Appraising the psychological benefits of green roofs for city residents and workers

Highlights

• Examines range of factors that influence psychological benefits of green roofs.

• Applies social-ecological and human-environment interaction frameworks for analysis.

• Identifies relevant physical, social, activity, and individual adaptation factors.

• Provides guidance for future research on psychological benefits of green roofs.

• Outlines principles for designing green roofs for psychological benefits.

Abstract

While a relatively small body of research links green roofs to psychological benefits such as aesthetic enjoyment and improved concentration, these outcomes are becoming important objectives in green roof design. Claims regarding benefits of green roofs are therefore often derived from research on psychological benefits of ground-level urban greenspaces. Compared with other urban landscapes, green roofs have limited space and accessibility, reducing the opportunity for physical exercise and the opportunity for larger masses of vegetation, particularly trees. Given these differences, there is a risk that the psychological benefits of green roofs are overstated or may only apply to a subset of green roof designs. Guidance for designing green roofs for psychological benefits may also be misleading if it fails to consider the unique green roof context. To address these challenges, we review research on psychological benefits of green roofs through a social-ecological lens on human-environment interactions. We consider how experiences of green roofs arise from an interaction between characteristics of the physical environment (including characteristics of green roof vegetation, wind patterns, and surrounding buildings), social climate (including social factors influencing access and use, and social norms for nature in cities), activities that can be undertaken on a green roof (such as exercise, socialisation, rest and relaxation), and individual resources and adaptation (for example, prior mood and opportunities to change environments to support individual needs). We explore how these factors interact with each other and with broader natural, built and socio-cultural systems that might encourage or inhibit opportunities to view, access, and enjoy green roofs. We conclude with recommendations regarding how green roofs can be designed to promote psychological benefits and identify future research needs.

Introduction

There is increasing awareness of the importance of urban nature for human well-being, with research demonstrating psychological benefits such as reduced stress and negative mood, improved attention control and renewed sense of vitality (Hartig et al., 2014). Consequently, urban greenspace design is becoming driven by goals of improving social and psychological outcomes for urban residents. This emphasis on psychological well-being is also evident for green roofs, where implementation may be motivated by potential benefits for nearby residents and workers in addition to the well recognised environmental benefits (Oberndorfer et al., 2007). While there is a significant body of research establishing how urban nature can promote psychological benefits (Hartig et al., 2014)– defined as changes in affect and cognition that are positively linked to well-being or function – there is reason to question whether these findings translate to the green roof context. Only a small body of research has directly considered the psychological benefits associated with green roofs, and generalisation of likely benefits from other contexts may not be appropriate given the significant differences in the ways people interact with green roofs compared with other forms of urban nature. While some green roofs clearly do promote psychological benefits (e.g. Lee et al., 2015; Mesimäki et al., 2019; White and Gatersleben, 2011), the circumstances under which this can occur are not well defined.

A considered appraisal of the psychological benefits of green roofs is needed because green roofs are a novel form of urban greenspace. Green roofs have existed in many different forms and across societies for long periods, and the benefits of green roofs for rainfall retention, reducing building energy use biodiversity and other ecosystem services are increasingly well understood (Lundholm and Williams, 2015; Williams et al., 2014). It is only relatively recently that they have been proposed as a way to ‘bring nature into cities’ for human benefit (see for example Loder, 2007). This understanding brings with it an expectation of the benefits to people long associated with parks and other forms of nature (Oberndorfer et al., 2007; Lee et al., 2015). Urban greenspaces have been linked not only to improved attention and mood, but to broader outcomes such as improved mental and physical health (Hartig et al., 2014), reduced aggression and crime (e.g. Kuo, 2003), improved productivity and creativity (e.g. Williams et al., 2018), and increased helping behaviours (e.g. Guéguen and Stefan, 2014). Although some have suggested green roofs will provide similar benefits (Oberndorfer et al., 2007), the ways that people experience green roofs may differ radically from the ways they typically experience parks and other ground-level landscapes. For example, while green roofs take many different forms, they are often not visible from ground level and visual access may be limited to people using the building the green roof is on or to those overlooking it (Sutton, 2014). Physical access can also be highly restricted, perhaps only to maintenance workers or to building users or to those with knowledge that the green roof exists (Yuen and Hien, 2005). Many green roofs are also relatively small, limiting the range of physical activities in which users can engage. Further, the types of ‘nature’ found on green roofs may be highly constrained by the size, environment or physical limitations of the roof. For example, the building weight-bearing capacity generally precludes planting of trees and shrubs (Weiler and Scholz-Barth, 2009). Research on psychological benefits of urban parks cannot therefore be simply generalised to green roofs.

We present a conceptual framework for analysing how green roofs can support psychological functioning in cities and apply this to review and reassess existing literature on the psychological and social dimensions of green roofs. The scope of our analysis includes a diverse range of green roofs, including extensive (lightweight green roofs with shallow substrates and low vegetation such as succulents) and intensive (roof gardens that require deeper soils and may include taller vegetation such as shrubs and trees) green roofs (Oberndorfer et al., 2007). Rather than treating these as separate types of green roofs, we consider how their physical and social attributes interact with the needs and actions of individuals in these environments and how these interactions could shape psychological experience. As the existing literature on psychological benefits of green roofs is very small, we first draw on psychological and social-ecological research to present a consolidated framework for analysing human interactions with green roofs. We use this framework to evaluate how psychological benefits of green roofs are influenced by the physical environment, social climate, activity and individual resources and adaptation. Through this integrated analysis, we suggest an approach to developing a more comprehensive and credible understanding of the psychological benefits of green roofs.