Green roofing – which system is the best?

The last 10 years has seen a rapid rise in the number and type of living green roofs being installed but which design features are the best?

Over the last decade, The UK has seen a huge rise in the numbers of green roofs being installed and some incredible changes in the innovation and the way these roofs are designed, planted and used.

10 years ago, when Q Lawns launched Enviromat Sedum Matting making green roofing available to people looking to insulate and improve the appearance of garden buildings, the concept of a living roof was just beginning to reach architects working on commercial buildings, but in the domestic realm green roofing was a) virtually unheard of and b) regarded as the domain of hippy, dippy eco-warriors.

Today, with thanks mainly to the gardening and home improvement media, green roofing is undoubtedly becoming more conventional; although the sight of a flowering roof or a vegetated balcony is still unusual enough to attract attention.

Thanks to innovations and research from around the world, the choices for green roofing materials, build ups and designs is expanding rapidly.

Every green roof is unique in terms of function, aspect and exposure, weight, height, plant choice, biodiversity, level of maintenance required and aesthetics.

Some living green roofs are purely for cooling the building and for creating wildlife habitat. They’re rarely seen, particularly if they’re on top of a tower block but nevertheless they’re vital in the fight against climate change and biodiversity loss. Colonies of honey bees have recently been introduced to a green roof on top of Canary Wharf in London. Even an “invisible” green roof can be productive.

Other green roofs are all about aesthetics. They can help blend a building into rural surroundings or they can add an extra “wow” factor to a project.

Sedum matting remains one of the most popular methods for creating a small green roof. It’s lightweight, so there are fewer issues regarding loading; it’s easy to handle and the build-up normally consists of fabricated drainage and water retention layers topped with a pre-grown blanket of drought tolerant succulent plants. It’s quick to install so labour costs are minimised and the customer receives an instantly green roof at a not-too-painful price.

Biodiversity is topical at the moment both at ground level and on the roof. On super-sturdy buildings we’re seeing an increase in the popularity for predominantly native, varied planting. Research in Sweden has shown that whilst a mixed species sedum mat provides a fantastic habitat for mini beasts and a great source of pollen and nectar for butterflies and bees there is greater diversity of both flora and fauna to be found on roofs where there are more potential habitats.

The typical biodiverse green roof is based on a deep layer of growing medium – the minimum is 150mm but often they are deeper and allow more plant species to survive. Obviously, the more growing medium used, the heavier the roof build-up will be and it’s vital that the building is able to cope with the extra loading. On a purposely designed new-build this shouldn’t be a problem, but on a garden building or a retrofit, it’s always wise to employ a surveyor or an architect to check that the building and the roof deck are able to support the green roof build up.

There is no reason why a sedum blanket roof shouldn’t be combined with a biodiverse roof….just work out where the roof is strongest (usually, but not necessarily above supporting pillars) and create deeper layers of substrate or some wildlife-friendly features such as log piles in the strong spots.

Dusty Gedge is President of the European Federation of Green Roof Associations and he is predicting that in the future, green roofs will benefit humans to a great extent – and not just through reducing energy bills.

“Food production is one on the increase and I think it will continue though I don’t think for real production – not cost effective. I think it will be more like market gardening before mass production, small scale producers producing local herbs/salads etc for local use in restaurants etc. I think it will also be part of a ‘social’ awakening whereby food on roofs brings communities together and to produce and make a little money. This is already happening in the states.”

There is a suitable green roof build-up for almost every building. Financially speaking, installing a green roof is a worthwhile investment but it’s something that you really only want to do once. That being the case, it’s important to get it right first time.

The green roof build-up needs to be correct for the weight bearing capacity of the building. It must be easy to access for installation and maintenance. If it’s to be overlooked, the roof should be aesthetically pleasing. If it’s to be used for leisure, correct safety barriers are essential.

If your roof meets as many of your requirements as possible, it’s the best build-up for you.

Learn more about green roof design?

Enviromat have created a guide to designing a sustainable green roof. “Designing for Maintenance” can be downloaded from the Enviromat web site or you can request a copy by emailing Angela Lambert at angelal(Replace this parenthesis with the @ sign)

Download the guide