Environmental and Climate Technologies 2013 /3_________________________________________________________________________________________________ 72 Extensive Green Roof Ecological Benefits in Latvia Rihards Rušenieks 1 , Agris Kamenders 2 , 1-2 Riga Technical University Abstract – Extensive green roof ecological benefits are studied in this paper. The research contains a brief explanation about green roof technology and green roof ecological benefits. Green roof capability to retain rainwater runoff by accumulating it in storage layers and conducting it back into the atmosphere through evapotranspiration is studied and modeled. Modeling is done in Stormwater Management Model 5.0 software. The model is based on an existing warehouse-type building located in Riga and hourly Riga climatic data of 2012. Evaluation of the model is carried out and future study fields of green roof ecological benefits are discussed. Keywords – green roof, extensive green roof, rainwater retention, green urban building, urban planning, energy efficiency. I. INTRODUCTION Green roof technology is becoming more and more widespread in the world. Apart from esthetical value, green roofs have many ecological benefits as well. Green roofs are basically vegetation layers which are put on the roof of a building (either on new buildings or refurbishing existing ones) with supportive layers. Two types of green roofs exist – extensive and intensive systems. An extensive green roof is lightweight (60 - 150 kg/m 2 ), non-habitable by people. The vegetation consists of grass, moss, succulents, stonecrops, irrigation and maintenance is not required. Intensive green roof systems are roof gardens, which are heavyweight (180 - 500 kg/m 2 ), fulfill a recreational function with the possibility of urban gardening. The vegetation may be shrubs and trees, and irrigation and regular maintenance is required. Intensive green roofs are more suitable for areas with high population density, but in case of Latvia (and other Baltic countries) extensive systems are more appropriate. Extensive green roof consists of several layers. These layers are (from bottom to top): Waterproof layer. Forms the base of the green roof, protects the structure from impact of water; Insulation layer. This layer is optional on any roof, it prevents heat loss in the winter and cool air conduction in the summer; Drainage layer. Provides preferable conditions for plant growth by ensuring aridity in soil and preventing anaerobe environment. This layer also drains excess water from the soil to the roof’s drainpipes after heavy rainfall; Filtration layer. This layer prevents soil particles from washing into the drainage layer, causing drainage blocking and reducing flow; Soil layer. Soil is necessary for maintaining vegetation. Natural soil is too heavy to be placed on roofs. Soil must be lightweight and also must preserve a certain amount of water, allowing excessive water to dry, and the soil must contain plant nutrients, at the same time preventing them from washing out to sewage; Plants. In selection of plants An important aspect in the selection of plants is the esthetic requirements. Different plants change color throughout the year. However the main criteria are plant vitality and resistance to unfavorable conditions. Frequent choice is Sedum, Delosperma, Euphorbia un Sempervivum.[1] II. ECOLOGICAL BENEFITS IN CASE OF LATVIA Green roofs have many ecological benefits. In case of Latvia, these benefits could be pointed out as the most important: • increase of building energy efficiency (insulation and passive cooling). Green roofs act as an additional insulation layer, but passive cooling occurs by conduction of heat through the roof via evapotranspiration of gained rainwater [2]; • habitat creation for plants and animals. When buildings are constructed, green zone is permanently destroyed. Green roofs are the way we can compensate the loss of green zone in the city by putting it back on the top of the building; • air pollution removal. Green roofs act as usual grass and clear air from particular matter by retaining it in the vegetation layer [3]; • decrease of urban heat effect. All cities more or less suffer from increased average annual temperature compared to their surroundings. This is mainly because of the albedo effect of construction materials which are used in the construction of buildings and streets. Other factors are industrial and technological processes emitting heat, reduction of wind speed etc. It is already proven that green roofs decrease urban heat effect because of better albedo and evapotranspiration [4]; • cityscape improvements. Green roofs can be used in urban planning as a way to green the cities and make the sight more esthetically attractive and relaxing to citizens [5]; • stormwater runoff retention. Green roofs can accumulate certain amounts of rainwater, thus (during heavy rainfalls) preventing it from surcharging the city`s sewage system and flooding streets nearby [6,7,8]. Additional benefits which have not yet been studied might include electromagnetic radiation screening and roof fireproof increase. In some countries there could also be financial benefits in the form of property and/or rainwater runoff tax and fee reductions. In any case, the effect that the presence of a green doi: 10.7250/iscect.2013.013