Positive Aspects of Green Roof Reducing Energy Consumption in Winter

Abstract

Greening structures attract worldwide attention because of their multidisciplinary benefits. Green roofs are considered one of the best ways to eliminate summer overheating, mitigate climate change, or reduce the urban heat island effect. The winter season and its impact on building energy consumption are often overlooked. Common standards do not take a green roof structure into consideration because of possible high water content in their layers. Additional roof layers may have a positive effect during the winter; they help reduce surface overcooling in cloudless winter nights. This paper analyses experimental measurements taken on two different extensive green roofs and compares the results with a single-ply roof (R) with a PVC membrane. Surface overcooling of the R due to radiation reaching up to 10 °C, whereas the green roof membrane is protected. The influence of thermal loss is not so important for the current climate in Central Europe, as the required U-values are lower than 0.1. The temperature difference is reduced from 17 °C on the membrane to 0.7 °C on the top of the concrete slab. The green roof is still advantageous, and the vegetation surface has better thermal stability. The advantage is clearly recognisable in the area of the condensation zone. The difference between these two extensive green roofs is very small in regard to the accuracy of the temperature sensors. The outcome showed the thermal loss reduction compared to the common flat roof; however, after analysis, it was more marginal than expected.

Environmentally Sustainable Green Roof Design for Energy Demand Reduction

“…A comparison of the two periods, namely summer and winter, shows that the increase in energy consumption in winter is only 10% of the total savings that can be achieved in summer. This is consistent with the limited amount of research that has investigated the thermal performance of green roofs in cold winter conditions [88][89][90][91]; in general, they found a moderate thermal advantage for green roofs in colder climates but a much smaller advantage in warmer climates.…”

Green roof evaluation and comparison during summer in Central Europe climate

“…There are two basic degradation factors of the waterproofing membrane on the flat roofs, which are the UV radiation and the temperature difference. Even the simple extensive green roof can stabilize the membrane temperature during winter, as it is shown in the outcomes from winter period in this research [4] or by the other authors [5]. Most green roof benefits are connected with the summer, such as reduction of the urban heat island intensity and summer overheating of interiors, rainwater retention and evapotranspiration, dust particles collection, fire safety, various architectural and aesthetic aspects, etc.…”

Increasing thermal protection with use of green roof

“…Similar research is conducted in the Czechs UCEEB with more types of green roofs [18]. With its new measuring platform of green roofs, the University of Zilina was added to the international effort to mitigate the climate change [19,20].…”