The 122 Leadenhall Street tower – widely known as the Cheesegrater – remains one of the City of London's most recognisable office landmarks. Guardian Glass UK features the project as a reference case on its website, highlighting the glazing specification that wraps the 225-metre-tall structure. For façade engineers, window fabricators and building consultants, the project offers insight into how high-performance glass contributes to thermal efficiency, occupant comfort and compliance with UK building regulations in a high-rise commercial environment.
Project Context: A Skewed Wedge in the City's Financial Core
Completed and occupied in 2014, 122 Leadenhall Street stands 225 metres tall and contains 46 storeys of Grade A office space. Its distinctive wedge-shaped profile – which gave rise to the Cheesegrater nickname – was designed to preserve sight lines of St Paul's Cathedral from Fleet Street, a protected view corridor under London planning policy. The tower's sloped southern façade and near-vertical northern wall create a large, continuously glazed envelope that must balance daylight admission, solar heat gain control and thermal insulation.
Guardian Glass UK supplied the project with a specified solar-control glazing system designed to meet the thermal and optical performance targets set by the design team. The building's all-glass curtain wall relies on the glass package – rather than external shading devices – to manage solar heat gain, making the choice of coating and insulating glass unit (IGU) configuration critical to both energy performance and mechanical plant sizing.
Glass Specification: Solar Control and U-Value Requirements
The façade employs a double-glazed IGU with a low-emissivity coating on the inner pane surface facing the cavity. This configuration, typical for commercial high-rise developments, delivers a centre-pane U-value (thermal transmittance) of approximately 1.1 W/m²K, in line with UK Building Regulations Part L standards for non-residential buildings at the time of completion. The gas fill – typically argon – further reduces conductive heat loss across the cavity.
Solar control is provided by a selective coating that reflects a significant portion of near-infrared radiation while maintaining visible light transmittance above 50 per cent. This balance is crucial for deep-plan office floors, where natural daylight penetration reduces artificial lighting demand and supports occupant well-being. Guardian Glass UK's SN (SuperNeutral) and ClimaGuard product families are commonly specified for such applications, offering g-values (solar factor) in the range of 0.25 to 0.35, which limits peak cooling loads during summer months.
Thermal Bridge Management and Frame Integration
The Cheesegrater's unitised curtain wall system integrates aluminium framing with thermal breaks to minimise heat transfer at the perimeter of each IGU. The glass edge is sealed with a warm-edge spacer bar, reducing the risk of condensation and improving the overall frame U-value. For projects of this scale – the building contains more than 28,000 square metres of glazing – consistent thermal performance across thousands of units is essential to meet whole-building energy models submitted for compliance and BREEAM certification.
Guardian Glass UK's role extended beyond glass supply to include technical consultation during the design phase, ensuring that the specified product met structural, acoustic and fire safety requirements in addition to thermal targets. This level of integration is increasingly expected by main contractors and façade subcontractors on complex projects, where coordination between cladding, mechanical systems and structural steel is tightly sequenced.
Compliance with UK Building Regulations and Energy Performance
At the time of the Cheesegrater's completion, Part L 2013 of the Building Regulations set a limiting fabric parameter for glazing in non-domestic buildings, with centre-pane U-values typically not exceeding 1.2 W/m²K for standard façade systems. The project achieved a notional carbon performance that qualified it for a BREEAM 'Excellent' rating, in part due to the low solar gain and reduced cooling demand enabled by the solar-control IGU.
Under the 2021 update to Part L – now in force for all new non-residential projects – the centre-pane U-value threshold has tightened further, with many designers targeting 1.0 W/m²K or lower. Guardian Glass UK's current portfolio includes triple-glazed units and advanced low-emissivity coatings that deliver U-values as low as 0.5 W/m²K, suitable for Passivhaus-standard office buildings and retrofits where fabric performance is prioritised over mechanical conditioning.
Broader Context: High-Performance Glass in UK Commercial Construction
The Cheesegrater project exemplifies a wider trend in UK commercial real estate: the use of high-performance solar-control glazing to achieve energy efficiency in fully glazed envelopes. Other major London towers, including the Leadenhall Building (known as the Walkie-Talkie) and 22 Bishopsgate, employ similar strategies, specifying advanced coatings from suppliers such as Guardian Glass, Pilkington UK and Saint-Gobain.
For UK fabricators and installers, understanding the performance characteristics of these products is increasingly important. Clients and consultants now routinely request g-value, light-to-solar-gain (LSG) ratio and whole-window U-value calculations during tender, and product data sheets must align with BFRC (British Fenestration Rating Council) and EN 673/EN 410 test standards. Guardian Glass UK publishes detailed technical data for each coating system, enabling accurate input into thermal modelling software such as IES-VE and DesignBuilder.
Implications for Fabricators and Contractors
Projects on the scale of the Cheesegrater require fabrication tolerances and quality control procedures that go beyond typical residential or low-rise commercial work. Each IGU must meet dimensional accuracy within ±1 mm, and coatings must be inspected for defects or scratches prior to assembly. Guardian Glass UK operates production facilities that supply pre-cut, coated glass to processor partners, who then assemble the IGUs and deliver finished units to the curtain wall contractor.
For curtain wall installers, the logistics of handling 28,000 square metres of unitised panels – each weighing several hundred kilograms – demand careful site coordination, crane access and weather-dependent sequencing. The use of high-performance glass with specific handling requirements (e.g. low-emissivity coatings that must not be scratched) adds a layer of risk management and quality assurance that is reflected in contract pricing and insurance provisions.
Future Outlook: Tighter Standards and Retrofit Demand
Looking ahead, the UK government's commitment to net-zero carbon by 2050 is driving further tightening of fabric performance standards. The Future Buildings Standard, expected to be introduced in 2025–2026, will likely mandate whole-building operational carbon assessments and push centre-pane U-values below 1.0 W/m²K for all non-residential projects. Façade systems that can demonstrate both low embodied carbon (through recycled glass content and local sourcing) and superior operational performance will gain competitive advantage.
Guardian Glass UK and other suppliers are also preparing for increased demand in the retrofit market, where older office towers with single-glazed or thermally inefficient curtain walls require overcladding or full façade replacement. Projects such as the Cheesegrater serve as case studies for the performance gains achievable through modern glazing systems, and provide a benchmark for specifiers evaluating upgrade options on existing stock.
The Cheesegrater remains a high-profile demonstration of how advanced glass processing and façade engineering can deliver both architectural ambition and regulatory compliance. For UK fabricators, installers and consultants, the project offers a practical reference point for understanding the technical and commercial requirements of high-performance glazing in demanding commercial applications.
