A Green Building Envelope: A Crucial Contribution to Biophilic Cities - Biotechnologies and Biomimetics for Civil Engineering - page 147

Table 6.2 Overview of differences between extensive and intensive green roofs

Criteria Extensive Intensive

Field of
application

Flat or sloped roof up to 45
(1-7 %)

Flat roof

Substrate
height (cm)

5-15 [25

Layers Multi-layered Multi-layered

Weight of
substrate (kg/
m 2 )

50-170 [300

Vegetation Drought resistant, low growing

speed, sedum, herbs, grass

Species with higher requirements for
water and nutrients, grasses, trees, shrubs

Use Habitat for animals Additional living space for people

Ecological compensation Recreation area

Rain water management Meeting area

Protection of roof material Local food production

Insulating capacity Insulating capacity

Water
retaining
capacity

ca. 30-70 % of the annual
precipitation

ca. 30-99 % of the annual precipitation

Maintenance Low High

Indication of
costs (€/m 2 )

20-30 [60

A green roof consists in essence of five different layers. The first layer on top of
the regular roof construction is the waterproofing layer or membrane (1). This
layer protects the roof against water leakages. Then there is a protection and
storage layer (2), which prevents plant roots from growing through the roof
package. This layer also keeps the whole green roof construction in place. The
drainage and capillarity layer (3) buffers rainwater and drains surplus water. The
root permeable filter layer (4) filters small particles out of the rainwater, to prevent
them from ending up in the water drainage system where they might lead to
blockages in the system. The final layer of the green roof is the growing media or
substrate layer (5), in which plants can root. The thickness of this layer partly
depends on the type of plants on the roof (Köhler et al. 2012 ). Table 6.2 gives an
overview of the general differences between green roofs and is adapted from
Köhler et al. ( 2012 ).
Brenneisen ( 2003 ) and Kadas ( 2006 ) conclude from their researches that green
roofs contributes to preserving the local habitat. Green roofs are mainly inhabited
by insects like beetles, ants, bees, and spiders. However, on some roofs uncommon
and even rare species of spiders and beetles have been discovered (Brenneisen
2005 ). Furthermore, Brenneisen (2007) found also differences between extensive
and intensive green roofs, as research done in Basel (Switzerland), shows that
mainly because of the thin substrate layer (extensive green roof) less species can
develop. A thin substrate layer is beneficial from a cost perspective, but for