What are green roofs?
Simple, it is any vegetation which is planted on the roofs and terraces of the buildings, also on the ceiling of the underground garages. It is an alive part of the building, which permanently constitutes the active biological surface, thanks to which according to the Polish law – 50 per cent of the green roof surface can be counted toward the compensation of the bio-terrain used for construction purposes. Green roofs, also called the fifth elevation, protect the building from cold, heat, water and wind, etc, and it is an esthetical element of the building.
Is this solution applied in the multi-storied office buildings? How does it look like?
Green roofs in Poland are usually gardens build on the ceiling joists of the underground garages. They are very practical – it is a sort of a recreation, they help to get an access, park the cars, they create footpaths for pedestrians or simply, they have esthetical value. Also, it is pleasant to look at its beauty, at the same time, they enable the ability to manage the greenness in the city. The plants on the roofs of the multi-storied building are also sowed, although definitely rarely. The main differences in construction show basic roof division in two types – intensive roofs (gardens) and extensive (multi-surface with low maintenance demand). On intensive roofs, parks with high trees, shrubs, alleys, benches, playgrounds, fountains and many other forms of small architecture can be created. The thickness of its base allows that, which is about 30 centimeters without upper limit. Intensive greenery on the roof is not for utility purposes, but it serves to recreate the active biological surface, which in our country is still rarely applied. Usually those roofs consist of a large surface, which may reach several acres. Although the base thickness from 6 to 20 centimeters does not allow the completion of rich and complex landscapes, extensive roofs are extremely popular in the world because of a good, set-up price ratio and the service costs to the actual profits.
What kind of advantages will the green roof installation bring?
The first advantage is of course the compensation value in the context of the duty of the active biological surface recreation, which is economical because of the increasing prices of the building plots in the city. Other advantages depend on the roof type. The intensive roofs allows the creation of the utility space for its users. They are very crucial architectonic elements which may be helpful when a rental or purchase decision is made. It can be a sort of a business card which signifies the prestige and rank of the place. On the other hand, extensive roofs, although modest, have other important advantages – from the owner’s or administrator’s point of view. Independently on the type, the green roofs efficiently protect the building from the wind, UV radiation, hail as well as the results of the snow clearance and falling of the roof different things. The roofs lower and delay the amount of the rainwater to the sewerages, lowering the sewage costs. They thermally isolate the building, which in the summer enhance the air-conditioning system. They constitute the fire protection of the roof. They improve the building esthetics, because cover with the greenery roofs, which we look at, do not frighten of the old, black felt.
And what problems can investors encounter when they decide on such a solution? How to overcome it?
The first and the main problem is the price of such roof. In Poland, the realization costs is relatively high, because of the low competition among the supplying and realizing companies. Comparing the amount of several euro for extensive roof in Germany, including the money purchasing power in both countries, it seems that in Poland, in the course of time, the price should gradually drop. In Germany, the extensive roofs are made by roofing contractors in simple technology of the one-layer roof with the dry or moist sowing with an application of stonecrop shoots. In Poland, the companies, landscaping designers or the suppliers are not quite convinced yet to such an easy technology. Intensive roof, which are more expensive but look much better, are gladly appraised and realized by the specialized, gardening companies. It is known that the cost of equipment of the intensive roof, which includes benches, lamps, fountains, playgrounds, allies or the greenery, is much higher than the cost of the materials needed for its building.
Another problem for the investor is the design and implementation process. Although the prestige of the landscape designer has become important in the building process, who because of the greenery role in sale goals (green marketing), which lead to the investment costs, is more often hired to a green roof from the design till implementation phase. Because of lack of professional license, s/he is performing a role of an advisor of the principal architect of the investment. It is more clear in case of the green roofs, then the vision of the landscape designer coincide with the necessity of taking into consideration the complex conditions coming from various sectors. In the project of the green roof implementation, many parts take place, constant communication, coordination and many changes conduction is required. Any mistakes are caught in the green roof implementation stage, repeatedly knocking the assumptions of the greenery project and the realization costs. On big constructions, it is often noticeable engagement of the investors by hiring the inspectors who control the greenery aspects. It is a natural consequence of the investor’s responsibility in reference to the demanding users – communities and the building’s management. However the inspector’s role is imprecisely defined. The supervision encounters with the lack of the cooperation coming from other supervisors of different sections. Since, the green roof requires a coordination of the cooperation of various sections, uncaught mistakes from earlier work can preclude the green roof installation from coming to live, even though the inspector will do his best to make it happen. General contractors, who undertake the construction of such housing area, will more often realize the necessity of the time and means green roof engagement. Sometimes it happens that the green roof is pushed aside. It is created as it goes. In the meantime, the delays of the whole construction cause that the green roof is created in parts and in the shortest period of time, which relates to the lack of perfection, later improvements and often serious expenditure of the contractor of the green roof.
