Al Bahr Towers, Abu Dhabi

The Al Bahr office development in the financial centre of Abu Dhabi comprises two near-identical, 26-storey, 145m-tall towers with striking Islamic geometric patterning. Sustainability and solar control were important drivers of the design.

'From the outset of the project it was acknowledged that two elements would be key to creating an innovative and sustainable building: heat and light,' says Arfon Davies, associate director at Arup.

'By carefully balancing these it was determined that significant reductions in energy consumption due to cooling and electric lighting could be achieved.'

The starting point was to examine approaches to facade design, specifically how daylight and heat could be controlled within high-rise buildings in the Middle East. Most use highly glazed facades with dark, reflective, or body-tinted, glass. 'This curtain-walling type of solution limits solar gain, but significantly reduces daylight and general internal comfort,' says Davies.

Fixed shading elements were considered, but while they provided improved daylight availability and glare control, the client's brief asked for something 'iconic and innovative'. The consensus was that some form of dynamic system was needed, responding to daylight availability and sun position.

The traditional Islamic mashrabiya screened window was the inspiration for heat and glare control for the twin Al Bahr towers in Abu Dhabi, cladding all but their north-facing sides

'The dynamic system, and the geometry of the associated shading system, was also a perfect way to embrace the mashrabiya within the project,' says Davies.

Used extensively throughout the region and part of the vernacular of traditional Arabic architecture, the mashrabiya is a projecting oriel window that provides shade and visual comfort for building occupants. Characterised by an intricate lattice work screen - typically made of either wood or stone - it provides a view of and connection to the outside while offering protection from heat and glare. The mashribaya concept had appeared during the course of the extensive cultural research the team had felt was essential before starting the design process.

Developed specially for Al Bahr, the shape of this contemporary version was derived directly from historical references to the original Islamic shading device, as well as detailed studies that assessed all possible sun positions at the site location. This was used in conjunction with high-performance facade glazing and motorised interior blinds, to allow occupants more individual control.

The mashrabiya, made from a woven PTFE fabric, each weigh 1.5 tonnes and are motorized

Each tower has 1,049 mashrabiyas cladding the east, south and west facades, forming an adaptable skin. Made from a woven PTFE fabric, they each weigh around 1.5 tonnes. Part of a unitised system, each cantilevers 2.8m from the primary structure, while the supporting arms allow connection from the ends of six adjoining mashrabiya. The motor at the centre of each one moves outwards to open the shading device, and inwards to close the shading device. Grouped in sectors, they are controlled by sun-tracking software, with the control system linked to an anemometer at the top of the building.

Climate-based daylight modelling was used to assess performance, together with useful daylight index (UDI) calculations.

'A detailed assessment of the combined shading and glass performances meant that a correct balance between solar control and light penetration was achieved,' says Davies. 'The type of glass selected has a clear appearance, with high visible light transmittance enhancing the daylighting and the view through, while the external shading panels help reduce the solar radiation significantly -- and only where and when needed.'

Project Info

Architect: Aedas Architects
Owner/developer: Abu Dhabi Investment Council
Structural engineer and MEP: Arup
Project manager: Mace
Contractor: Al-Futtaim Carillion