Hallam Street

Rooftop Extension in London Featuring Slim Framed Sliding Glazing

Hallam Street sits within the Harley Street Conservation Area, an address known for its historic significance and architectural refinement. At 26–28 Hallam Street, an eight‑storey commercial building with a 1940s exterior was converted into six luxury residential flats for The Howard de Walden Estate. As part of this transformation, a new penthouse level was added to create an exclusive rooftop extension in London with panoramic views across the city. IQ Glass was appointed to design and install the specialist glazing for this elevated living space, providing a slim framed sliding system that wrapped around the new extension in a U shaped configuration.  

The rooftop extension forms the centrepiece of the redevelopment and was designed to combine contemporary detailing with a respectful nod to the building’s mid‑century architectural character.

Products Used

Location

London, UK
Sliding doors to rooftop extension in London - IQ Glass - Hallam Street
Sliding doors to rooftop extension in London - IQ Glass - Hallam Street
Sliding doors to rooftop extension in London - IQ Glass - Hallam Street
Sliding doors to rooftop extension in London - IQ Glass - Hallam Street

Integrating Modern Glazing Into a Conservation Area 

The building’s conversion introduced several architectural challenges. The rooftop extension needed to deliver a modern, light filled residential environment without disrupting the building’s 1940s identity or the wider heritage context of the Harley Street Conservation Area. The design team, comprising Holt Architecture and Sonnemann Toon Architects, were tasked with creating a living space that maximised views while retaining subtle references to the original building’s Art Deco detailing.  

The depth of the former commercial floorplate meant that natural light was limited towards the centre of the new penthouse. Creating openings that could deliver daylight into the stairwell and down through several floors was critical. The rooftop terrace also required direct step free access and glazed elevations that could frame views across London without adding visual weight to the façade.

U Shaped Sliding Façade for Maximum Transparency 

To meet the brief for clarity, lightness and uninterrupted views, IQ Glass installed a slim framed sliding door system that formed the primary west‑facing elevation of the rooftop extension and continued around two adjoining elevations. The front elevation included a bi‑parting configuration measuring 7.2 metres in width and 2.2 metres in height, with two central sliding panels opening over fixed sidelights. This arrangement provides panoramic views and creates a wide, uninterrupted opening onto the roof terrace.  

Two fixed returns were connected to the main elevation at 90 degree corners, measuring 1170 mm by 2200 mm and 800 mm by 2200 mm respectively. These returns complete the U shaped glazed wrapping, enhancing the architectural rhythm of the rooftop structure while maintaining the minimalist aesthetic. The slim 21 millimetre sightlines contribute to a sense of openness and ensure the glazing reads as a lightweight addition to the historic building.

Daylighting the Stairwell With Structural Rooflights 

Because natural light needed to penetrate deeper into the penthouse and down the circulation spaces, IQ Glass supplied a frameless strip rooflight and a small, fixed casement window positioned above the staircase. These elements deliver daylight into the centre of the plan and allow it to cascade into the lower levels. The frameless design ensures the rooflight reads as a clean architectural incision rather than an object on the roof.  

Frameless glass balustrades were then installed around the stairwell to preserve the flow of light and maintain the minimalist aesthetic. This detail ensures that the structural glazing works holistically within the extension and supports the aim of creating a bright and modern rooftop retreat that remains visually connected to the rest of the residence.

Sliding doors to rooftop extension in London - IQ Glass - Hallam Street
Sliding doors to rooftop extension in London - IQ Glass - Hallam Street
Sliding doors to rooftop extension in London - IQ Glass - Hallam Street
Sliding doors to rooftop extension in London - IQ Glass - Hallam Street

Project Significance 

Hallam Street has a rich architectural history. Originally laid out in the eighteenth century, the street evolved significantly during the late nineteenth and early twentieth centuries, culminating in the 1940s commercial building that became the focus of this redevelopment.  

The rooftop extension forms a key part of the 2012 conversion project valued at £1.9 million. It not only added premium residential accommodation but also opened views over the conservation area, contributing to the long-term desirability of the property. The carefully curated palette of materials draws from the building’s mid‑century origins, combining traditional ironmongery and joinery references with contemporary glazing. This creates a balanced architectural expression that appeals to UHNW individuals seeking distinctive living spaces within central London.

Technical details

  • U shaped slim framed sliding door system made from thermally broken aluminium with 21mm sightlines.  
  • Front elevation: 7.2 m by 2.2 m bi‑parting configuration 
  • Two fixed return panels: 1170 mm by 2200 mm and 800 mm by 2200 mm 
  • Frameless strip rooflight over staircase 
  • Small fixed casement window 
  • Frameless glass balustrades for stairwell

Creating a Rooftop Extension in London 

For architects, developers and clients exploring opportunities for a rooftop extension in London, this project demonstrates how slim framed glazing and structural rooflights can elevate the quality of urban living spaces. The Hallam Street penthouse illustrates the value of designing with transparency, daylight and minimalism at height, particularly within conservation settings where sensitivity and precision are essential. 

If you are planning a rooftop extension or require specialist guidance on glazing solutions for complex central London developments, IQ Glass can provide feasibility assessments, technical advice and fully bespoke glazing systems. Contact our team to discuss your project. 

Associated Products

luxury new build home with minimal glass facade

Slim Framed Sliding Glass Doors

Sliding doors with ultra-slim sightlines, offering only the highest levels of performance and durability.
Frameless Windows at Claywood by IQ Glass

Frameless Windows

Frameless picture windows are the perfect solution for achieving a minimalist design that maximises visibility

Strip Rooflights

Strip Rooflight

Using structural glass to create long runs of glass, connected together with silicone joints.

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