ETFE Roof: Northampton Bus Interchange

• Another concept realised with ETFE
• Low maintenance
• Beautifully designed

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Once the site of an abandoned fish market, the new £8m Northampton Bus Interchange was completed in 2013.

The highlight of the new station is the beautifully engineered ETFE roof which oversails the modern space.  Architen Landrell designed, manufactured and installed the double layer air filled ETFE system offering 1500m2 of coverage.  The cushion design is made up of triangles and rhomboids, adding interest to the complex roof design.

Why ETFE?

With all of the choices available for roofing materials today from metal to glass, ETFE was chosen because it is lightweight, bright, easy to install and economical.  ETFE cushions are 1% the weight of glass, providing cost savings for both steelwork and foundations.  ETFE is being used more and more in the transportation sector because it is bomb blast tested and approved.  Simultaneously, Architen Landrell is also installing an ETFE roof over the new East Croydon station.

Staying Dry:

Not only does the open air ETFE walkway canopy provide all weather protection for travellers in the station, it was designed tall enough to allow buses to drive underneath the ETFE overhangs. This protects passengers entering and exiting the buses from the elements.

Rainwater is managed through a series of gutters and hoppers installed throughout the vast ETFE roof. Hoppers channel water down the steel columns, underground and away from the site resulting in a clean, dry, open air station.

Light Control:

To keep the space cool on bright sunny days, we recommended Fritting. Fritting is a process whereby the ETFE foils are printed with a pattern. For Northampton, we recommended a dense 16mm silver dot frit (70% coverage), which reduces the light transmission of the double layer cushions from about 90% to about 63%. While the space is still light, bright and airy, the fritting is just enought to help with the solar glare and temperature.

Efficiency:

Because an ETFE foil cushion is a live system, it requires an Air handling Unit.  One unit will supply enough air to all of the linked cushions, maintaining a set pressure.  The system, engineered and manufactured by Architen, is extremely efficient. In fact, it only requires the power equivalent of running a 100 watt light bulb this is because pressure only needs to be maintained, not running all the time.

Challenges:

With this being a building site, the main challenge has been the coordination with other trades all of whom are working with limited access in and around various elements of construction.  To install the ETFE, Architen Landrell is using nets to create a safety barrier/platform for working at heights. This allows our installation engineers to work fast and safe.

Acknowledgements:

• Having recently completed the Bushey Academy with Kier Construction, we are pleased to be working together on another ETFE project.
• Thanks to D5 Architects LLP for their vision of using ETFE versus glass.
• BCAL Consulting: Engineering Firm
• Tensys:  Fabric Analysis