The increasing popularity of green façades, living and brown walls comes under scrutiny in the first of a three part series.
This time we clarify some core concepts and terminology, ahead of an exploration of systems available and their likely benefits.
Opportunities for façade greeningAccording to the United Nations forecast, 70% of the world population will be living in cities by 2050 (UNFPA 2007). Such a major shift away from rural and naturally vegetated areas to the polluted, noisy, and crowded concrete jungle of modern cities is and will continue to be profound. We must find new and innovative ways to better integrate nature into our ever expanding cities. Green roofs and parks are one way to do this but there are substantial amounts of vertical space that for the most part have been under-utilized. Green walls not only bring nature back into city life, they do so in a way that is accessible to everyone
In 2010 the Government Office for Science published the 'Foresight Land Use Futures Project'. Set against a background of commercial pressures for increased land use and development this document, and the Landscape Institute (LI) in their publication 'Green infrastructure', describe the benefits of a more integrated approach to the broader issues of housing, flood management, food production and biodiversity. While such issues are often viewed in isolation; these documents state that a more dynamic, coordinated approach offers many benefits and needs to be taken seriously.
The LI states that Green infrastructure (GI) covers everything from managed coastal and upland areas, wildlife habitats, agriculture, timber production, the connecting green spines of waterways, woodland, green spaces including parks; these resources contribute to social cohesion, delivering significant benefits to the economy. In an urban setting GI offers boulevards, plazas, trees and green space, green roofs and walls, that link wildlife and people to this bigger picture.
The technology for green roofs is now established and commonplace – the direct environmental benefits, well documented. façade greening is catching up and is one of the fastest growing areas of the green technology industry. Germany is at the forefront of this development due to decades of state sponsorship and a targeted sustainability policy across its economy. Use of green technology (for example, green roofs, façades and permeable pavements) is incentivized in Germany. Roof greening, via planning acts in place since 2010, is now a way of reducing sewage charges for a building owner. There are at least 800 articles and documents in German covering façade greening along with newly emerging technical standards.
Brandwein (2015) states that there are large untapped resources of vertical wall available in dense cities ready for greening and of value where ground space is earmarked for more commercial purposes. Controversially, in his 'Biotope City', he talks of biodiversity (the variation of animal and plant species) being higher in cities now than the surrounding countryside. While an extreme argument it is clear that, with the continued expansion and densification of cities and rapid decrease in wildlife, cities need to play an ever increasing role and arguably in light of the above government thinking, mitigate the impacts they make by ensuring sustainable expansion.
According to the International Union for Conservation of Nature (IUCN) there are greater than 73,600 species on the red list of threatened species with numbers of plants, animals and fungi facing extinction – degradation of habitat is a significant cause. In the UK, organizations such as the Joint Nature Conservation Committee (JNCC) provide evidence of pressures on habitats and species – they point to habitat decline in the UK having the largest impact on biodiversity loss in our four nations. Brandwein argues that the city is part of nature, like any other habitat, and that the assimilation of man and nature will form part of a new language of aesthetic expression; he states that:
'Nature has reached the limits of resilience as demonstrated by such phenomena as climate change and the rapid loss of biodiversity... The organic world must be integrated into the design of buildings as a self-evident element. The rationale of the modern city will then achieve a new additional dimension: green as an equal element of design alongside stone, steel, wood and concrete.'
Clearly façade greening has a role to play as an efficient method for improving biodiversity in urbanity. Additional beneficial claims for 'greened' buildings include an ability to reduce pollution and improve air quality, provide sound attenuation, enhance thermal performance, enable energy saving and promote life cycle benefits. However some façade greening systems can be tricky to install and maintain correctly. As research is pointing to their greater value and use what are the impacts and how sustainable are they? This series of articles is intended to shed some light on these claims and questions. To promote precision, it is necessary to begin with some clarification on terminology.
Types of façade greening
Façade greening is primarily proprietary in nature with installation and ongoing maintenance often installed as a package by one manufacturer/ supplier. There are a range of terms in use which the reader may find baffling and sometimes contradictory. Therefore, for clarity, vertical greening can generally be classified into three main strands:
- 'Green façade systems': where climbing plants and vines are rooted in the ground or elevated planter boxes – these are grown vertically directly onto the façade (extensive) or separately on trellis work (semi-intensive).
- 'Living wall systems': where plants are artificially supported ('intensive' – using growing media, artificial substrates, irrigation systems or hydroponics). This is where manufacturers/ designers use a range of supporting material, Ottele (2011) breaks this down into:
- Planter troughs, modular pocketed panels.
- Foam substrate.
- Layers of felt sheeting.
- Mineral wool.
- 'Brown wall systems': an addition by the author, these are naturally self-seeded wild plants that find a crevice or other root hold along building façades – this could be an accidental or intentional design feature.
Furthermore, it is a generally held misconception that plants, more specifically their roots, cause damage to a building façade. There are instances where this can occur and, according to Ottele, this is worst when rooting finds its way into vulnerable fabric such as cracked bricks, mortar or friable stonework. Climbers can also find their way (up to seven metres) through dark cavities and other gaps around buildings. Due to this concern, vertical greening, can permit plant growth either by:
- Attachment to the building façade material, referred to as direct greening; or by
- Separation from the façade using a supporting framework or system, referred to as indirect greening.
Selection of one system over another may depend on the client brief or a vital appearance to the planted wall. Requirements can be driven by a particular need for the wall to look very lush for example, in such a case water loving plants, bedded in a felt wall may be the best solution. In another instance costs may be the driver and a green façade may offer an economic solution. Choice of plants and the systems that support them are not mutually exclusive, rather they need to be considered against a range of criteria. We'll look at these criteria in subsequent parts.
Next: Part Two: Systems
The next part in this series offers further detail on the different façade greening systems available, with technical guidance covering aspects such as plant selection, health, irrigation, structural considerations and maintenance.
References made across the whole series are listed below: