The project set out to create the highest quality office space in Wales, and energy efficiency was a key part of the plan. A key aim for the building was to achieve the coveted ‘Excellent’ rating under the Building Research Establishment Environmental Assessment Method (BREEAM).
The assessment takes into account a wide range of sustainability criteria, but energy performance is one of the most heavily weighted when a project is graded.
For Rio Architects, achieving a high level of natural light within the building was also extremely important. This meant specifying a high-performance glass that was not only energy-efficient, but also lacked any visible tinting.
Steve Berry, sales manager at Pilkington United Kingdom Limited, said: “To take advantage of its prime location, the Rio team wanted to maximise the 360-degree views of Cardiff by glazing the building floor to ceiling on all sides.
“The building is surrounded by 6,130m2 of glazed units, so the performance of the glass was absolutely critical to the project’s overall energy usage and the ease with which the interior can be climate-controlled.”
The challenge with entirely glazed buildings is to ensure that excess heating from sunlight doesn’t make the building too reliant on air conditioning during the summer, and that the glazing doesn’t allow too much energy to escape during the colder months.
In order to control the amount of energy coming into the building, a Pilkington Insulight™ Sun double glazed system was used.
The outer pane is Pilkington Suncool™ 66/33 T– a toughened glass that rejects 64 per cent of the sun’s energy while allowing twice as much daylight in. It also has the additional benefit of thermal insulation. The inner pane was Pilkington Optifloat™ – a high-quality standard float glass – and the two were separated by a 16mm argon-filled cavity to provide enhanced insulation.
The majority of the glazing was constructed as a curtain wall using architectural aluminium systems from American manufacturer Kawneer. However, for the double-height atrium, the Pilkington Planar™ structural glazing system was used, creating frameless glazed surfaces to maximise the sight-lines through the building and minimise its impact at street-level.
This met Rio’s design requirement for a high level of transparency along the public boulevard connecting Millennium Stadium to Cardiff's Central Station, which was an integral part of the original concept.
Open and inviting
Surrounding the atrium are 130m2 of double glazed units, held in place by low-profile stainless steel fixings and perpendicular glass fins, creating an uninterrupted wall of glass. The toughened fins are 19mm thick and ensure the glazing will stand up to high wind loads.
To prevent the risk of overheating as a result of excessive solar gain, again, Pilkington Suncool™ 66/33 T was used for the outer pane of the units.
Steve Berry added: “The structural glazed façade at ground level really enhances the sense of space both inside and outside the building, making it open and inviting despite its height.”
Tom Roberts, Senior Transactions Manager at Legal & General Investment Management Real Assets at Legal & General said: “One Central Square securing the BREEAM Excellent rating is an important achievement, and we see the sustainability of the scheme as a significant selling point.
“The glazing Pilkington has provided is not only one of the building’s defining features, but it has also allowed us to deliver on our energy performance targets.”
When complete, the wider Central Square scheme will also house a 14,000 sq m headquarters for BBC Wales.
Project: One Central Square, Cardiff
Building Owner: Legal & General
Architect: Rio Architects
Rio Architects’ client: Rightacres Property Co Ltd
Main contractor: Willmott Dixon
Curtain wall installer: Dudleys Aluminium
Structural glazing installer: Vitrine Systems