green roofs: designing for maintenance · 2016-06-21 · green roofs: designing for maintenance...
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Tel: 0800 061 2835 [email protected] www.maintenanceforgreenroofs.com
Green Roofs:
Designing for Maintenance
Green Roofs are becoming more mainstream. In some
UK cities, planners are being encouraged to introduce as
many living roofs as possible on to new buildings, from
green roofed bicycle sheds in the gardens of social hous-
ing to vast biodiverse roofs on commercial warehousing.
Enviromat work closely with the UK’s leading green roof
installation company; growing their sedum matting and
helping to research and develop new ways of
establishing plants on to green roofs of all shapes and
sizes.
The knowledge and experience gained in over a decade
of working with green roof plants and substrates is
shared with Enviromat’s green roof maintenance
division who work with green roofing companies and
their clients to ensure that the nation’s green roofs are
performing as well as they possibly can.
Besides a general lack of awareness for the value of, and
indeed the need for, green roof maintenance. By far
the biggest difficulty encountered by the Enviromat
green roof maintenance team is a lack of foresight at
the design stage. This document aims to remind anyone
who designs green roofed buildings of the basic needs
of the green roof maintenance operatives who will be
keeping the roof in good condition for years to come.
Mark Pawsey, Green Roof Supervisor at Enviromat
believes strongly that regular maintenance to keep
green roof plants in robust health really does
maximize all of the benefits of the living roof. More
importantly, he is convinced that maintenance
programs should be affordable...and that careful
consideration at the design stage can keep
maintenance costs under control
A HEALTHY GREEN ROOF IS AN ASSET
TO A BUILDING
Budget:
Clients should be made aware at the planning stage that a living green roof
needs annual maintenance if it is to perform as expected. Many of the
commercial green roof installers do include a period of maintenance in
their contract so that they can ensure plants have established before the
project is signed off; however, on-going maintenance is essential and the
client should include it in their annual buildings maintenance budget.
Maintenance costs vary according to access, planting plan, size of the roof
and it’s condition but a ballpark figure can be obtained from Mark Pawsey
at Enviromat. Email [email protected]
An extensive green roof is
“low maintenance” not
“no maintenance” clients
should budget for two
maintenance visits per
annum
Loadings:
When calculating loadings on the building, please factor in the saturated weight of the growing medium, the living plants, any
edgings, fixings and fall restraints and also, live loading for at least two people to walk on the roof twice a year.
Slopes and Drainage:
Two very important factors; Slope affects anchorage, access for
maintenance and also drainage. Good drainage is a must BUT, if it’s too
good (as in a steep slope) water will drain away before the plants can
benefit from it. If your roof slope is greater than 10 degrees, you would
be well advised to install an irrigation system and budget for at least
three maintenance visits per annum.
Be aware that water directed on to a green roof from other buildings can
potentially damage plants and if your design includes paths or walkways,
please ensure that these don’t adversely affect the drainage.
A steep slope is visually attractive but can be
a challenge to maintain.
Designing Green Roofs with maintenance in mind:
Budgets and Buildings
E n v i r o m a t
Well designed drainage outlets do not
allow debris to fall into the gutters and
are easy to clear Inadequate drainage will damage plant
populations
Health and Safety:
Health and Safety is not just for the installation stage of your green roof. It’s for
maintenance too. Safe access points and fall restraints are essential please;
Enviromat’s green roof maintenance team have our own safety clothing but we
do appreciate having anchorage points for our harnesses and lanyards.
Access:
This is one of the most common challenges for our operatives. People and equipment need to get on to the roof, and,
depending on the aspect and the planting plan, there may be debris to be carried down from the roof. If at all possible, an
internal staircase, or a fixed external ladder with fall restraints would be superb. On a large roof, operatives are required to
carry bags of plant food on to the roof…a winch system makes life much easier for them and also makes the job quicker…
ultimately saving on labour costs.
Water:
Green roof plants will need to be watered in the first few weeks of establishment, and may also need irrigation during ex-
treme drought and immediately after feeding. Choosing drought tolerant plants and the correct depth of growing medium
will considerably reduce the need for irrigation once the roof is established but please include a functioning water tap
somewhere in your design.
The result of inadequate maintenance on a sedum
roof.
Plant coverage has been lost...probably due to
lack of nutrients.
With no foliage to shade it from the sun, the
growing medium has dried out and will not be
effective at cooling the building in hot weather
Without the plants’ roots to stablilise it, growing
medium is easily washed into drains during a
rainstorm
Poor plant coverage or unhealthy plants are of
little benefit to wildlife; neither are they a pretty
sight
Designing Green Roofs with maintenance in mind:
Budgets and Buildings
E n v i r o m a t
Designing Green Roofs with maintenance in mind:
Plant Choices
E n v i r o m a t
Plant Choices
A green roof is a marriage between engineering and ecology. These are two disciplines
that don’t necessarily join forces in any other situation and so green roofing is a bit of a
learning curve for both.
Choosing green roof plants is a juggling act between the client’s expectations for
aesthetics, speed of establishment, budget and ability to care for the plants; planning
requirements such as local biodiversity action plans; local environment and growing
conditions on the roof.
If the conditions created by the engineering of a building are wrong for a particular plant species, it will be very difficult to
keep those plants in good health. If the plants are inappropriate for green roofing, the building may be damaged.
When choosing plants think of a green roof as a giant container garden and consider the following:
Depth of growing medium:
This will affect loadings on the building, but it is also vital that the chosen plants have enough growing
medium (substrate) to support them.
