Topic 3 Taxonomies of green roofs based on general environmental conditions
Some studies have examined how different climates influence the performance of green roofs, as well as which type of green roof is best suited for specific climates…
Study 4 compared an intensive and an extensive green roof during a prolonged storm period, examining their capacity for water retention (Stefannoff, 2019) . The reports were:
- Extensive roof was able to reach 20% volumetric water capacity.
- Intensive roof was able to reach 25% volumetric water capacity.
- Volume of outflow was higher in an intensive roof compared to an extensive one.
This suggests that intensive roofs have higher capacity to retain water, but the difference with extensive ones is minimal.
Study 5 examined the impact of an extensive green roof on a building’s energy performance in France (Jaffal, Ouldboukhitine and Belarbi, 2012).
- They reported that there was a decrease in the annual energy demand in the range of 6%.
In the summertime,
- The roof slab temperature was reduced by about 30 °C.
- The roof cooling effect was three times more efficient than an ordinary roof.
- The indoor air temperature was decreased by 2 °C.
In the wintertime, the green roof reduced heat losses during cold days but increased them during the sunny days of the winter.
Study 6 examined the heat flux of an extensive green roof and related it to solar radiation, substrate temperature and snow depth (Lundholm, Weddle and MacIvor, 2014) . They reported the following:
- There was lower heat loss in the green rather than conventional roof.
- The benefits of green relative to conventional roofs were lower in extreme winter conditions.
- Plant species on the green roof affected depth and duration of snow coverage.
They conclude that the net thermal benefits of green roofs in wintertime depend on climate, plant choice, roof construction and location.
Study 7 assessed the performance of an extensive green roof during two periods in wintertime, one with a snow cover and one without (Zhao et al., 2015). They reported the following:
- Green roofs reduced the heat flow through the roof and thus reduce energy demand throughout the winter.
- Under snow cover, the thermal resistance of the green roof was reduced and thus energy savings were condensed also.
This suggests that while an extensive green roof reduces heat flow and energy demand during wintertime, this ability is condensed during snow cover.
Study 8 (Collins et al., 2019) asserted the findings presented by study 7 and study 6. Study 8 found that:
During major freezing periods, there was a decrease in heat flux for the green roof.
The continuous decrease in temperatures however led to the accumulation of snow on the green roof and a reduction to its ability to moderate heat flux.
