Following our controversial article covering a recent attack on green walls, UTS associate professor Sara Wilkinson looks at the good and bad of the technology.
Icelandic turf houses with green walls and roofs were the combined result of locally available building materials and a cold, harsh climate. Turf houses were, and are, well insulated buildings, providing good levels of thermal comfort.
In Norway, turf roofs are a traditional form of building construction and, from the Viking period and Middle Ages onwards were the norm, and not the exception.
It was only at the beginning of the 18th century in rural areas that tile roofs gradually superseded sod roofs. Corrugated iron and other industrial materials replaced these centuries-long traditional building materials and techniques. How short our memory is that we now perceive green walls and roofs as new technologies.
Yes, we can also argue that we have not used them here in Australia on a widespread basis, and so they are for many, something new and unknown.
With the new and unknown, as Robert Hughes labelled it, there is “the shock of the new”, and it is natural to be risk averse. However when we look around at those countries and places with experience, and listen to those with experience, we can relax, be reassured and be encouraged to learn new ways of doing things.
In response to this new technology, a group of experienced engineers, building surveyors, property managers, valuers and green roof and wall installers came together in 2016 to write a RICS Best Practice Guidance Note on Green Roofs and Green Walls.
This global guidance note, launched by the NSW Minister for Planning Rob Stokes in July 2016, covers all issues and aspects stakeholders need to consider in respect of due diligence when advising clients about green roofs and green walls. A comprehensive checklist ensures all technical and legal issues are covered.
One of the reasons we love green roofs and walls is their aesthetic. Having worked in Sydney Broadway for the last six years, opposite Central Park, I can say I have never seen so many people stop and look at a building.
They stop, they take photos – they can’t all be architects or landscape architects. These are ordinary people, who are literally stopped in their tracks by urban greening and nature. If this isn’t the biophilia effect in action; I don’t know what is. People have an affinity with nature; it’s part of being human.
3 reasons not to install green walls
Plants might wither or die
One reason you might choose not to have a green roof or wall is that plants might wither or die. Well yes, this is true and there are times when we get high winds and high temperatures that can affect plants; though with care usually they recover and flourish. There is a period when plants need to establish themselves and at times some may not flourish initially; when this occurs they may need to be replaced over time.
You could argue that “wilting” serves us with timely reminders of a changing climate and the effects of nature; it is a barometer. We need to take heed and adapt our behaviour to reduce our collective environmental impact. With innovations in technology, sensors exist that monitor moisture levels and temperature to ensure optimum watering occurs.
Another point to make here is that we do not routinely look at buildings and critique building defects (though I must admit as a chartered building surveyor I do!). When you walk down any street, and look at buildings closely, I can guarantee you will see defects; staining on parapets, cracked concrete sills and cracked mortar in brickwork, for example. It’s not particularly attractive, but we don’t call for the banning of these materials. Why not? Well, because over time, buildings age, sometimes materials weather and deteriorate and need maintenance and/or replacing. In this respect, we should use the same standards for assessment on all building materials, be they brick or plants.
Costs of maintenance
Reason number two is the cost of maintenance. There are a couple of ways to look at this argument. One is that installation and maintenance creates new employment opportunities for people. In the precarious world of the gig economy, new employment opportunity is something to be celebrated.
The second issue to consider is that, again, innovation in technology means that we can use “bots” to water, weed and seed plant beds. A horizontal bot, the “farmbot“, already exists and when a vertical version is developed, the OHS issues and costs of cradles on the elevations of buildings will no longer represent the only way to maintain an installation. Again, new employment is created in “bot” installation and maintenance.
The third reason not to is fire risk. I searched the web and academic journals, and asked academics and experts in green wall and green roof installation. The only evidence I could find of a green wall catching fire in Australia was in Redfern, at Arcadia Liquors in September 2012. A very small green wall, or vertical garden, containing a high number of plastic plants caught alight in a semi-enclosed beer garden. Apparently a guest lit a cigarette with a candle and set a fern alight. So an enclosed space and an unintended ignition. I found nothing before or after showing the incidence of fire in green walls.
Mark Paul, an experienced Sydney installer said plants and soil acted to dampen fire ignition.
