"Environmental concerns are at the heart of our union, and so it's right that our new head office sets the standard for green building in the 21st century," UNISON General Secretary, Dave Prentis.

The UNISON HQ was designed to the highest conceivable environmental standards, lowering the total carbon emissions for a development of this size by 53% (the GLA target was 20%), delivering carbon reductions in excess of 50% above Part L requirements, and achieving a BREEAM score of 73.53% rating Excellent. For a central London development it set the bar at a high sustainability standard, and is regarded as one of the greenest buildings in London.

Squire and Partners took a radical and holistic approach to fulfilling the brief - the entire building was designed and oriented to make it as energy efficient as possible. Rather than covering generating energy in an environmental way, the practice has produced a building that doesn't require a lot of energy in the first place. The philosophy has been to maximise use of natural light to minimise the need for artificial light, and to use the fabric of the building to respond to the climate, rather than needing a lot of energy to artificially control the temperature.

The atrium at UNISON takes advantage of its north/south orientation and the contours of the roof to naturally ventilate itself. Fresh, cool air is drawn into the building at basement level through a concrete plenum chamber. As the hot air rises in the atrium, cold air is drawn in to replace it. This stack effect is further enhanced by opening vents on the atrium roof, and prevailing south westerly winds which accelerate over the surface of the roof creating negative pressure, extracting the hot air.

In order to significantly reduce solar gains, highly efficient spectrally selective glazing was chosen. Furthermore, windows of the tower that face south are recessed into the façade providing additional shading. On the north side of the tower, the windows can maximise the daylight coming into the building without the need for shading as the sun never directly hits the façade.

Each of the office floors has a very efficient Variable Refrigerant Flow (VRF) comfort cooling and heating system with floor by floor fresh air ventilation. All ventilation plants have been provided with heat recovery. The floor by floor configuration reduces fan power and the VRF system enables 'waste heat' from 'cooling zones' to be reused to heat other areas of the building.

The building has been designed to make the best use of natural light, thereby reducing the need for artificial lighting. All lights are able to be controlled by infrared sensors and are fully dimmable when the space has sufficiently daylight. Outside of normal office hours, if no movement is detected, the lights will start to switch off.

The original design included two biomass boilers to provide heating and hot water on the site, which burn to the utmost efficiency, fuelled with carbon neutral pellets made from recycled wood. The biomass boilers would ensure that 20% of energy for the new building is from renewable sources.

After building work commenced, Camden Council identified local organisations including UNISON, to share the use of a Combined Heat & Power Plant to be built on a neighbouring estate. The UNISON Centre has been designed so that its core heating source can be linked into the proposed local CHP when it becomes available. This would represent even further efficiencies and energy cost reductions in the future.

A significant amount of solar photovoltaic panels have been incorporated into the new façade and the energy created will be viewable on a live meter which records the gain. This should generate nearly 2,000 of electricity for the building each year. UNISON has a policy of using 100% recycled electricity in all of its building where possible.

Three roofs are "green roofs" planted with sedum, a succulent plant with yellow or pink coloured flowers. Green roofs increase biodiversity, reduce the amount of carbon dioxide in the atmosphere, and also produce oxygen to improve the air quality. They also provide greater thermal performance and roof insulation, reducing heat in summer and heat loss in winter.

The fifth floor roof area is decked and landscaped with raised planters and small trees/hedges to enrich the ecology of the site while providing an external social space for UNISON members and visitors. The building roofs are used to collect rainwater, which is then used for UNISON's non-drinking needs (eg, flushing toilets), thereby reducing the overall consumption of water by about 20%.