Following last month’s blog about the world green roof congress, I promised the second revelation that will influence how I think about green roofing. From the macro to the micro, this inspiration came from Heather Bumble’s research into the micro-organisms living in green roof substrates.

Green roofs are gaining popularity as a way to help prevent species loss and support ecosystems in urban areas. Although habitat features like logs and stones with long flowering plants and varied substrate depth are known to encourage invertebrates, often ubiquitous sedum roofs are assumed to have some of these benefits too to a lesser degree.

After studying microscopic creatures like springtails and mites that live in  soil and form an essential part of a healthy ecosystem, Heather recorded that extensive  sedum roofs bring almost none of these  organisms to the roof when installed, and do not support sustainable communities when they arrive from elsewhere.

This shows the need for focused assessment of what ecological goals are expected from a green roof and careful design accordingly. We will be keeping up with developments in this area and making sure our product development follows mite-friendly advice.

It is always great to see new ways of doing things. The World Green Roof Congress in Copenhagen last week offered a chance to see Scandinavian styles of green roofing, ranging from large impressive projects in Sweden to tricky and challenging roofs in Copenhagen city centre.

For me there were two great revelations in the course of the week that changed the way I think about green roofing.  The first was two separate attempts by American green roof experts to formulate the holy grail of green roofing – the cost benefit analysis.

Because of the many variables of different green roofs and the diverse drivers and functions, this has always been difficult. The dependence on local incentive schemes by local authorities and water companies promoting reduction of surface water runoff has usually been considered the main financial motivator, followed by the desire to lengthen roof lifespan and in particular cases the energy savings from temperature regulation.

Now the picture has changed rather dramatically. While water is still a big driver it has been overtaken by another that was rather surprising: amenity. The increase in productivity of staff who were able to view a green roof was so great, and the reduction in number of sick days so marked that the financial payback was on average twice that of the water management incentives.

This has big implications for the quality, aesthetic and location of green roofs. Clearly any company with a roof overlooked by its own staff has great motivation to make sure they have a healthy, lush looking space.

However the huge impetus is on local planners to incentivise those who are not lucky enough to view their own rooftop. How much happier and more productive a city is will have more long term payback for citizens and politicians than even the noble credits of air cleaning, water collection and biodiversity support. And in these tough economic times this is exactly the kind of productivity boost business needs.

I will save the second revelation for the next blog as it deserves a good explanation, and will change from the wider view of planning to the microscopic view of substrate organisms!

How many species can you really fit on one roof?

The birds and the bees have been the focus of much attention recently, and finding creative and exciting ways of sustaining them has become much more than a new trend. This is not a marketing report for Ann Summers, but a reference to the ways in which biodiversity targets have filtered into everyday consciousness, from ‘save the bees’ to green corridors.

Green roofs can play a big role in providing space to support wildlife, among their many possible environmental functions. Putting the right species on the roof according to its location and the function you want it to perform is always important, and common advice to increase the variety of species on the roof  is generally designed to avoid the unhelpful symptoms of a monoculture sedum roof.

Putting more varied species on a green roof will help mitigate the loss of coverage should any species perform poorly in a particular year, and well as providing more visual interest and a better food supply for invertebrates at different times of the year. Common sedum roofs have a short flowering period, which is why meadowflowers are preferred for wildlife support.

Does it follow that the more species you put on a roof, the better? Some wildflower turf producers have taken this quite literally and seem to be aiming for a hundred species per roll. Certainly not all of these will survive on every roof, but the theory that starting off with the maximum possible and seeing how many last in the long term is interesting.

There are a couple of points worth considering before blasting your roof with as many species as you can. One is that if you are creating a habitat for particular species, then there will probably be supporting food plants specific to that kind of ecosystem. It may be more important to make sure these plants do well than to add lots of other species that might out-compete them. Another is that if the green roof is designed to gain BREEAM ecology points then there will be certain recommended species for the site, and finding a selection of these that are available at the time of planting may dictate how many are used.

