Living roofs are becoming more and more common in cities due to the large range of benefits they bring. Now with the introduction of the new UK green roof substrate test methods, STRI technology manager, Dr Tom Young, discusses the benefits to the industry.
In early June STRI announced the release of the new ‘BSI 8616 code for the Specification for performance parameters and test methods for green roof substrates’, which is a bit of a mouthful.
In a nutshell, this is the UK’s first set of dedicated green roof substrate test methods. It also provides detailed substrate guidelines for extensive green roofs. It was developed by STRI working closely with the University of East London’s SRI Group, the British Standards Institute (BSI) and other partners.
STRI’s green roof substrate testing facility is currently the only laboratory in the world to offer complete green roof substrate testing and analysis according to the BS 8616 standard.
Building designers and city planners are now utilising vegetation (green infrastructure) to improve not just the aesthetics of a building, but also the environment in and around the building by removing air pollution, reducing noise, cooling the air and reducing the amount of rainwater runoff.
Although vegetation provides the ‘green’ part of a green roof, the real workhorse of a green roof system is the substrate, or growing media. This is an engineered soil designed to fulfil several functions, including providing a growing media for vegetation to successfully grow in for a long period of time. Other characteristics a good substrate should have are:
- Light weight in order to reduce weight loading on the roof
- Hold sufficient water for plant growth but also allow sufficient water to infiltrate to prevent ponding on the roof
- Low in nutrition to prevent excessive vegetation growth but enough nutrition to maintain healthy longterm vegetation
- Possess no phytotoxic material that can harm plant growth or end up in rain runoff
- Maintain good porosity, even under wet conditions
- Possess the correct chemical properties for the intended vegetation
- Possess the ability to ‘wick’ water if a subsurface irrigation system has been installed
Green roof substrates have a lot of tasks to perform, but if not designed correctly they will be unsuitable for a green roof.
Green roofs can also differ quite drastically in their depth, vegetation type, climate and even slope. Therefore, different substrates are appropriate for different situations.
Consequently, laboratory testing is important for selecting the most appropriate substrate and to also check if the substrate meets basic requirements. However, in order for laboratory testing to be useful for a whole industry a consistent approach in testing methods must be used if results are to be easily compared. If different methods are used, different results for the same substrate can be obtained.
Previously the UK did not have a unified set of dedicated green roof substrate test methods and relied on using test methods from other countries and other industries.
The new ‘BSI 8616 code for the Specification for performance parameters and test methods for green roof substrates’ is the first set of dedicated green roof test methods for the UK and will allow a consistent approach to be taken when assessing green roof substrate.
The standard also has substrate property guidelines for designers to specify against, although it is important to understand that not all substrates are the same and sometime a substrate may be outside of these normal guidelines for a good reason.
This is an exciting development for the green roof industry as well as for STRI who is expanding its involvement in the green infrastructure market, bringing expertise from many of our existing disciplines including substrate testing and design, landscape architecture and sustainable urban drainage design.
The BS 8616:2019 (Specification for performance parameters and test methods for green roof substrates) is available on the BSI and BSOL shop accessible here.
Contact Dr Tom Young for help and advice with green roof substrate testing or research on Twitter, call +44 (0) 1274 565131 or email firstname.lastname@example.org.