You were recently elected vice president of the European Federation of Green Roof and Walls (EFB). Tell us a little about the EFB’s objectives the work it carries out.
The EFB is the federation of the various national associations in Europe that handle issues relating to green roofs and walls. We encourage these countries to work together and we support the European Community with any open dossiers in this area. We establish a collective strategic plan every year and we share tasks throughout the year with the aim of achieving an organised working process on a European level.
The subject of green roofs has been an increasingly popular topic in recent years. Could they be one of the answers to urban rainwater management problems? If so, how?
This is essentially linked to the perception that green roofs can bring extremely interesting benefits to urban ecosystems, which include rainwater management, and with a highly favourable payback. The roof is the first part of building to have contact with the rain. If we were able to detain this water – and the sector is continually develop¬ing systems with large water retain capacities – we could greatly alleviate urban drainage systems. Apart from that, excess water would be channeled into the drainage system at a slower rate, which also facilitates its management. Rainfall peaks are on the increase, meaning that large volumes of water are generated in short spaces of time. In addition, cities are getting increasingly bigger, more built-up and waterproofed. Buildings are therefore being forced to adapt, meaning that green roofs are making a greater appearance.
Green roofs allow for the creation of gardens, urban vegetable gardens, as well as leisure and social areas that could not previously be used. Is the social role of green roofs also an important aspect for the industry?
Absolutely. In times of crisis in the past, people have used the roofs of buildings to produce food and this issue is receiving renewed attention today. If we consider that food travels an average of 2900 km to reach the end consumer in the United States, we soon realise that this leaves a huge ecological footprint. Bearing in mind that the world population grows by almost 240,000 people every day, we have a problem on our hands. Green roofs create an opportunity to produce food locally. In this respect, I believe that future buildings will also include underground gar¬dens for cultivation, with the aid of photovoltaic energy and hydroponics.
Could you give us a brief overview of the green roofs that are being implemented in buildings on a European level? Are some countries way ahead while others are only just beginning?
On a European level, this area is much more developed in northern European countries. Sod roofs were already incorporated into Scandinavian constructions as a part of their culture. These were wooden buildings that were finished with a layer of grass made with birch bark for waterproofing. This means that green roofs have been around for centuries. They were also the first to realise, in the 1960s, how these roofs improved the level of heat insulation, which was one of the first areas they worked on. Environmental aspects later emerged when it became clear that more vegetation in cities meant that more CO2 and other air pollutants could be captured, helping to improve the environment. From the 1960s onwards, some cities began to launch specific programs that fostered, or even insisted on the installation of green roofs, very often starting with local authority buildings. These roofs later started to ex¬tend to Southern European countries. You could say that this is a movement that spread from North to South. The Portuguese National Association of Green Roofs website (greenroofs.pt) shows an interactive world map of policies, where you can see the policies that are currently active in a range of cities.
Could you highlight some of the most important green roof projects in Europe?
This is always a difficult question because the most recent projects are usually the ones that spring to mind. For example, during the last meeting of the world federation, in Oslo, we visited a private building with a very interesting concept. The green roof was an optional feature that was developed to serve as a community area. The size of the balconies had been reduced in order to encourage people to use the roof. They designed a few private areas which were sold and, with this money, they financed the rest of the community area of the green roof. The most interesting aspect of this building was that, in comparison to others built at the same time, it was sold for 20 % more. This is an encouraging sign that the market itself is adapting and that there is an emerging demand for green roofs, without the need for political will or legislation for them to develop.
In terms of legislation, is the necessary legislation already in place or is there still some way to go before green roofs can become more widespread? Is the situation the same across Europe?
The subject of green roofs has been warmly embraced across Europe. There are many working groups and funding is available for research. Portugal is one of the countries that has stood out for its scientific work on the subject. No specific European Community directive exists in relation to this field that says, for example, that green roofs are obligatory. But the subject is certainly being encouraged and this has led the governments of each country, and consequently local authorities, to look into it as part of a decentralisation process. Indeed, if we look at local authorities, there is already a group of European cities that either require or encourage the installation of these roofs. This is the case in some German cities where the “user pays” principle is in force. If a building makes less use of the urban drainage system, then why not reduce the amount of tax it pays towards the maintenance of this system?