Ideally with enough notice, your recommended plants can be grown to order. But this still leaves the question, how many species constitutes a good bio-diverse roof? The size of the planting area is important here. A modest roof area of 50 square metres with a good planting density of 30 plants per square metre will leave 1500 plants to order, trays of 100 plugs of a single species provide the opportunity for 15 different species. This allows quite a good range which, with consideration of flowering periods and local conditions, should provide well for many insects.

On smaller roofs this diversity can be achieved by planting plugs of key species which are long flowering and suitable for many insects, and adding sedum cuttings or seeded grass and wildflowers of other species to see what else can establish itself. With larger roofs one has the option to order just 100 of as many species as can possibly fit into the space. However it could be considered that once there are twenty different species present, all your main functions, flowering periods and support functions may already be covered.

Twenty is only a guide number and there are various exceptions, such as bio-diverse roofs with different substrate areas to support a mix of ericaceous and calcareous plants, and recreate different specific kinds of habitat. It is also advisable not to stick to the same twenty wildlife species on every roof, as this contradicts the essence of the word biodiversity and does not show consideration for climate and local ecology. I am merely asserting that twenty well-chosen species may be much more effective than one hundred indiscriminate additions that may have no relevance to the situation and ecosystem in question. I would also suggest that the distribution of the species mixed widely across the roof surface rather than in larger swathes of one or two species per section will be much more effective for the survival of a rooftop ecosystem with little maintenance, in contrast to normal ground planting schemes.

If in doubt, it is always best to consult an ecologist. However we aim to make some of the basic principles of roof greening accessible to a wider audience and with the help of ecologists at White Young Green and the online biological record database, we will be including in our catalogue pointers towards the best species for supporting biodiversity in a limited space.

If you want to find a green roof that really excites passion and inspires people to love the idea of green roofing, my advice is head to Sharrow School in Sheffield.  This is one of the most famous green roofs in the country, made by volunteers under the guidance of University of Sheffield expert Jeff Sorrill, and the crowning glory of a highly sustainable primary school.  In an area where few local residents get to venture out into the beautiful surrounding peak district, many wild seeds are blown down the valley on the wind and find a resting place on Sharrow School, bringing nature back into the city.

In 2009, two years after its creation, Sharrow was the first roof in the UK, and probably the world, to be declared a Local Nature Reserve.  With the great benefits to the environment, school children and local residents no wonder biodiverse roofs are gaining momentum in the UK, possibly set to break the stranglehold of sedum matting on the industry.

So how does one create such a great natural haven? Many brown roofs have been attempted up and down the country, and a few of these which have been targeted towards the protection of brownfield habitats for creatures such as the black redstart have been quite successful, but many have seemed to flop. Did you know that the ICC and other public buildings in central Birmingham have brown roofs? They certainly haven’t made the headlines or generated as much interest as Sharrow, and were primarily focused on research. But what makes the difference between a weedy, ugly patch of rubble and a natural roof top wilderness that sets pulses racing?

Well the location just down the wind tunnel from the peaks has clearly helped Sharrow, and not everyone can call up pioneering national experts to lend a hand. But learning from past successes and failures, here are a few tips that should help.

• Put structural planting in to start. Even Sharrow started with some plants that provided structure and protection for the visiting plants and seed sown neighbours. Many plants will self-seed and spread further onto your roof if you design the substrate to encourage them.
• If you are trying to blend in with or recreate a local wild landscape, look for appropriate species (frost hardy and drought tolerant) and have them pre-grown to add to your roof planting.
• Good germinators can be sown directly onto the roof and will grow over time, but do not expect all varieties to get going. University experts like Nigel Dunnett have come up with great seed mixes of around 30 varieties with the expectation that around half of them should do well on any roof – but you never know which half!
• Don’t think that a wild natural roof doesn’t need any maintenance. The drains will still need checking, and Sharrow School had acquired some cheeky fruit trees and willows that were starting to sprout up among more welcome neighbours.  If these were not spotted and removed then nature’s influence would eventually get out of control.

