G
reen roofs are evolving rapidly,
transforming from a specialist
eco-feature to a more mainstream
technology which can be seen on new
homes of all shapes and sizes. However,
the success of a green roof depends on a
number of factors, so self-builders must
not only consider the structure itself, but
the location, orientation, shading and
climate of their site.PLANNING AT DESIGN STAGE
While it may appear that planting can be
decided at a later stage, it is important
that these decisions are considered at the
design stage as the roof build-up impacts
on the planting possibilities. For
example, wildflower meadows are a
popular choice for large expanses of roof
surface, but they need plenty of moisture,
which means designing the roof to
accommodate the load and a greater
depth of reservoir core, as well as
necessary growing medium to keep the
green roof healthy. Alpine planting
however needs much less water to thrive,
which influences the load bearing
capabilities required from the roof.A WATERTIGHT SOLUTION
The most vital element of the green roof
is the waterproofing membrane which is
used to create a watertight barrier
between the roof substrate and the
green roof system. The membrane should
be flexible enough to cope with any
post-build settlement, tough and durable
enough to cope with the load bearing
requirements of the planting medium,
and have a sufficiently long service life to
make the green roof viable.
A common green roof design would
typically consist of an inverted warm roof
build-up, applying the waterproofing
system to the roof substrate, followed by
the insulation, and then the green roof
elements. This can add an extra layer of
protection for the waterproofing
membrane as it is cushioned underneath
the insulation.
However, a cold-applied liquid
waterproofing solution can be installed
either below or above the insulation,depending on the type of insulation used.
This is because these systems are FLL
certified as root resistant, so there is no
risk of root damage to the integrity of the
waterproofing membrane, even as plants
mature and their root size increases.
Consulting the waterproofing
membrane supplier for technical support
can help determine the right specification
in this regard.LOCATION IS KEY
Another key consideration during green
roof specification should always be the
location and prevailing climatic conditions
as these govern the amount of light,
heat, shade and moisture the roof will
receive. The influence of surrounding
buildings, which can also affect shading
levels and exposure to winds, also need
to be taken into account. These factors
should be assessed collectively to
determine the viability of different types
of planting.
Of course, no matter how carefully
the planting is considered, without
proper maintenance, the green roof will
not thrive post-installation. Establishing a
maintenance plan including associated
costs needs to be factored in at the
design stage for the green roof’saesthetics and benefits to remain durable.SPECIALIST GUIDANCE
Green roofs have significant advantages
for the environment – climate control,
storm water attenuation, noise and
pollution reduction and heat
insulation. They protect against thermal
gain and offer an additional habitat forThe
waterproong
membrane should
be exible, tough
and durable, and
have a
sufciently long
service life to
make the green
roof viable
Victoria Ramwell from Kemper System discusses specification best practice
and the key considerations for green roofs, including design, location and
waterproofing membrane
Going green
BUILDING ENVELOPE (ROOFING & CLADDING)september/october 2019 http://www.sbhonline.co.uk 55