How does the maintenance of the green roof look like? Do the season of the year mean a lot?
Once again the attention must be paid to the roof type. The intensive roofs needs to be taken care of like a regular garden (watering, mowing, fertilization), however, few additional things have to be remembered like: appropriate, intensive watering, proper fertilization due to the water permeability of the roof’s technical structures, constant control of the technical elements, like dehydration or waterproof insulation. The green roof care is similar to the one in a regular garden
The extensive green roofs do not require such an attentive care; it is not true, however, that they do not require any attention at all – it has to be remembered that the roof’s esthetics depends on its care. The watering is necessary during the growing stage of the plants, than the roof can be on its own. As far as the rest of the activities – the fertilization is recommended once a year. It is necessary however, to control the roof as far as dehydration and insolation, moreover, the removal of unnecessary plants, which are brought by the wind is crucial. The nursing is advised in spring. Since the loss of the greenery after the winter snow clearance might be the case, the extensive roof can require additional impaling.
Can you give any examples of the green roofs application in Poland?
The green roofs are commonly known in Poland, although the intensive are more often, it shows the increasing number of the extensive roofs. The green roofs has entered the canon of the Polish architecture, what is visible in case of the office buildings and other public and commercial investments. The forerunners are undoubtedly the library of the Warsaw University (2001) and the Supreme Court (2000). The green roofs as the alive “fifth elevation” appeared on such facilities as the Copernicus Science Centre, Bialystok Opera House, the train station in Wroclaw and Katowice, Museum of the History of Polish Jews or the Zlote Tarasy shopping center. The majority of the office buildings, built during the last decade, is equipped with a green roof, for example, Platinium Plaza, Poleczki Business Park in Mokotow in Warsaw, Business Park – located near the airport and Olivia Business Centre in Gdansk, Shy Tower high-rise in Wroclaw and many more. The green roofs will be found in practically en newly build district.
What costs does the investor have to take into consideration to install a green roof?
The roof cost can be divided into two ways – including or excluding the cost of termo- and hydroinsulation. Since the hydroinsulation has to be done on any type of roof, I will skip the calculation. The real costs of the green roof include the cost of the materials (greenery, roof substrates, drainages and geofibers), labor (installation and nursing) and materials supply and transportation (transportation to the construction site and the horizontal and vertical relocation on the site). As far as we are able to estimate the cost of the materials and labor, the third factor can drastically change the installation cost of the green roof. To install such roof, a special roof substrate has to be used (a special soil base), which is supplied in the loose form. The transportation of 1 cubic meter of the substrate to the garage will be much cheaper than using cranes to transport the substrate on the roof. In addition, it needs to be remembered that the material has to be delivered to the construction site, which influences the price. We can estimate the cost of the materials to the extensive roof construction in the classical technology, that is, net amount of 56-80 PLN/sqm for the multi-layer-roof (the stonecrop shoots – 10-15PLN/sqm, roof substrate 15-20 PLN/sqm, filtering geofiber 3-5 PLN/sqm, plastic drainage 20-30 PLN/sqm, protecting and absorbing geofiber 8-10 PLN/sqm), in the simplest technology of one-layer-roof net amount of 47-60 PLN/sqm (the stonecrop shoots – 10-15 PLN/sqm, 10-centimeter roof drainage substrate – 25-30 PLN/sqm, protecting and absorbing geofiber – 12-15 PLN/sqm). It is an estimated cost, including technology companies. Apart from that, the labor and transportation need to be added. New technologies are developing, in which a part of the substrate is replaced by a special polyurethane foam. In case of the intensive roofs, which are more complicated and rich, the installation price is twice or three times higher.
Does the green roof installation help in the LEED or BREEAM certification process, allowing to obtain a higher price?
It definitely helps in the LEED or BREEAM certification process. Each of these evaluation systems of the buildings, which are environmental friendly, include the criteria of the green roofs. Based on LEED system the roof’s presence will influence the score in terms of alleviation of the warmth effect. The BREEAM system awards points for the green roofs as an element alleviating environmental investment outcome and enlarging the water permeable surface. Since in both systems, the recycled materials are scored, in the world in green roof technology, in the roof substrate – the brick debris and the leaf mold are used. Also the drainage is made out of recycled materials. It is to be remembered that the green roof is not built for the certificates, which is awarded for the whole idea of the environmental friendly building. The green roof is one of such a solution, and it is distinguished for the fact that is an alive construction which needs something more than just a substrate and a drainage. It is not that pricy, it requires a different perspective, however. For a proper functioning, a green roof requires a biological live, which we often forget about. A great example are the Swiss, who proved that placing old branches on the roof, local substrate thickening, monoculture avoidance and an application of local plants cause that on the roof numerous microorganisms appear, along with insects and birds, which make the whole biosynthesis process conjunct, returning the nature just a bit of what it was taken from her.