As with any green roof design, it is essential to take into account the location of the building and the needs of the users, in order to achieve a roof that becomes part of your local landscape or cityscape and is truly appreciated.

Biodiversity at RHS Chelsea 2012

Many people (myself included) will have enjoyed following the Chelsea Flower Show this week, or further north might even have taken part in Scottish Biodiversity Week. Following the international year of biodiversity in 2010 we have now entered the ‘biodiversity decade’, so it looks like this biodiversity issue won’t be disappearing any time soon.  At Chelsea there was certainly a strong focus on integrating wildflowers and plants for pollinators, making naturalistic and harmonious spaces a strong feature of the garden design.

But do you stick to native plants that need protection or use either well-trusted or adventurous long-flowering foreigners pleasing both to the eye and the bee? The debate has raged, as we have learnt that a frightening 97% of our natural meadowland has been lost since the 1930s and bumblebees and other essential pollinators teeter on the brink of extinction. Luckily the gardeners, horticulturalists and policy-makers of Great Britain have rallied to save the wildflowers and native species for their own sake as well as preserving the habitats and food sources of other wildlife. Now commercial developers gain ‘BREEAM’ credits for using native species over foreign ones, which are increasingly in demand on new constructions.

As an urgent message designed to shift the industry in a new direction, the calling had to be strong and clear: Native plants are better. But for a while now horticultural experts at the University of Sheffield have been trying to make the point that while we should certainly help to preserve native species, there are many benign and helpful foreign species that can work very well alongside natives to increase the variety of insects and overall flowering period of a landscape. By taking the native mantra too far to the exclusion of all else and limiting the palette of species, you are by definition restricting biodiversity. Also, as we can see our climate and weather patterns changing, surely foreign plants can help us adapt to new conditions and mitigate the damage. James Hitchmough and Nigel Dunnett, advisors for planting at the Olympic park, have put this message across strongly through James’ speech and Nigel’s show garden this year at Chelsea, and people should really take notice before we push our landscapes too far down a narrow track. It seems to me that any accountant could have settled this debate on principle from the very beginning: whichever direction you choose at the end everything must balance.

A hum-drum business - Much of the green roofing industry has noted an increasing demand for biodiverse roofs. Is this a symptom of eco-bling, some kind of clever marketing to associate boring businesses in ugly buildings with bees and butterflies and flowers? Or is legislation forcing people to take biodiversity seriously? Well yes, sometimes both of these are true but delve a little deeper and you will find a lively and creative new colony of eco-accountants (ecountants?) who are taking the matter to the heart of business.

A hive of creativity - Some of the current buzz-words like natural capital and ecosystem services reflect the adoption of research initiatives like TEEB (The Economics of Ecosystems and Biodiversity) by the public sector and their integration into corporate CSR. By definition true sustainability measures should provide long term advantages and returns for business, the tricky thing is to quantify these so that they can carry economical weight against short term schemes. This is what TEEB is doing, so that these benefits can appear on company performance statements and really contribute to their value on their ‘triple bottom line’ (3BL; People, Planet, Profit).

A fool and his honey are easily parted - Many wiser and more forward-thinking companies have already assessed the impact of dwindling biodiversity on their own industries and supply chains. When Adnam’s greened their brewery roof there was a clear link between aiding biodiversity and protecting supply of raw materials, but many more indirect advantages in education, health and the community are there to be had as well. It is the well-considered investments in thriving, living roofs that will gain the marketers their brownie points in the long term, and show up hastily hoisted sedum mat jobs for the lightweight greenwash or planning app box-ticking that tends to rile the conscientious consumer.

