British Science Week takes place from 11th to 20th March 2016 and it’s a marvellous celebration of everything that our scientists do for us. From healthcare to communication, air quality to space travel, science touches our lives in a myriad of different ways. So for this blog, I thought I’d look at the ways that scientific research has helped create the green roof revolution.
Science and Green Roofs
Urban roofs are largely unused spaces with huge potential.
Green roofing provides ample opportunities for better rainwater management, energy management, leisure space and even food production.
Science is finding ways for us to make the most of our rooftops.
We know that green roofs have a LOT of benefits. How do we know? Because scientists have measured and recorded their effects on insulation, biodiversity, air quality and rainwater management. Then that information has been used to maximise the benefits of green roofing. But here’s the thing, we’re still learning!
Research into green roof biodiversity
Many of the effects of green roofs are instant but some of them change over time. Biodiversity is one such thing.
It takes years and years for mini-beasts to establish their colonies on green roofs and some of the research is discovering which type of green roof is best for biodiversity in the short, medium and long term.
Sedums are commonly used on living green roofs. They offer a valuable source of pollen and nectar to wild bees and honey bees – and it doesn’t seem to matter how high the building is – the bees still find it!
Dr Gunter Mann has made extensive long term studies of the wildlife on green roofs. His research reveals the wildlife value of different types of green roof over time.
He’s compared and contrasted the wildlife populations that visit or colonise green roofs at different heights, with various different plant species, different depths of substrate and different sized roofs.
Dr Mann’s research has shown that all green roofs are valuable to wildlife.
The shallow substrate extensive green roofs typically created using the Enviromat green roof system tend to be more valuable as summer forage for bees and pollinators.
As substrate depth increases, so does the diversity of plant species that can grow on it and the variety of insects that are able to overwinter and breed on the roof.
A green roof with a deep substrate layer can support a wider variety of plants – if it has safe access it can even become a leisure garden or a productive garden. If it were a wildflower meadow it would provide useful wildlife habitat AND be low maintenance. A veg garden would need more TLC.
If you want maximum wildlife and your roof can take the weight, a 15cm layer of growing medium topped with Meadowmat for Roofmeadows would be a great choice. If the roof isn’t strong enough, an Enviromat green roof weighs much less – increase its wildlife value by installing it on as much substrate as you can and varying the depth. Maybe have a couple of areas of Meadowmat too if you can?
Research into plant growth on green roofs
The most visible component of a living green roof is the plant layer. All other layers are about ensuring that the plants survive. So using the right substrate (growing medium) and getting the right balance of nutrients is crucial.
Vegetable growers and farmers will already know that soil type affects growth and productivity. On a green roof, we need to optimise physiological performance very carefully. If the plants get too lush they’re vulnerable to frost and drought. If they’re not thriving, then the insulating, cooling and wildlife benefits of the green roof are threatened.
The growing medium also has a bearing on Stormwater management on a green roof. If the particles are too small, they could wash away and block drains. If they’re too large, the water retaining function of the roof is compromised.
Research into green roof substrates, such as that carried out by TM Young, GK Phoenix, DD Cameron, J Sorrill and T Edwards has been invaluable in helping growers, specifiers and installers to maximise green roof performance. And it’s the reason why we never ever compromise on the substrate quality when we’re growing Enviromat. Enviromat may not be the cheapest in the short-term but for performance and longevity we’re confident that it offers great value.
A sample of Enviromat sedum matting showing the layer of growing medium. Choosing the right growing medium makes a huge difference to a green roof’s performance. Garden soil is definitely not suitable. This substrate is well-drained, light weight , resists compaction and contains just the right balance of plant nutrients (although these will need topping up every year)
Green roofs and energy supply
This is by far the most exciting research to be carried out around green roofs.
PV panels are a great way to harness the energy of the sun to generate electricity. But they’re bulky and take up a lot of space. It’s only sensible that they should be installed on the roof where they’re out of the way and unlikely to be in the shadow of trees or buildings. BUT it gets pretty hot up on the roof in summer time and excessive heat reduces the performance of PV panels.
Combining green roof technology with pv panels is a successful way of harnessing the sun’s energy to support ourselves. The two technologies work together for greater efficiencies. Genius!
One study, conducted by the Department of Mechanical Engineering at The University of Hong Kong (another branch of science) concluded that integrating PV panels and green roofs generates 8.3% more electricity that the stand-alone panels. In economic terms, that means a better return on investment.