In relation to legislative matters, is this an area the EFB aims to get involved with? How?
The European Federation takes great interest in supporting the different national associations and promoting best practice. We also have to try to encourage countries that have similar climate conditions to work together. It’s in Portugal’s interests, for example, to work together with Spain, Italy, Greece and other Mediterranean countries with the same climatic conditions. But is also important to note that northern European countries are also interested in our know-how, because warmer and drier conditions are on the increase. A recent study suggested that London’s climate would be similar to that of Barcelona by 2050.
On a European level, and assuming that the solution has different implantation levels from country to country, how does the green roof market work in terms of project and construction? Are there already a lot of companies offering solutions and specific services for this area?
There certainly is a mature market in terms of solutions. It’s safe to say that there is a group of players and fairly large companies, and that we clearly have a solid infra¬structure in place to ensure that things will be done properly. At the same time, there is still some adventurism, a little DIY, which of¬ten means that the roofs do not perform as expected. But this is like everything else in the construction industry. If we lay poor foundations we’ll have problems, and if we take risks with waterproofing we’ll have problems. There are clearly defined rules and if we fol¬low these rules using the products and systems available on the market, we can achieve structures that could last 40 to 50 years without any problems.
Generally, and in economic terms, do green roofs offer more advantages than traditional roofs?
A green roof is always an added feature for a building. In other words, if we add an extra layer it’s only natural that this will affect the budget. It is sometimes possible to eliminate something from the system, for instance in terms of heat insulation, in order to save some money. But the fact is, a green roof is an extra cost. Yet we need to start looking at the life-cycle of buildings. We definitely need to abandon the idea of the costs on opening day and think about the long-term costs of running the building. From this point of view, the payback on investing in a green roof is extremely attractive. The energy savings go without saying. We will use less energy to heat and cool the building and thermal comfort is far superior. Being in a room with air conditioning at a temperature of 21° is not the same as being in a room with a natural room temperature of 21°. On the other hand, we will prolong the lifespan of our waterproofing, which instead of changing after 20 years may only need changing after 40 years. And finally, there are many other benefits that are more difficult to measure: less polluted cities, better health, more recreational spaces, increased productivity because we work surrounded by plants. These benefits last for the lifetime of the roof, so we should therefore look at the long-term investment.
In your opinion, what role could expanded clay have in green roofs?
Expanded clay is a historic material in the area of green roofs. It's excellent because it's extremely light and has characteristics that help to retain water, and can be used for drainage in green roofs or as an ingredient in technical substrates. It's an extremely versatile material and I even think that it could be used in ways we have yet to discover, given its potential for construction and also in the green roofs sector.
Could you give us one or two examples of projects where this material has been used with positive results?
I'm sure that Leca® LWA has been used in countless projects, but what usually happens is that when a green roof has been finished we don't know what's underneath. Even if we have access to the project, they may often have been changes, whether for technical or budget-related issues. But one example, in which I know a great deal of expanded clay was used, is Alcântara’s water treatment plant (ETAR). This project is simply iconic in Portugal, and which managed to place a water treatment plant – which isn’t usually a very attractive building – in the Alcântara valley with a fabulous design, linking it to urban vegetable gar¬dens that already existed.
How do you foresee the future of green roofs in Europe? One of the main trends in this area?
We are experiencing a time of transition. People are increasingly demanding nature-based materials, and buildings of the future will be obliged to demonstrate social and environmental responsibility. From a social perspective, there is the matter of food production. From an environmental perspective, buildings will be increasingly required to incorporate waste and use natural raw materials. I believe that all industry players involved with green roofs will be focusing on nature-based materials, as well as those that have proven carbon negativity. In fact, some areas of the market are already moving in this direction.
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