is a Green Roof or Living Roof - History and
Essentially a living roof forms
a weatherproof covering with various layers
supporting a range of plant cover. For some
time now central Europe has led a resurgence
in the installation of living roofs driven predominantly
by the need to adapt to changes in climate and
of green roof / living roof and application
There are many forms of living roof but for
ease of explanation they tend to fall into 2
main categories: extensive and intensive. A description
of what that actually means can be found below
with the addition of the bio-diverse roof which
is fast becoming the covering of choice for
many developments. These categories are fine
for quick and simple reference but many feel
that they are restrictive as its common practice
to combine two or more types on a single installation.
Example of a Sky Garden Extensive Green Roofing System to a domestic Flat Roof
Extensive – an extensive living roof is not normally
intended for human use and is unquestionably
the most popular form. It’s relatively
cheap to install, has lower weight loadings
and requires minimal maintenance. Usually the
plants are set in a light-weight growing medium
or substrate of a depth of between 20mm and
150mm. The plants themselves tend to be highly
resistant to drought, ground hugging species
such as sedum.
Intensive – intensive living roofs are very much
intended for human use and as such take on a
more ‘landscaped’ feel with deeper
substrates (at least 150mm up to a metre and
beyond) catering for a wide variety of grasses,
shrubs and trees. Maintenance is both essential
and regular as lawns need mowing and shrubs
pruning – an irrigation system should
also be installed.
Diverse/Semi Extensive – the
principles behind these types of roof are driven
by ecological concerns. Pioneered by the Swiss,
the bio-diverse roof is steadily becoming a
more common feature as policy makers seek to
replace lost habitats for local flora and fauna.
Sometimes known as ‘eco’ or ‘brown’
roofs they do not always cater for everyone’s
Example of how you can even create a beautiful green roof on a pitched roof courtesy of Sky Garden
Often site debris such as crushed brick
and concrete is used as a growing medium which
is applied in a more landscaped way with variations
of depth enabling mounds and craters to be formed.
This allows a greater variety of mostly indigenous/local
species to colonise.
The installation of logs,
small rocks and sanded areas encourage invertebrates,
birds and even lizards to use the roof. Initially
the roof will look no better than a rough, stony,
weed-infested area but in time will develop;
constantly changing as different species come
to the fore or take up residence.
growing and flowering seasons a mature roof
can resemble something akin to an English meadow.
Many people think they look messy and unkempt
but in fact these roofs do more for the environment
than sedum-based and intensive roofs.
The National Osteoporosis Centre Gets an Eco Friendly Green Roof
Protection Fleece and Resevoir Board
Laying the Substrate
Laying the Seedum Blanket
Finished Extensive Seedum Roof
a Living Roof? What are the Benefits?
Consider this if you feel that your efforts won’t
impact - figures by research institutes show that
there is some 350sq/km of global deforestation
per day and up to 120sq/km of global urban development
To be able to re-green impermeable
surfaces such as roofs gives us the ability to
readjust the imbalance – plants store carbon,
therefore, if we have more plants we can store
more carbon. Living roofs won’t save the
world but they serve as a fundamental tool with
which to address the problem.
Much as the environmental
arguments are compelling there are also very obvious
benefits of creating a pleasant environment in
which to live – something colourful perhaps,
ever-changing and ultimately inspiring.
Features and Benefits?
& Value – using the rooftop as an
amenity where people can work, relax or socialise
is a considerable benefit these days where
land and space is at a premium. The extra living
space adds value to the property.
- Reduction of Urban ‘Heat Island’ – It has been proved that where there
is urban sprawl there is an increase in temperature
caused by impervious surfaces. As temperatures
rise, air quality is compromised. Living roofs
cool and steady the temperature and act as a
humidity control thereby improving air quality.
Water Management – one of the key characteristics
of living roofs is their ability to retain significant
quantities of water and to release it through
slower run off and evapotranspiration (a combination
of evaporation and use by the vegetation).
means less pressure is exerted on the sewer
system thereby reducing flash flood risk. It
may even be a viable option to use a living
roof as an attenuation system rather than constructing
of Dust & Pollutants – the vegetation
absorbs carbon and stores it. This is known
as carbon sequestration. Research on extensive
roofs in America shows that more than 500 grams
of carbon per square metre can be stored in
this way. It is well documented that the vegetation
also filters out other airborne dusts and pollutants.
These processes improve the quality of the air
Habitats – bio-diverse roofs provide habitats
lost through development.
to Planning Consent – local authority
policies are increasingly favourable towards
the installation of living roofs.
in Power Demand – the insulation capacity
of a living roof is problematic as a fully saturated
roof will act as a cold bridge. Nevertheless
the roof is not always at full saturation point
so over the course of a year it has been proven
to effect the power demands of a building -
less demand for heating in winter and cooling
Aesthetics – [show picture of a flat roof
next to picture of green roof] Text –
which roof do you prefer?
Materials – The system we use makes use
of recycled plastics within build up and wherever
possible we use site debris as a substrate.
a Green Roof / Living Roof Considerations
- Financial - cost, of course, is a fundamental
factor when making decisions but it shouldn’t
be the driving force. Examine what the motivation
is for installing a living roof – most green
roofs will, to a greater or lesser extent, tick
all the boxes above but to personalise your own
its worth mulling over the following considerations:
- Weight – weight loadings are vital to calculate.