In for a Penstemon, in for a pound - For these ideas to take off the link between an organisation’s wellbeing and that of its environment should be clear, strong and lasting. Engaging employees with the project is a commonly overlooked step which misses so many opportunities for promotion of an organisation’s efforts, and neglects to inform stakeholders of the genuine benefits they are receiving. I am always amazed by how many inhabitants of green roofed buildings are completely unaware of their existence. Get your people engaged with your planet-protection activities to maximise the financial profit: 3BL for fans of bees and common sense.

(relating more to the green roof industry than the popular boy band)

On entering Ecobuild this year and searching for the green roof section my first reaction was disappointment. Where are all the big, lush displays I remember from last year? Where are the podium speakers from the Universities, the independent consultants on
their soap boxes in the middle of the hall promoting biodiversity, rain gardens, and green roofing best practice alongside community tree-planting schemes?

I did find Dusty Gedge and some industry stalwarts up in a gallery seminar room providing a good summary of what green roofing is about, covering the basics for the diverse casual visitors, as well as could be expected in a limited time.

Somehow green roofs just weren’t the star of the show anymore, seemingly overshadowed by Passivhaus and even green walls.

One of the most interesting things Dusty mentioned in his seminar was the European standard green roof training course being developed at South Notts College with Gary Grant, that will dramatically help close the skills gap and make sure that contractors and installers can confidently supply good quality green roofs on a larger scale that will perform the great variety of functions required from vegetated roofs.  This is a sure sign that green roofing is really entering the world of mainstream construction rather than occupying a niche reserved for environmental enthusiasts. So maybe green roofs don’t need to be centre stage any more – they are here and they are staying, leaving the stage for more new technologies to be showcased.

A closer examination of the green roof displays revealed some interesting changes that seem to back this up. Some of the leading names in green roofing such as ABG, Alumasc and Icopal have kept a good focus on green roofing whilst also making more room for their other complementary products, other SUDS or planted infrastructure solutions, making green roofs an important tool amongst a kit of green technologies which can be applied to different situations. Even roofing companies and waterproofing suppliers who outsource most of the greening of the roof were keen to have a little aesthetically interesting display to draw people in and prove their ‘eco-credentials’. There was also a notable increase in the number of sedum suppliers present, although many of the seasoned green roof companies had noted the increasing shift away from sedum matting towards plug planting and wildflower or biodiverse roofs.

Moving on from Ecobuild, back down to earth at the West Midlands Growing Green exhibition, there was much more widespread and positive experience of green roofs compared to the previous year. Again the larger developers and construction companies were using the Passivhaus technology to prove they were ahead of the game, but when examined all were looking seriously at the different green roofing options now available and how they will suit their particular needs.

I don’t wish to present the Passivhaus technology as a competition to green roofing for anything other than exhibition floor space, as it has many different challenges and results. It is much trickier to retrofit, it relies heavily on the educated behaviour of the building user as well as the installer, and is much more geared towards energy reduction than water management and biodiversity. In fact from what I have seen of the standard wall thickness of these heavily insulated buildings they must have a larger physical footprint per square metre of living space – therefore an ideal base for a good green roof. Most importantly, green roofs for all their multi-functional benefits and uses can’t make the property and construction industries sustainable all by themselves. The really successful people know that to stay truly ahead of the curve you must see that the curve will bend in many directions; the successful combination of all these new strains of sustainable technology will be the key to future building practice.

The green agenda and the blue agenda require equal attention, as does the biodiversity agenda (yet to be designated a colour). Let’s leave One Direction to the world of pop music and enjoy the multi-focused progress towards an increasingly turquoise future.

Succulent sedum and delosperma species that are so prized on green roofs for their capacity to survive by storing water in their leaves and respiring at night are great in times of scarce water supply, drawing on their natural reserves so that artificial irrigation is unnecessary. But how do they cope with the snow?

Rather than delving into the plant physiology, it’s easier to think of their natural habitat – dealing with nature’s extremes on the side of a mountain with no care at all, these plants will deal with snow, frost, wind and high temperatures year on year without batting an eyelid. It is even more interesting to note that those hardy plants left outside seem to do better over winter than some of their relatives indoors. When they do show signs of stress or damage it is when they have had too much water and are not using their natural abilities to any effect.

