Green Roofs: Designing for Maintenance 2016-06-21¢  Green Roofs: Designing for Maintenance...

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    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


    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



  • 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

    An extensive green roof is

    “low maintenance” not

    “no maintenance” clients

    should budget for two

    maintenance visits per



    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


  • 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.


    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.


    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


    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


    Poor plant coverage or unhealthy plants are of

    little benefit to wildlife; neither are they a pretty


    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


    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


    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 any