Sedums can survive in just 20mm of growing medium; a wild flower meadow will need at least 150mm.
Bear in mind too, the method of establishment…sedum blankets need no extra growing medium,
sedum plug plants will need to be planted into at least 100mm depth of substrate.
The deeper the substrate…the more likely it is to support unwanted plant species…so more weeding
for the maintenance team.
Mixed sedum plants
Aspect:
Some plants detest shade, others embrace it. If you have an area that’s likely to be in permanent shade – eg behind PV pan-
els, either make sure there is enough growing medium to support shade loving plants OR plan to have a plant-free area here.
In a sunny spot, make sure you choose plants that can tolerate intense summer heat as well as winter cold. Never forget that
the temperature on a roof is usually and exaggerated version of the temperature on the ground. Hotter in summer, colder in
winter.
Surrounding area:
If your green roof is in close proximity to deciduous trees, you will need to remove fallen leaves in the autumn time. Please
budget for this annual task and ensure debris can be removed from the roof safely.
Height of the building:
Altitude will have a bearing on wind speeds and ambient temperature; remember that even a slight breeze can dry out plants
in a remarkably short time. Look for low growing drought tolerant plants that are not likely to be buffeted about or scorched
by strong winds.
Mode of establishment:
Green roofs that are seeded or plug planted are likely to need more maintenance in the first 2-3 years than green roofs
created with vegetation mats: this is because gaps between the plants are a great place for weeds to establish. Where there is
complete plant coverage it is more difficult for unwanted plant species to invade.
Plant vigour:
Some plants are just too vigorous for green roofing, avoid anything with invasive root systems as they may damage
waterproofing. Be sure too that no one species is likely to out-compete everything else on the roof.
Mixing species
Wherever possible incorporate a mixture of plant species and varieties.
Even if biodiversity is not the primary reason for installing a green roof, it
is an important feature of any green space.
Incorporating several different species will mean that there is less risk of
all plants being wiped out by pests, diseases or bad weather; it will also
mean (hopefully) that there is a longer flowering period offering greater
benefits to pollinating insects and of course, more visual interest.
Mixed native species are an excellent choice for green roofing. Ideally
look for perennial plants (not all annuals will seed themselves successfully
year after year) that flower at different times of the year and provide a
source of nectar for as long a period as possible. Avoid really grassy
meadow-type mixes unless you are able to cut them back once a year and
remove all the clippings from the roof.
Low maintenance plants
Generally speaking, if a plant is happy in it’s situation, it won’t need a lot
of TLC but some types of planting will always need more maintenance
than others. If you are using your green roof to cultivate food crops, grow
shrubs, exotic plants or tender perennials, be prepared for extra
maintenance.
Meadow saxifrage; an early flowering native
plant ideal for use on green roofs.
This grassy roof is great for insulation, rainwater
management and biodiversity but at least once
a year it will need to be mown and have all the
clippings removed. OK on a single storey
structure like this but no so convenient on a
very tall building.
Designing Green Roofs with maintenance in mind:
Plant Choices
E n v i r o m a t
A stitch in time saves nine:
Nine compelling reasons to look after your green roof
1. Regular check-ups can spot problems with the visible
roof structure before they get expensive
2. Each layer of a green roof interacts with the other
constituents to form a dynamic system. A seemingly small problem in one area could
be detrimental to the whole roof if it is not addressed quickly enough.
3. It’s cheaper to spend a little every year to keep the green roof build up in good order
than it is to replace the whole thing when it fails.
4. A well maintained, healthy green roof will reduce the buildings’ energy usage, saving
money and reducing carbon emissions
5. A neglected green roof is unattractive and gives a bad impression.
6. A vibrant and well functioning green roof soon becomes a mini wildlife sanctuary. Our
experts can give you tips on developing your green roof to increase biodiversity.
7. A well functioning green roof could improve productivity by reducing sick building
syndrome
8. Unwanted plants such as tree seedlings establishing themselves in the growing
medium could damage the structure of the building if they are not removed as part of
a regular green roof maintenance regime.
9. A healthy, attractive, well functioning green roof can increase property values.
Designing Green Roofs with maintenance in mind:
How Regular Maintenance Maximises Performance
E n v i r o m a t
Designing Green Roofs with maintenance in mind:
Troubleshooting
E n v i r o m a t
Sedum matting on a green roof has not established
because of lack of water. This can be remedied in one
or two maintenance visits but it would have been
cheaper to ensure that it is easy to irrigate the roof
at the
Weeds will establish themselves if the desired
planting is not in the best of health. Choosing robust
plants that are well adapted to the microclimate and
then keeping them in good heart will help keep
weeds at bay.
Expect a healthy green roof to change its
appearance with the seasons. This cherry red
colour is normal for a sedum roof in winter.
It’s important to get drainage right before the green
roof build up is installed. Be wary of drains
discharging on to the roof. In this instance, the sedum
plants are not tolerating the wet conditions.
Designing Green Roofs with maintenance in mind:
Useful Contacts
E n v i r o m a t
For help and advice with designing a
large scale or commercial green roof:
Please contact Bauder
http://www.bauder.co.uk/green-roofs
Tel: 0845 271 8800
For information about Enviromat’s
Green Roof Maintenance Service
Please contact Mark Pawsey on 07787 288736,
Email [email protected]
Or visit our web site
www.maintenanceforgreenroofs.com
For help and advice with designing a small scale domestic green roof:
Please contact Enviromat
www.enviromat.co.uk
Tel: 0800 061 2835
Or visit our blog at http://greenroofsforordinaryfolk.blogspot.co.uk/