What does this mean for your green roof? Well clearly different plants can take all kinds of rough treatment. There are two kinds of approach to roof planting: either put a varied range of hardy plants on you roof and see which ones suit it best and survive, or judge the particular extremes in each situation and handpick plants known to thrive in those conditions.  You can follow simple rules of thumb like putting more drought tolerant species in the dry southeast than you would in the rainy northwest, but with some peculiarities of local climate and roof conditions, and future climate change it can be challenging to predict just what plants will be right. It is wise to accept that low maintenance bio-diverse roofs will eventually settle to their own evolved ecosystem having used your planting scheme merely as a starting point, in the same way that you will never find an identical arrangement of plants on any two mountains.

As the winter sets in for good,  I took Tom, Boningale’s Business Developer and his new camera out to inspect the ground level test rigs we created last September alongside our first green roof on the office at Boningale to see how our hardy little plugs are doing.

I am very pleased to report that over the mild autumn even the slower alpines have established very well into the substrate. They have grown out far beyond the bounds of their original plug and, as this Delosperma shows perfectly, there are already new shoots forming in the centre.

Having a healthy foothold in the substrate before the tough weather sets in is important to reduce failure rates, which is why green roof planting is recommended in autumn and spring. Using a good sized, healthy plug to start with gives you the best start and ours are especially grown to encourage integration into the harsh mineral medium.

We’re now very excited to see how they look in the spring once the cold weather eases off and they come into flower.

This shows what happens when grasses take advantage of high nutrition and take over a sedum roof. They then die out and get patchy during dry spells and there is not enough sedum left to keep going.

We were thrilled to see so much press and online attention for the launch of our website last month, and would like to thank everyone for their interest – including Hortweek and the charming Ian Perry from BBC Shropshire who was our new green roof’s first official visitor.

This month, however, it’s time to come back down to earth and focus on the growing media, or ‘substrates,’ which are really the most important part of your roof system, and the part most commonly misunderstood.

With the help of the soil scientists at the University of Sheffield, Boningale is developing a new range of substrates to suit different types of roof, budget, and locations in the country. Keep an eye on our ‘Latest News’ page for details of their release, and an easy-to-follow guide to choosing the right blend.

If you want your roof to cope with different extremes year on year, you will have to give it reasonable support. In order to do this whilst making sure you achieve all your environmental and aesthetic requirements, the main things to consider are the depth of the substrate and the level of nutrition you provide.

Depth can be an issue for buildings with a limited load-bearing capacity, or in projects where quality is sacrificed to save initial construction costs.  However in the long term deeper substrate levels can save you money:

• Deeper substrates hold more water, so there is less need for other water capture mechanisms such as costly underground tanks to ensure zero surface runoff.
• The extra water stored by the deeper substrate will be accessed by the plants in times of drought, keeping the plants looking healthy without irrigation and reducing the risk of failure.
• The deeper substrate level can support a much wider variety of plants because their roots will reach down to slightly different levels to avoid competing with their neighbours. This will help with achieving greater biodiversity and gaining BREEAM points, and give a better aesthetic display.

Nutrition is provided by the organic element of the substrate, which is typically 10-20% of the mix for extensive roofs. The nutrition level of the substrate will determine how many species can grow on your roof and how much maintenance it needs.

• High nutrition supports more species, which is good for an elaborate roof garden but will require more maintenance to remove unwanted visitors.
• Low nutrition will support a range of carefully selected plants to be self-sufficient without risk of being invaded by aggressive grasses that could push them back.
• By creating a stable ecosystem on the roof, you can ensure that the nutrition levels will maintain themselves as plants gradually die back and decay, and are replaced with new growth. There should be no need to add artificial fertilisers to your roof!

You can also follow our progress on the green roof media on Twitter,  @boningaleroofs.

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