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A modern glass box extension has been built onto this 18th century London home to create a light and airy living space. By adding a glass box extension, which features slim framed sliding glass doors and a structural glass roof, the history-rich property has received a modern touch which allows for floods of natural light.

The light-filled extension also contrasts with the dark, atmospheric interior scheme across the remaining ground floor. Biophilic design elements, including large plants and green finishes, strengthen the relationship between the internal living space and garden.

Products Used

Project Partners

Architect: MW Architects

Photography: French+Tye Photography

Location

London

Glass box extension in London contrasting old and new

The central design challenge was to introduce a light-filled contemporary living space without diluting the architectural character of the original 18th-century house.

Rather than replicating the existing building, the extension was designed as a transparent glass volume. Frameless structural glass walls and slim sliding doors reduce the visual weight of the addition, allowing the white exterior of the historic property to remain clearly visible behind the contemporary glazing.

This contrast continues internally. The bright kitchen and family space provides a deliberate transition from the darker, more enclosed ground-floor interiors, while planting and green finishes reinforce the connection between the extension and garden.

The glass box extension in London therefore acts as both a functional new living space and an architectural transition between the historic home and its external setting.

Slim sliding doors for a flush garden connection

Slim framed sliding glass doors form the principal opening between the extension and garden. The 21mm interlocks minimise visible aluminium within the glazed elevation, allowing daylight and external views to remain uninterrupted when the doors are closed.

A flush threshold creates a level transition between the family space and garden. When opened, the sliding doors extend the usable living area outdoors without introducing folding panels or visually heavy framing within the opening.

The sliding system was coordinated with the adjoining structural glass walls so the opening and fixed glazing read as one controlled composition.

Structural glass roof above the window seat

A structural glass roof was integrated above the window seating area to introduce daylight from overhead. This allows natural light to reach deeper into the extension while creating a direct visual relationship with the sky and garden.

The supporting profiles are concealed within the surrounding building finishes, maintaining the frameless character of the roof glazing.

The structural glass roof connects with the adjoining glass walls to create a continuous glazed envelope around the seating area, reinforcing the architectural identity of the extension.

Performance considerations

Performance detailing focused on maintaining a comfortable internal environment despite the extensive use of glass across the walls and roof.

The structural glazing uses thermally broken fixing details and insulated glass units to reduce heat loss through the building envelope. Solar control coatings were incorporated within the roof glazing to limit overheating and help regulate internal temperatures while maintaining daylight transmission.

Thermally broken aluminium framing supports the performance of the sliding doors without compromising their minimal appearance. The flush threshold and glass-to-building interfaces were also coordinated to preserve weather resistance across the opening.

Together, these measures allow the glass box extension in London to maintain a minimal glazed appearance while providing the thermal and solar performance required for year-round family living.

Technical details

Slim framed sliding doors: 21mm sightline; max tested sliding pane 8.5m², up to 4m high and 500kg; glass thickness 26–32mm; typical Ug 1.0 W/m²K; typical Uw >1.1 W/m²K; Air Class 4 / Driving Rain Class 7A / Wind Class C4/B5; sound insulation up to 39dB; PAS 24 security; flush threshold connecting the family space with the garden
Frameless structural glass walls: thermally broken fixing system; 63mm profile depth; max glass thickness 41.5mm; expected Uw 1.1 W/m²K; minimum fixing setback 55mm; 60mm profile height; supporting structure limited to 5mm maximum deflection
Structural glass roof: glass thickness up to 37.5mm; expected Uw 1.2 W/m²K; 95mm profile height; minimum 150mm upstand; solar control coating incorporated to help manage overheating
Glass box configuration: structural glass walls, roof glazing and slim sliding doors coordinated to form a transparent kitchen and family extension

Architectural glazing for historic London homes

White House demonstrates how a transparent glazed extension can introduce daylight and garden access while remaining clearly distinguishable from the architecture of a historic home.

This approach is suited to architects and specifiers working on period properties where structural glass walls, roof glazing, slim sliding doors and solar control must be coordinated as one architectural package.

Planning a similar glass box extension in London? Contact IQ Glass for technical advice on frameless structural glazing, sliding door configurations, glass roofs and performance-led detailing for historic homes.