,950 |
| Yorkshire and the Humber | £2,600–£3,900 |
| North East | £2,500–£3,800 |
| Wales | £2,600–£3,850 |
| Scotland | £2,700–£4,050 |
| Northern Ireland | £2,400–£3,600 |
What changes the price:
- Glazing size, specification and lead time
- Steel framing
- Cladding material
- Overheating and energy design
- Lighting and finishes
- Access for large glass panels
Use the guide price tool for a figure based on your measurements, or see all guide prices.
Do I need planning permission?
England
In England a single-storey rear extension is often permitted development: broadly up to 3 metres deep on a semi-detached or terraced house and 4 metres on a detached house, no higher than 4 metres, with eaves no higher than 3 metres within 2 metres of a boundary, and covering no more than half the garden. The larger home extension scheme allows up to 6 or 8 metres if you notify the council first and neighbours have a chance to comment. In conservation areas, National Parks and National Landscapes the larger home extension route, side extensions and cladding are not permitted development. Flats and houses whose rights have been removed need a planning application, and listed buildings need listed building consent.
Wales
In Wales a single-storey rear extension is often permitted development: up to 4 metres beyond the rear wall and up to 4 metres high, with eaves no higher than 3 metres within 2 metres of a boundary and no more than half the land around the original house covered. Wales has no larger home extension prior approval route, so deeper extensions need a planning application, as do extensions to flats, listed buildings and houses whose rights have been removed.
Scotland
In Scotland a single-storey extension is often permitted development (Class 1A): where any part is within 1 metre of a boundary, it can project up to 3 metres from the rear wall of a terraced house or 4 metres on other houses, with eaves no higher than 3 metres, an overall height of 4 metres and no more than half the front or rear garden covered. The rights do not apply in conservation areas or to flats, and a building warrant will usually still be needed before work starts.
Northern Ireland
In Northern Ireland the Planning (General Permitted Development) Order (Northern Ireland) 2015 allows single-storey rear extensions of up to 3 metres on attached houses and 4 metres on detached houses, no higher than 4 metres, with eaves no higher than 3 metres within 2 metres of a boundary. Houses with removed rights need planning permission, listed buildings need consent, and in conservation areas extensions must stay single-storey and must not come forward of the front or side walls.
Even when planning permission is not needed, building regulations approval (a building warrant in Scotland) usually is. We make the applications and book the inspections.
How long does it take?
Typically 12 to 16 weeks on site; glazing lead times can be 6 to 10 weeks. Surveys, design and approvals usually take 3 to 4 months beforehand.
How it works
- 01
Free visit
We look at the property, discuss what you want and measure up.
- 02
Design and fixed quote
Drawings, calculations and an itemised price for the agreed specification.
- 03
Approvals
Planning or permitted development, building regulations and neighbour matters.
- 04
Build and sign-off
Built to a written programme, with a completion certificate at the end.
Glazed and contemporary extensions: questions and answers
Will a glass extension be too hot in summer?
It can be if poorly designed. Solar-control glass, roof overhangs and opening vents reduce overheating, and building regulations may require calculations to show the design works.
Does it need planning permission?
The same rules as other extensions apply, but contemporary designs in conservation areas are assessed carefully. We discuss the design approach with you before applying.
How long do large glass panels take to arrive?
Often 6 to 10 weeks after final measurements, so we order them as soon as the structure is built.
Is triple glazing necessary?
Not always. High-performance double glazing can meet the standards; triple glazing helps in exposed locations.
Can large glass panels be lifted in?
Some need a crane or glass-lifting robot. We plan access during design.
Is VAT charged?
Yes, VAT at the standard 20% rate applies to extensions. Our guide prices include it.