The Thermal and Rainwater Runoff Performance of an Extensive ...
The Thermal and Rainwater Runoff Performance of an Extensive ...
The Thermal and Rainwater Runoff Performance of an Extensive ...
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In summer, green ro<strong>of</strong>s c<strong>an</strong> retain 70–80% <strong>of</strong> rainfall <strong><strong>an</strong>d</strong> in winter they retain 10–35%depending on type <strong><strong>an</strong>d</strong> depth <strong>of</strong> substrate <strong><strong>an</strong>d</strong> type <strong>of</strong> vegetation [16]. During winter, there isgreater rainfall <strong><strong>an</strong>d</strong> less evapotr<strong>an</strong>spiration by the pl<strong>an</strong>ts because there is less growth.Overall, the deeper the substrate the greater the average <strong>an</strong>nual water retention. Intensivegreen ro<strong>of</strong>s with deeper substrates c<strong>an</strong> hold up to 20% <strong>of</strong> the rainfall absorbed for up to 2months [12].4.3 Climate Ch<strong>an</strong>ge Mitigation <strong><strong>an</strong>d</strong> AdaptionIn the UK, buildings are responsible for 45 percent <strong>of</strong> CO 2 emissions: 27% <strong>of</strong> the UK’semissions come from homes, 18% from non-residential buildings [17]. A high proportion <strong>of</strong>these emissions are from heating <strong><strong>an</strong>d</strong> cooling the internal environment. Reducing the energyconsumption <strong>of</strong> the UK’s buildings will reduce their contribution to climate ch<strong>an</strong>ge. <strong>The</strong>IPCC (Intergovernmental P<strong>an</strong>el on Climate Ch<strong>an</strong>ge) have said that buildings provide some <strong>of</strong>the greatest, most cost effective <strong><strong>an</strong>d</strong> fastest opportunities to tackle climate ch<strong>an</strong>ge. Greenro<strong>of</strong>s c<strong>an</strong> signific<strong>an</strong>tly reduce the cooling loads <strong>of</strong> buildings, resulting in reduced air coolingrequirements <strong><strong>an</strong>d</strong> therefore reduced energy consumption <strong><strong>an</strong>d</strong> the associated output <strong>of</strong>atmospheric carbon dioxide.<strong>The</strong> insulation levels required to meet current UK Building Regulations ensure that theinternal thermal perform<strong>an</strong>ce is largely isolated from external environmental conditions(ro<strong>of</strong>s should meet a maximum U-value <strong>of</strong> 0.16 W/m 2 K). <strong>The</strong>refore, the effect <strong>of</strong> green ro<strong>of</strong>son thermal insulation on new builds is negligible. When retr<strong>of</strong>itting a green ro<strong>of</strong>, green ro<strong>of</strong>materials should not be used as a substitute for insulation.Green ro<strong>of</strong>s c<strong>an</strong> also reduce the daily temperature fluctuations <strong>of</strong> building ro<strong>of</strong>s. <strong>The</strong> diurnaltemperature r<strong>an</strong>ge (the difference between minimum <strong><strong>an</strong>d</strong> maximum temperatures over a 24hour period) at the waterpro<strong>of</strong> layer <strong>of</strong> a green ro<strong>of</strong> is signific<strong>an</strong>tly less th<strong>an</strong> that <strong>of</strong> aconventional bitumen covered ro<strong>of</strong>; <strong><strong>an</strong>d</strong> is typically below 10 o C during the summer for <strong>an</strong>extensive green ro<strong>of</strong>. Some <strong>of</strong> the factors which affect the thermal properties <strong>of</strong> a green ro<strong>of</strong>include:Niall Carroll Page 31<strong>The</strong> <strong>The</strong>rmal <strong><strong>an</strong>d</strong> <strong>Rainwater</strong> <strong>Run<strong>of</strong>f</strong> <strong>Perform<strong>an</strong>ce</strong> <strong>of</strong> <strong>an</strong> <strong>Extensive</strong> Green Ro<strong>of</strong> System
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