Ivan Clark, our Placemaking Team Manager at SNH, tells us about a partnership project exploring the contribution that green roofs can make to successful, climate-resilient places. He found that by applying the right kind of roof to the right building in the right place, green roofs can be a cost-effective way of helping cities adapt to the impacts of climate change, supporting the health and well-being of Scotland’s communities and providing habitats for wildlife…
In a recent response to a Scottish Government request for advice on a ‘green recovery’ from Covid-19, the UK Climate Change Committee suggested, among other things, “supporting the green roof and sustainable drainage industries to help to bolster Scotland’s adaptation services sector.” This is to be welcomed, because although green roofs are commonplace in London and in much of Europe, there is very little use of Green Roof Infrastructure in Scotland, particularly in housing developments. A previous SNH Commissioned Report, Maximising the Benefits of Green Infrastructure in Social Housing, suggested that this was due to a lack of awareness of the benefits of green roofs, the need for a persuasive ‘business case’ and the assumption by some developers that the cost of green roofs could threaten development viability.
To address these perceptions, Scottish Natural Heritage has been working with City of Edinburgh Council and others to explore the viability of integrating green roofs into an existing development proposal. The Meadowbank Development Green Roof Options appraisal was the result of a partnership between the Scottish Government, Architecture and Design Scotland, the Scottish Federation of Housing Associations and City of Edinburgh Council.
The partners commissioned a highly-skilled and multi-disciplinary design team (comprising Architects, Landscape Architects, Structural Engineers, Quantity Surveyors and a leading UK Green Roof expert) to carry out a viability study based on an existing public interest led housing and mixed-use development proposal at Meadowbank, close to the centre of Edinburgh. The team took a collaborative place-based approach to exploring the solutions most appropriate to the specific challenges and opportunities at the site.
Having agreed the types of roof solutions that would provide the most benefits, the costs were calculated and the proposals refined. In terms of the ‘business case’, the report considered the role of the blue-green roofs in attenuating the flow of surface water and the implications of this for the use of land and the need for other grey infrastructure. It also looked at the likely energy savings from the green roofs over the long term.
Green roofs at the Meadowbank site would help create an exemplar nature-rich development in the centre of Scotland’s capital city: Meadowbank is within a short flight of other pollinator habitat at Holyrood Park and the Scottish Parliament.
Green roofs would support the health and well-being of residents and provide benefits to the wider community that would use the site: Some of the green roofs could add value to potential community facilities such as nurseries and GP surgeries.
Green-blue roofs reduce the need for other grey infrastructure: Introducing green roofs across the site could result in a 38% reduction in the rate of surface water run-off. Along with other SUDs features, this could allow the removal of the need for below ground treatments (tanks and pipework) and reduce potential interference with contaminated land.
Green-blue roofs allow for more efficient use of land in constrained urban sites. Based on an average density of housing across the whole site of 110 dwellings/ ha, the space required for a ‘traditional’ SUDs pond, large enough to provide similar levels of attenuation provided by the blue-green roofs, would equate to around 40 dwellings per hectare.
Initial capital costs of green roofs are modest compared to overall capital costs of the development: The use of green roofs compared to traditional roofs represented an estimated uplift in overall construction costs for the whole development of less than 0.25%. If the additional capital costs of the roofs were split between all the dwellings at the site, the costs would equate to around £350 per dwelling. Based on their increased longevity and contribution to energy efficiency (insulating in winter and cooling in summer) the ‘payback’ period was estimated to be between 6 and 20 years.
Note: The options appraisal is based on a development proposal currently (as of May 2020) subject to a separate live planning application. The current application does not require roof types to be specified but in light of this report, City of Edinburgh Council will consider how green roofs could be incorporated at the next stage.