Green roofs have gained great attention of urban planners and architects recently due to some obvious benefits such as aesthetic value and increased biodiversity and improved microclimate conditions in cities by reducing the heat island effect.
It is clear however that we need to move green roof design based mostly on aesthetic performance in to designing green roofs to match required performances so urban planners and architects can use them to their full potential.
KEY PERFORMANCE INDICATORS OF GREEN ROOFS
There are four key performance indicators of green roofs that are important tools for urban planners, municipalities and architects to manage not only building project, but also their energy and water policies.
- Energy performance of green roofs in summer (cooling effect)
- Energy performance of green roofs in winter (thermal insulation)
- Rainwater or stormwater management performance
- Performance in reducing the heat island effect
The performance of these key indicators can be objectively measured. However, one needs to keep in mind there are a lot of factors that can influence the performance of sedum based vegetative roofs.
- type of Green Roof (thickness and type of growing media, type of drainage, type of plants)
- type of building construction (metal, wooden, concrete) and design of the roof (what kind of insulation is used, what kind of water proofing,..) and
- additional aspects such as climate conditions, additional irrigation or not, as well as condition in the building itself (average temperatures in the building)
Elements effecting real performance of Green Roofs
So considering all above, simply saying 25% or 75% saving of energy and 90% rainwater retention (which is to often the case) can be misleading and can often causes disappointment when optimistic figures are not reached.
UNDERSTANDING REAL PERFORMANCE OF GREEN ROOFS
Lack of real performance understanding was also one of the main reasons on why Urbanscape decided to cooperate with the Faculty of Mechanical Engineering, University of Ljubljana, Slovenia, to perform multi- year study on “Thermal and hydrological response of green roofs in different climatic conditions”…
The results have been used to prepare special software package “Urbanscape® Performance Evaluation Tool” or simply PET”. The PET helps current and potential users/owners of extensive green roofs understand the real performance they can expect from their green roof.
The numerical data calculated by PET have been several times in-situ evaluated to grant accuracy. Real life testing is still going on in order to even improve the accuracy of the tool that is currently already in use.
URBANSCAPE® PERFORMANCE EVALUATION TOOL USAGE AND REPORTS
The Urbanscape® PET software package is simple to use. It requires a 3-step user input:
- Definition of building construction, roof type, outer surface optical properties of the roof
- Definition of Green Roof layer components, composition, thickness and irrigation scenario.
- Selection of site meteorological parameters and definition of mean in-house temperatures of specific building during different periods (winter – during the heating season and summer – during the cooling season)
The results are then presented in a simple report and cover the 4 key performance indicators:
- Cooling effect and energy saving in summer due to less air-conditioning needed
- Thermal insulation effect and energy saving in winter due to lower energy transfer through the roof.
- Rainwater management control data including water retention in the green roof and yearly / monthly run-off data (all based on real climate conditions)
- Temperatures on top of the Green Roofs vs regular roofs (positive effect on UHI)
The results are presented in the form of graphs with hourly, monthly, seasonal and yearly values of calculated parameters comparing performance of building with installed Green Roof vs. same building w.o. installed green roof.
In the following weeks we will cover each of the key performance indicators more in depth and give you some practical examples of how the performance of a specific roof was calculated with the PET tool.
If you are interested in receiving a sample Performance evaluation report for a selected town / country, please click here: