Thanks for getting in touch.
We'll get back to you shortly.
Need an urgent response?
Need an urgent response?
Situated in the heart of London’s Mayfair Conservation Area, Pegasus House and Nuffield House occupy one of the capital’s most architecturally sensitive and prestigious addresses. The redevelopment – designed by Trehearne Architects – sought to breathe new life into these characterful buildings while remaining entirely sympathetic to the heritage setting.
With the Piccadilly elevation forming part of a Grade II listed façade, maintaining the visual and architectural integrity of the retained frontages was not simply desirable – it was a fundamental requirement of the project.
Balancing heritage with modern performance
Working alongside Trehearne Architects, TRC Contracts was tasked with delivering a window solution that could satisfy some of the most demanding performance standards in the industry – all without compromising the historic character of the buildings’ retained façades. The scheme required bespoke timber sash and casement windows capable of meeting rigorous heritage, acoustic, thermal and solar control criteria across two distinct elevations: Piccadilly and Sackville Street. Adding further complexity, the project featured an extensive array of arched and circular window forms, requiring the kind of traditional craftsmanship that only an experienced specialist could reliably deliver within a live city-centre construction programme.
Key performance requirements
With the buildings’ future use spanning office, retail and residential occupancies in one of central London’s busiest and most noise-exposed locations, the performance specification was exceptionally exacting. Each window was required to achieve a thermal performance of Uw ≤ 1.1 W/m²K and an acoustic rating of at least Rw + Ctr 34 dB – essential for protecting occupants from the noise of Piccadilly.
Solar control was equally important, with a target g-value of no more than 36% and a visible light transmission of 69% specified to balance comfort with natural daylight. Where required, glass was specified as heat soak tested, and throughout, heritage-sensitive detailing and slim sightlines were non-negotiable.
Bespoke glazing engineered for two elevations
TRC developed a carefully considered glazing strategy that differed across the two elevations to meet each one’s specific demands.
On the Piccadilly elevation, where the Grade II listed façade dictated the use of slimmer cavity insulating glass units, TRC specified a high-performance triple-layer build-up: 4mm Sunguard 70/35 toughened, heat soak tested glass / 8mm krypton-filled cavity / 6.8mm acoustic laminate. This combination delivered an acoustic performance of Rw (C; Ctr) = 35 (-1; -4) dB, a centre pane U-value of 1.1 W/m²K, a solar factor of 35% and light transmission of 69% – meeting every target whilst preserving the visual character of the listed frontage.
On the Sackville Street elevation, a larger cavity unit was utilised to maximise both thermal and acoustic performance: 6.4mm laminated Sunguard Selekt 70 / 16mm argon-filled Multitech spacer / 6mm clear glass. The results were outstanding – an acoustic rating of Rw (C; Ctr) = 40 (-2; -6) dB and a centre pane U-value of 1.04 W/m²K, exceeding the original specification targets. Throughout both elevations, TRC maintained slim heritage sightlines and delivered the full range of bespoke sash, casement, arched and circular configurations required by the design – integrating advanced glazing performance within a window aesthetic that remains entirely true to the building’s original character.
Proof that heritage and performance go hand in hand
The completed redevelopment of Pegasus House and Nuffield House stands as a compelling demonstration of what can be achieved when traditional craftsmanship is combined with modern glazing science. The bespoke timber window package delivered full compliance with planning and heritage requirements, significantly improved acoustic comfort for future occupants, improved energy efficiency and solar control, and ensured long-term durability – all while preserving the architectural character that makes these Mayfair buildings so distinctive.
For TRC Contracts, this project is a proud example of our ability to navigate the most technically demanding, heritage-sensitive briefs and deliver results that satisfy architects, contractors and conservation officers alike.
