Planting Green Roofs and Living Walls

About this book

The idea that buildings should be clothed in living plants is ancient — rooftop gardens appear in accounts of Babylon, and vine-covered walls have sheltered Mediterranean courtyards for millennia. But the systematic study of designed green roofs and living wall systems as performance-driven components of contemporary architecture and urban infrastructure is a relatively recent development, emerging from the convergence of ecological research, building physics, horticulture, and sustainability policy in the late twentieth century. Planting Green Roofs and Living Walls, revised and updated edition, by Nigel Dunnett and Noël Kingsbury, published by Timber Press in 2008, is the authoritative English-language reference that synthesises this interdisciplinary knowledge into a coherent and practical guide for designers, builders, landscape architects, and horticulturalists.

Dunnett and Kingsbury approach the subject with complementary expertise: Dunnett brings deep knowledge of plant ecology, urban greening research, and designed plant communities, while Kingsbury contributes extensive experience in naturalistic planting design and horticultural practice. Together they cover both the technical infrastructure of green roof and living wall systems and the botanical and design principles that determine how well those systems perform and how they appear over time. The revised edition, appearing four years after the original 2004 publication, incorporates a substantially expanded case study portfolio, updated technical guidance reflecting advances in substrate technology and membrane design, and new material on living wall systems that had developed significantly in the intervening period.

The book distinguishes clearly between the two fundamental types of green roof, whose different characteristics suit them to very different applications. Extensive green roofs are characterised by shallow substrate depths, typically between 20 and 150 millimetres, and by plant communities composed predominantly of drought-tolerant, low-growing species — sedums, sempervivums, native wildflowers, and drought-adapted grasses — that can survive without supplementary irrigation once established. Their lightweight construction, typically adding between 60 and 150 kilograms per square metre when saturated, makes them suitable for retrofitting onto existing buildings whose structural capacity was not designed for heavy roof loads.

Extensive roofs are designed to be largely self-sustaining, requiring only minimal maintenance — occasional weeding, inspection of drainage outlets, and periodic fertiliser application — making them economically attractive for commercial and industrial buildings where ongoing maintenance costs must be controlled. Intensive green roofs support a far greater diversity of plant material, from lawns and perennial borders to shrubs and even small trees, within substrate depths that may range from 200 millimetres to over a metre. The additional growing medium depth supports a wider root system and higher moisture retention, making irrigation generally necessary during dry periods.

The structural load of an intensive roof in saturated conditions can exceed 700 kilograms per square metre, requiring purpose-designed or reinforced structural support. In return for these greater demands, intensive green roofs offer the full range of landscape design possibilities — creating usable rooftop gardens, biodiversity habitats, amenity spaces for building occupants, and urban food growing areas. They are particularly associated with prestigious commercial developments, public buildings, and high-specification residential projects where the landscape quality of the roof is a programmatic requirement.

Dunnett and Kingsbury give substantial attention to the performance benefits that both roof types deliver, grounding their discussion in the growing body of quantitative research available at the time of writing. Green roofs significantly attenuate stormwater runoff by absorbing rainfall into the substrate and releasing it through evapotranspiration, reducing both peak flows and total volumes discharged to urban drainage systems. Depending on substrate depth and seasonal conditions, retention rates of 50 to 90 percent of annual rainfall have been documented for extensive roofs in temperate climates.

The thermal mass of the saturated substrate and the insulating properties of the growing medium reduce both heat gain in summer and heat loss in winter, improving building energy performance. The substrate and plant layer protect waterproofing membranes from ultraviolet degradation, thermal cycling, and physical damage, substantially extending membrane service life and reducing lifecycle replacement costs. The ecological dimension receives careful treatment throughout the book.

Green roofs, particularly extensive roofs with diverse native plant communities, can provide valuable habitat for invertebrates, birds, and other urban wildlife. Research conducted at installations in Switzerland, Germany, and the United Kingdom documented green roofs supporting assemblages of rare and specialised invertebrate species — notably ground beetles and spiders — that are largely absent from conventional urban surfaces. Dunnett and Kingsbury provide guidance on designing plant communities to maximise biodiversity value, discussing the relative merits of locally sourced native species versus hardy horticultural varieties, and the importance of substrate heterogeneity in supporting diverse invertebrate communities.

Living wall systems — vertical surfaces covered with plants rooted either in panels of growing medium or in hydroponic systems fed by nutrient solution — receive expanded coverage in the revised edition. The book addresses both the structural requirements of wall-mounted systems and the distinctive horticultural challenges of growing plants on vertical surfaces, where gravity-driven moisture distribution, exposure to drying winds, and limited root volume create demanding conditions that differ substantially from conventional planting situations. Plant selection for living walls must prioritise species capable of tolerating these conditions while delivering the intended visual and ecological effects.

For the green building community, this book provides both the technical foundation and the design vocabulary to specify, implement, and maintain green roof and living wall systems effectively — understanding them not as decorative additions but as integral components of high-performance, ecologically responsive buildings.