Green Roofs - Living Architecture Monitor - Fall 2019 - 24

RESEARCH

WHO IS THE GREENEST CITY OF THEM
ALL? HOW SHOULD THE GREEN ROOF
WORLD MEASURE SUCCESS?
BY DUSTY GEDGE, PRESIDENT, EUROPEAN GREEN ROOF ASSOCIATION

Measuring the success of green roof policies and strategies should be a key
element of what a city does. Success for cities is different from measuring
market size and value. From the green roof industry perspective
market value of course is an imperative - individual company's sales and
installations increasing year on year will be key. Yet from a city perspective
sales mean little. It is area that counts!

ver the years of my work in London campaigning and
providing policy and design advice on green roofs the key
question has been - what impacts have the London Policy
had since it came into effect in 2008. The only way to answer
that question was to map every single green roof! And for a city
the size of London that is not a casual endeavor. So, over the
last few years, I personally set out to undertake the exercise. The
results of this mammoth mapping exercise form a very important
element of the new London green roof report published in April
this year. The data provided includes infographics for the whole
of the Greater London area, each London borough and for the
Central Activity Zone, a key planning zone in London.
Whilst the exercise was aimed at charting the success of London's policy, we also published an estimate of the area of green
roofs in various cities in the world to provide some idea of the
success of London when compared to other leading cities. This
table is based on some research undertaken by the Humbolt University in Berlin, as yet unpublished, that I was party to because
I was providing data on London for 2015. Of course, part of this
exercise intended to show that London is on par with many other
cities cited as being at the forefront of the green roof revolution.
As a Londoner with a degree of ownership of the policy, the intention was to show the doubters that London was on a par with
other cities beyond Germany, Switzerland and Austria.
There is not space to review the table, (opposite), in detail,

LIVING ARCHITECTURE MONITOR / FALL 2019 / 24

but it does bring into focus
how data is collected in a city
and what that data actually
means. At present, the data
collection methods used vary
from city to city. I do know
that certain cities in the world
have mapped in detail their
green roof areas - namely
Dusseldorf and Vienna. Others
have used permit tracking,
some have done so manually.
Currently, there is no accepted
method for tracking green roof
installations.
The other question is how
best to compare cities of different sizes and populations.
One key element I took from
the original research in Berlin
was to present data not as total
areas - big numbers always
grab attention - but as the
area of green roofs per citizen.
This relates to the idea of the

amount of green space per
urban citizen as an indicator of
health in cities proposed by the
World Health Organisation.
Considering the two most
successful green roof cities in
the world, Basel and Stuttgart,
provides a perspective on the
use of this metric when it
comes to green roofs. Whilst
Stuttgart's total area was
twice as much as Basel's in
2015, Basel has over 5.71m2/
per person (PP) compared to
Stuttgart's 3.38m2/pp. Does
that tell a better and more interesting story than total area?
I think so.
More work needs to be
done to refine methods of
calculating green roof area
and how best to use the data
to compare cities and work to
improve policy development
and implementation.
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Green Roofs - Living Architecture Monitor - Fall 2019

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