Substrate Depth, Vegetation and Irrigation Affect Green Roof Thermal Performance in a Mediterranean Type Climate

Abstract

Green roofs are consistently being used to reduce some of the negative environmental impacts of cities. The increasing interest in extensive green roofs requires refined studies on their design and operation, and on the effects of their relevant parameters on green roof thermal performance. The effects of two design parameters, substrate thickness (ST) and conductivity of dry soil (CDS), and four operating parameters, leaf area index (LAI), leaf reflectivity (LR), stomatal resistance (SR), and moisture content (MC), were investigated using the green roof computer model developed by Sailor in 2008. The computer simulations showed that among the operating parameters, LAI has the largest effects on thermal performance while CDS is a more influential design parameter than ST. Experimental investigations of non-vegetated and sparsely vegetated green roofs in Melbourne were principally used to understand the effect of the substrate and enable better understanding of dominant heat transfer mechanisms involved. Investigated green roofs had three substrate thicknesses (100, 150 and 200 mm), and their performance was compared to a bare conventional roof. In contrast to the computer simulations, the experimental results for summer and winter showed the importance of MC and ST in reducing the substrate temperature and heat flux through the green roof.

Experimental Winter Monitoring of a Light-Weight Green Roof Assembly for Building Retrofit

“…In their study in Toronto, Liu et al [38] also observed a similar effect due to heat loss reduction. Overall, the obtained results were discreet due to the high insulation of the building [25,26], to the relatively early stage of the vegetation development, and the winter season when in general, fewer differences can be observed [24].…”

“…The proper specification is essential for designing an effective system. Local boundary conditions such as air temperature, relative humidity, incoming solar radiation, rain incidence, and of course the overall stratigraphy, and materials contribute to the thermal transmittance of the construction skin, and play a crucial role for the effectiveness of the roof [3,24]. Some authors discuss that for highly insulated buildings and low heating demand, the thermal effects of the green roofs are not relevant [5,7,25,26].…”

Viability of Green Roofs as a Flood Mitigation Element in the Central Region of Chile

“…On the one hand, the total runoff volume will be largely determined by the total amount and intensity of precipitation. On the other hand, many studies agree that the soil type and its properties, including the type of vegetation, has a greater influence on green roof water retention capacity [41,42,51]. In this sense, the type of vegetation commercially available for non-intensive green roofs is very limited, with grass or sedum being practically the only commercial options.…”

Investigating Thermal Performance of Residential Buildings in Marmari Region, South Evia, Greece

“…In terms of the design and operational conditions of green roofs, experimental investigations unveiled that the operating parameter of moisture content and the designing parameter of substrate thickness reduce the substrate temperature and heat flux through the green roof, thus, consistently reducing some of the negative environmental impacts of built environments [59], generating considerable energy savings, improving the thermal performances of buildings, as well as substantially improving the dynamic properties of traditional roof structures, especially in the case of roofs with limited dynamic performances [60].…”