eliminating the need for manual cleaning. Saint-
Gobain claims the membrane also reduces surface roof
temperatures and decreases heat absorption, lowering
air-conditioning requirements.
“We have two parts that make up the moveable
square in the middle. They open and come down,
exposing the roof. These are made of a plastic clad
material, and this stays clean,” says Woodrow.
“The rest of the roof, though, the fixed part, this
is PVC and this does need to be cleaned,” he admits.
“We have to fasten up in harnesses twice a year and
give it an inspection. We look for damage, which isn’t
hard to repair, you just use a hot iron. We also look
for debris. To clean it you just use soap and water and
a mop,” he says.
While the cleaning of the AT&T is a surprisingly
simple process, for other venues it can take some
inventive thinking. Prior to the 2019 Cricket World
Cup in England, the Kia Oval, which was one of the
tournament’s venues underwent a spring clean of its
grandstand roofing canopy. However, using machinery
to allow workers to perform the job was not an option
as it was deemed too heavy to have on the field and
costs too high. The solution was to deploy a team of
trained abseil technicians to gain access to all the
structural steels and roofing sheets, where they would
use a pressurized steam cleaner to clean over 53,000ft2
(5,000m2) of surfaces. The job took over 300 hours
to complete, with over 1km of rope needed to support
the team working at heights of up to 82ft (25m) to
restore the grandstand.
The trade off
When it comes to having retractable roof venues there
are going to be a number of energy and operational
cost implications.
“Once you decide to close the building there is a
huge demand on the AC, but also you have the ‘stack
effect’, where warm air gets trapped up at the top,” says
Mohit Mehta, principal and building performance
director at ME Engineering.
While translucent PTFE and ETFE materials
provide the players and fans an outdoor experience
while still being protected, this comes at a price.
“All this sun that is coming in is providing a lot
of heat. These materials are making the stadium
a giant solarium,” says Mehta.
CABLE GUIDE
In Germany, Bundesliga soccer club Eintracht Frankfurt’s
Waldstadion (commercially named the Commerzbank Arena)
became one of the first soccer stadia in Europe with a retractable roof.
A 96,875ft² (9,000m²) section of the membrane roof is retractable
and is operated by a drive system supplied by Austria-based Eccon.
The roof is built using a steel cable construction with the flexible
membrane roof winched open and closed by the cable drive system
along the tensioned steel cables, which provides an opening or
closing time within 15 to 20 minutes.
Veronika Rothweiler, architect and business manager at Eccon
explains how the drive system is easy to maintain as the cable drive
system is not prone to dust and dirt and the wear is low.
“For maintenance it makes sense to check the system twice a year,”
Rothweiler says. “This includes a visual check of all components
concerning rust, leakage of hydraulic system, condition of rubber
and plastic parts, software function of the control system, condition
of the cable system, function of sensors, function of the drive system,
adjustment of drive system.”
Rothweiler also adds that at each service, Eccon documents the
status of the roof system and arranges a maintenance schedule for
the next service.
“With this system the maintenance team know in advance what
to do the next time. This is proactive, enables pre-calculation of
maintenance and avoids surprises,” she says.
“We work with the material contractors to reduce
the solar heat so we can go with varying degrees of
transparency. We do this by doubling or tripling the
layers of ETFE to prevent the higher sun levels coming
into the bowl,” explains Mehta.
Air flow can also be used if the climate is mild
enough, but there is no getting away from the fact that
if you put a roof on a stadium, operators will need to
keep the temperature down, which is typically done
mechanically using heating and ventilation systems
HVAC. However, they also serve another purpose.
“It can be dusty, which can jam mechanisms, and
humid. HVAC systems have to manage that so the roof
can last as long as it is designed to.
“When the roof is open on a hot summer’s day
the bleachers pick up heat, the field picks up heat,
and when we close the roof, we have to be mindful
of the heat build-up, so it can be a real challenge,”
Mehta adds. n
ROOFING
46 www.stadia-magazine.com September 2019
/www.stadia-magazine.com