The effectiveness of retrofitted green and cool roofs at reducing overheating in a naturally ventilated office in London: Direct and indirect effects in current and future climates

Abstract

Mitigating summertime overheating is increasingly viewed as a key issue in urban planning -a warming climate and increasing urbanisation will exacerbate the problem. The effectiveness of green and cool roofs at reducing summertime overheating was assessed for a naturally ventilated, poorly insulated office roof in London. This was contrasted to the application of retrofitting traditional insulation. The new Chartered Institute of Building Service Engineers overheating criteria was used to assess the level of overheating as predicted by a whole building thermal simulation model. The impacts of the roofing strategies were split into the direct and indirect effects. The indirect effects of the roofs were modelled using microclimatic modelling software. The results indicate the direct effects of green and cool roofs at reducing overheating are much greater than the indirect cooling effect. A non-insulated cool roof was found to be the most effective strategy. By insulating the roof, the level of overheating was slightly reduced. Non-insulated green and cool roofs were more effective than insulated roofs at reducing levels of overheating. When using a 2050 weather file, the building frequently overheated without the use of green or cool roof.

Maintaining Comfortable Summertime Indoor Temperatures by Means of Passive Design Measures to Mitigate the Urban Heat Island Effect—A Sensitivity Analysis for Residential Buildings in the City of Vienna

“…Green roofs reach surface temperatures of about 20-25 • C, compared to bitumen and gravel roofs with an average surface temperature of above 80 • C [25]. When looking at future climate scenarios, retrofitting roofs with green roofs can contribute to easing the effect of summertime overheating, as shown in [26]. In addition to the evaporative cooling effect caused by greened surfaces, plants support sound absorption and dust binding.…”

Influence of plant coverage on the total green roof energy balance and building energy consumption

“…Older buildings with poorly insulated roofs are expected to benefit more from green roofs than newer-built buildings with a higher level of insulation [11,[31][32][33]. To address the effects of green roof plant coverage on buildings with different levels of insulation, the DOE commercial reference building models for all three categories of new-construction, post-1980, and pre-1980 buildings [34] were used in this study.…”

“…Therefore, green roofs offer multiple benefits to cities from the water and energy flow perspectives. Urban-and building-scale benefits and positive effects of green roofs have been explored in several studies using numerical simulations, field measurements and laboratory experiments [9][10][11][12][13][14][15][16]. In their lifecycle, green roofs are not continuously fully-covered with plants resulting in heterogeneity along the green roof surfaces.…”

Urban heat island modelling of a tropical city: case of Kuala Lumpur

“…Such fast, local-scale modelling tools have been widely used in the last decades to calculate temperature perturbations in mid-latitudes from city to neighbourhood/street level with the aim of studying the extent and spatiotemporal variation of UHI to help identify risk factors within a given urban context and to test the effectiveness of possible land-use change or mitigation scenarios (e.g. Jacobson and ten Hoeve 2012; Virk et al 2014Virk et al , 2015, but their customisation for use to model (sub)tropical cities has not been achieved.…”