On a new build this will be sorted by the architect
but with a refurbishment it may be necessary
to call in the services of a structural engineer
as supports may require strengthening. Weights
are calculated as ‘saturated’ i.e.
when the roof is totally sodden with water.
As a guide a simple extensive roof will command
a saturated weight of around 100kgs/sq/m.
& aesthetics – do you want a picturesque
garden with many flowers and exotic species?
Or a more rustic scrub/meadow style that will
provide a genuine habitat for local fauna? Or
a combination of the two. Or a pitch and putt?
Or a vegetable patch? All these and more are
possible. You are only limited by your own imagination...
light-weight systems – be aware that there
are systems on the market that are light weight
and as such are quite cost effective to install.
There are concerns with this type of system
as they are nowhere near as effective. Fundamental
layers in the build up are often removed or
drastically reduced, weakening the system as
a whole. These roofs will require more maintenance
and are at more risk of dying off during prolonged
periods of drought. Whether your motivation
for a living roof is ecological, commercial
or purely aesthetic, it is a better option, long-term,
to consider a more well balanced design.
- Maintenance – the maintenance requirements of a living
roof centre around watering, feeding and weeding.
Generally, extensive and bio-diverse roofs require
considerably less than an intensive one. However,
it really depends on what your vision of the
The first 12 months of a living roof’s
life is the most crucial whilst the root systems
establish so there would be a basic requirement
to feed during growing periods and to water
during prolonged dry spells. After that the
main requirement will be for weeding out any
invasive or unwanted plants which may spoil
the balance of vegetation.
If aesthetics are
not a consideration then roofs can be left pretty
much to their own devices. With intensive roofs
it is unquestionably necessary to have some
sort of continued maintenance programme as lawns
will need mowing and shrubs pruning and it may
be necessary to enlist the services of a professional.
- Guidelines – how do you ensure that you have a good
design? Most quality green roof suppliers and
installers adhere to the German FLL (Forschungsgesellschft
Landschaftsentwicklung Landschaftsbau e. V)
guidelines as they are currently the only ones of any
FLL is an independent research
organisation set up by the German Government
to develop a set of guidelines on all aspects
of installing and maintaining green roofs. A
copy of this volume is available in English
Installation Build Up
- Waterproofing - ensuring that you have a sound
waterproof membrane as a base is essential.
Some waterproofing systems are not root resistant
so a root barrier will be required. To decrease
the likelihood of there being a breach some
sort of leak test is also recommended.
- Protection Fleece – much like a carpet
underlay this layer protects the membrane from
any abrasives that may work their way through
- Drainage/Reservoir Board – this preformed
plastic layer mimics the profile of egg cartons
and is used to drain and store water. Available
in a range of depths, dependent on the type
of roof garden to be installed.
- Filter Fleece – much thinner than the
protection fleece, this one is laid between
the drainage board and the growing medium (substrate)
to prevent clogging.
- Substrate – a growing medium can take
many forms from expanded shale and pumice aggregate
to on-site debris such as crushed brick and
concrete. It is vital to achieve the correct
depths for the plants above – thinner
substrates require more maintenance, store less
water, cater for fewer species and can have
reduced survival rates. If using the pre-grown
mats you should work to a minimum of 40mm depth
as the mat itself usually has about 20mm of
substrate. If plug planting or seeding it is recommended
that a depth of 50mm will be sufficient. Remember
that greater depths of substrate mean greater
benefits all round.
Plug-planting – this method requires the installer
to plant around 10 single plants per square
metre. The coverage is not 100% initially
and it will take around 12 months for a
full establishment of vegetation. The advantage
of this particular method is that you have
a great deal more control over species selection
and aesthetic design.
Hydro-seeding – this is a popular
method on the continent as it’s quick
and very cheap. After the substrate has
been laid, shoots and seeds are broadcast
over the relevant areas and a mulch of fibres,
fertiliser and water is hosed over the roof
from a tanker lorry below. Over a period
of 12-18 months the shoots will develop
and provide coverage.
County Flat Roofing we use the Diadem green roof
/ living roof system as they provide a wide range
of products and options for almost every eventuality.
Quality and durability are hallmarks of the brand
which use recycled materials wherever possible.
Diadem is fast becoming an influential brand in
central Europe, having originated in Hungary
and having a portfolio of prestigious projects across
the globe. Growing mediums and vegetation are
normally sourced from UK companies. Should you
require any further information or would like
to request a brochure please call us on 0800 09 88 271 or contact
Maintenance & Warranty
programmes for living roofs are normally discussed
before installation so that the client understands
what levels are required. There are basic minimum
requirements for all roofs but the amount of watering,
feeding and weeding increases with the complexity
of the roof or the client’s vision of it.
Maintenance can be carried out either by the client,
a landscape contractor or arranged through County
Flat Roofing Ltd.
carried by the whole system from waterproofing
upwards can be instated for 10, 15 or 20 years
insurance backed, giving you peace of mind.