Green walls are considered under the Alternate Solution consideration in the Building Code of Australia (BCA), which means designers have to show how the installation satisfies all aspects of the BCA, including fire safety.
Fire safety experts note green walls are a technology moving faster than prescriptive regulation, which leaves them to address the potential risks on a performance basis supported by available knowledge (research).
A 2012 US National Fire Protection Association research report on fire safety challenges of green buildings highlighted some potential risks and proposed mitigation strategies. The reported hazards imposed by vegetative covering (internal or external) related to:
- Ignition impacting evacuation
- Contribution to fire load
- Flame spread
- Impact of fire brigade operations
- Impact on smoke and heat venting
- Stability issues
Limitation of volume and the use of potting/hanging materials that limit the spread of fire is posited as the main mitigation strategy. Provided the volume and the materials used are controlled and maintenance plans are put in place, these hazards are considered moderate by the authors.
Nevertheless, quantifying acceptable volumetric extent and location of green walling in a building is the challenge (considering these days we see tall buildings with green walls running all along facades). More research is required to come up with a generic answer, but in the meantime; analysis of the risks on a case by case basis is a sensible approach.
Cities around the world turn to green infrastructure
In a 2018 Horticulture Innovation Australia funded report looking at whether mandatory or voluntary approaches to green roof and wall adoption would work best in Australia, we found Singapore had increased its coverage by 805 per cent from 2007 to 2017.
Toronto, with a mandatory approach to green roofs, increased covered by 360 per cent since a by-law was introduced in 2009. Many global cities are realising the need to remain attractive, liveable and desirable and that this can be achieved partly through making urban settlements as green and natural as possible.
Singapore realised in the 1980s that it needed to position itself as the “Garden City” as it would otherwise miss out on economic development and growth.
13 reasons why we should adopt green walls
- VOC reduction (new and old buildings).
- CO2/O regulation and carbon sequestration (indoor and outdoor applications).
- Opportunity for grey/blackwater filtering/processing (so much potable water is flushed in stormwater sewers, which could and should be reused in urban greening).
- Urban greening and biophilia (benefits to both host buildings and surrounding buildings gaining, gratis, visual access. Evidence of positive health impacts.
- Aesthetic improvement and increases to property value (internal and external applications with benefits extending to surrounding properties with virtually no floor space loss).
- Habitat production (needs to be generally inaccessible/undisturbed within the urban sphere). City of Sydney LGA has only four per cent remaining of indigenous flora and fauna; green walls are a great opportunity to reintroduce some species.
- Thermal insulation (internal and external benefits to surrounding properties). Experiments in Sydney showed a typical five-degree cooling effect of lightweight green roofs and walls, which would have been much appreciated in Penrith on 7 January 2018, when the temperature hit 47.3°C, making it the hottest place on Earth for the day. Widespread adoption of green roofs and walls is likely to mean less power outages in extreme hot weather as our aging infrastructure is less overloaded.
- Acoustic insulation (internal and external benefits to surrounding properties). With increasing urban densification, this is a very welcome attribute with positive health and wellbeing impacts.
- Reduced urban turbulence. The premise here is that wind forces are partially absorbed in green walls and some airborne pollutants are absorbed, improving air quality and reducing the wind tunnelling effect of urban canyons.
- Extended buildings facade life. The argument here is retrofitted vertical gardens protect facades from further weathering and deterioration.
- Improved hospital patient recovery and reduced post-surgery pain medication. Evidence is growing (pardon the pun) that access to greenery really does hasten recovery. Specifically there is a field (sorry!) of therapy, horticulture therapy, that has been shown to improve health and wellbeing in people in Sydney.
- Reduce urban heat-island (UHI) effect. A number of studies here and abroad have modelled the reductions in UHI possible from widespread adoption of green walls and green roofs.
- Urban food production – having locally grown fresh food reduces carbon food miles and shows, or reminds people, where food comes from. We owe it to the generations to come to show them how food can be grown, how long it takes to grow and what happens if it’s not watered properly. Clearly we can’t meet all our urban food demand but we can remind people what it looks like.
Having reviewed the arguments for and against green walls, for me, while we must be cognisant of and manage all risks, the arguments for adoption outweigh those against.
Dr Sara Wilkinson is associate professor at the School of the Built Environment, University of Technology Sydney.