Civil Engineering Reference
In-Depth Information
Green roofs
Green roofs increase thermal and acoustical performances of the roof, help manage storm-
water reduction, filter dust particles in the air and reduce stress on the waterproof mem-
brane. Less quantifiable effects include psychological well-being of users and providing a
habitat for wildlife species.
Green roof vary in number of layers and layer placement, but are characterised by a
single to multi-ply waterproofing layer, drainage, growing media and the plants, covering
the entire roof deck surface.
There are two main types of green roofs:
•
Extensive
: They have thinner and less number of layers so they are lighter, less
expensive and require very low maintenance. Extensive green roofs are built when
the primary desire is for an ecological roof cover with limited human access. The
minimum growing media or soil substrate varies from 5 to 15 cm. Fully saturated
weight ranges from 45 to 100 kg/m
2
. Low growing, horizontally spreading root
covers the ground with plant heights generally 40-60 cm.
•
Intensive
: They look like traditional roof gardens because a much wider variety of
plant material can be included, since growing media depths are increased. The grow-
ing media generally ranges from 20 to 100 cm, depending on the loading capacity of
the roof and the architectural and plant features desired. Fully saturated weights start
from 350 kg/m
2
. Lightweight solutions that do not significantly increase the structural
load on existing buildings make the application of green roofs possible also in refur-
bishment operations (Fig.
3.1
).
Fig. 3.1
The roof of one of the buildings at the Politecnico di Milano campus was retrofitted
with eight different types of green roofs, which are now being monitored for physical and ther-
mal performances (R. Paolini, GreenLab, Dipartimento ABC, Politecnico di Milano)
