G r e e n R o o f s a s P a s s i v e C o o l i n g S t r a t e g i e s
589
GREEN ROOFS AS PASSIVE COOLING STRATEGIES UNDER
TEMPERATE CLIMATES
Marco D’Orazio
1
& Costanzo Di Perna
2
& Elisa Di Giuseppe
1
1
Construction, Civil Engineering and Architecture Department, Faculty of Engineering, Marche Polytechnic
University, Italy,
2
Industrial Engineering and Mathematics Sciences Department, Faculty of Engineering, Marche Polytechnic
University, Italy,
Abstract
The research aims to the comprehension of the energy performance of a green roof,
also compared to other passive cooling strategies, when realized on slabs with very low
thermal transmittance, as imposed by recent laws on the energy performance of
buildings also in Temperate Climates.
Although many studies in literature highlight the potential of green roofs on the
improvement of internal conditions (reduction of incoming heat fluxes, thermal wave
phase shift), knowledge regarding the use of these technologies in highly insulated
structures is quite limited.
All EU countries in particular, following the issuing of two important Directives (“Save”
and “Nearly Zero Energy Buildings”), are enacting decrees which have placed regulatory
requirements and strict limits to the thermal transmittance of building components.
If the “overinsulation” strategy in Temperate Climates (i.e. Italy, Greece, Spain), is useful
for the winter energy savings, it risks to limits the effectiveness of alternative passive
cooling strategies, as the use of green roofs.
We carried out a thermal monitoring of seven low U-value roof systems, differentiated by
the type of covering, the type of slab, the presence of a ventilated cavity, the presence of
a vegetated substrate.
Experimental results show that the green roof and the other passive cooling technologies
benefits, as the reduction of the incoming heat flux and internal surface temperatures,
are quite limited by the roofs high insulation imposed by actual laws, which consider the
overinsulation as the whole strategy for energy saving even in Temperate Climates.
Keywords:
Green Roof, Insulation, Temperate Climate, Case Study, Passive Cooling.
Introduction
Even though numerous studies agree on the overall efficiency of a green roof, our
knowledge about its performance on highly insulated buildings is still limited.
In fact, in order to reduce CO2 emissions into the atmosphere, following the Kyoto
protocol, many countries have introduced specific laws that focus on reducing energy
consumption in the construction industry, as it is 30–40% responsible for total energy
consumption. In EU countries specially, two directives have been issued that have
obligated the EU member states to come up with specific laws (“Save” and “Nearly Zero
Energy Buildings”).
As such, in the past few years, a high demand has arisen for insulation of building
envelope in the construction industry in order to reduce energy consumption in winter.
On the other hand, till date, measures regarding improving the performance of buildings
in the summer season under warm and temperate climates are still lacking.
Plus, there is no standard regulation that planners can refer to, a regulation that is able
to precisely define stationary and periodic thermal transmittance of green roofs.
