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 housing 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.

A HEALTHY GREEN ROOF IS AN ASSET TO A BUILDING Robert Allen, Production Manager and Green Roof Advisor 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

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.

Tel: 0800 061 2835 www.enviromat.co.uk

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Designing Green Roofs with maintenance in mind: Budgets and Buildings Budget: An extensive green roof is “low maintenance” not “no maintenance” clients should budget for two maintenance visits per annum

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 Kevin Docherty at Enviromat. Email [email protected]

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.

A steep slope is visually attractive but can be a challenge to maintain.

Inadequate drainage will damage plant populations

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.

Well designed drainage outlets do not allow debris to fall into the gutters and are easy to clear

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Designing Green Roofs with maintenance in mind: Budgets and Buildings 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.

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.

Water: Green roof plants will need to be watered in the first few weeks of establishment, and may also need irrigation during extreme 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

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Designing Green Roofs with maintenance in mind: Plant Choices 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:

Mixed sedum plants

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.

Aspect: Some plants detest shade, others embrace it. If you have an area that’s likely to be in permanent shade – eg behind PV panels, 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.

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Designing Green Roofs with maintenance in mind: Plant Choices 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.

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.

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.

Enviromat

Designing Green Roofs with maintenance in mind: How Regular Maintenance Maximises Performance 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.

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Designing Green Roofs with maintenance in mind: Troubleshooting 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.

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Designing Green Roofs with maintenance in mind: Useful Contacts

For help and advice with designing a small scale domestic green roof: Please contact Enviromat www.enviromat.co.uk Tel: 0800 061 2835