Coventry University green roof retrofit

Boughton’s Intensive green roof substrate has been successfully trialled in a ground-breaking analysis project at Coventry University assessing the feasibility of ‘greening’ landscapes with ecological beneficial habitats.

With the objective being to research the benefits and plausibility of incorporating green space and wildlife-friendly habitats into heavily built-up areas, Coventry University handpicked Boughton’s Intensive IN1 substrate based on its nutrient content, weight, and the inclusion of a water supply in chambers beneath the sub-base.

The majority of green roofs in the UK fall into the ‘extensive’ category and are based on a low growing succulent, Sedum, which only requires a few centimetres of substrate to grow, whilst intensive green roofs provide a deeper soil depth and can support a more complex plant system.

To this end, Coventry University wanted to explore the advantages of intensive green roofs, which offer greater biodiversity, often create accessible spaces, and offer the best insulation properties and storm water management. The organisation partnered with SEL Environmental, who provided its intelligent water management systems for the project.

Boughton’s Intensive IN1 substrate boasts greater organic content than extensive substrates, meaning it supports larger plants and can be installed at greater depths, varying from 100-500cm. IN1 provides a stable growing medium for wide variety of plants in intensive green roof installations, including green roof lawns, shrubs and trees.

Depending on the substrate depth and plant type, permanent irrigation systems (above or below ground) are sometimes installed with this substrate to as a backup for extended dry periods. They are not required for everyday irrigation, as the substrate has the ability to hold onto sufficient moisture during ambient conditions.

The project, funded by Knowledge Transfer Partnership (KTP) and headed up by Sophie Barron-West, followed plant growth for four years from 2017, with a break due to Covid 19. Dr Stephen Coupe and Dr Liz Trenchard from the University’s Centre for Agroecology, Water and Resilience (CAWR) offered their research expertise.

CAWR’s Dr Stephen Coupe says: “The technical requirements of Boughton IN1 were a big part of why we chose it. We also wanted the chance to get as many wildflowers in the space as possible. The nutrient levels were perfect because it wasn’t too rich. In fact, it was a ‘just right’ formulation that wasn’t going to overstimulate but would also deliver enough nutrients for what we needed. Ultimately it was going to be perfect for long-term sustainable plant growth.”

He continues: “Reliability was another consideration because we knew we could get it delivered on site on time and, because of Boughton’s location in Kettering, we weren’t concerned about lead times, so that was a plus. It’s safe to say it was a studied choice.”

Ground-breaking results

According to the University, the trial resulted in ground-breaking analysis into how different types of green roofs can be created and maintained, as well as what their benefits would be alongside others in a built-up area.

The project successfully demonstrated the ecological impact of placing retrofit green roofs onto existing infrastructure, even with a focus on wildflower species and a relatively short development time.

An independently-conducted ecological survey recorded five insect species that have national and local rarity value, including two species of bee that are deemed ‘nationally scarce’ and ‘nationally rare’. Of 457 preserved specimens taken on the green roofs at Coventry University, a total of 120 different insect species were recorded, including wasps, sawflies, hoverflies, beetles, and as many as 11 species of bee.

Coventry University’s findings revealed that the innovation in green roofs has improved and increased the total constructed habitat for rare insects. Research has also enabled better water management alongside habitat enhancement. This research has been incorporated into SEL’s product range, where green roofs are now used across four sites in Coventry, London, Aylesford and Blackburn.

CAWR’s Dr Stephen Coupe said: “Ecology, biodiversity and wildlife are largely forgotten by planners, designers and builders in developments. Most green roofs installed in the UK are based on sedum, and, while there are additional features that can be added to these green roofs to improve biodiversity, they are rarely incorporated. Our findings, using Boughton’s Intensive green roof substrate, are that the retrofit of green roofs is feasible and, more than four years into development, IN1 has supported verifiably diverse green roofs. The plants on these roofs supported several insects that have rarity status in the UK, which is very positive.”

Dr Coupe adds: “Whilst it is probable that substrates take many years to develop anything like the maturity comparable to natural soil, after just four years, IN1 went from having no recordable eukaryotes, to a concentration of organisms, including worms, soil mites and rotifers.”

Boughton Business Development Manager, Jason Lock comments: “Boughton was delighted to be part of this groundbreaking project and buoyed by such positive findings. Our products have been used successfully in a number of iconic green roof developments around the country over the years but it was a pleasure to be involved in such an important trial that would deliver verifiable results assessing the potential for green roofs to create new habitats in urban environments and enhancing local ecological diversity. Boughton offers an extensive range of green roof substrates and we welcome any research that helps further innovation around the application of green roofs.”

The experiment at Coventry University is ongoing and the team are set to feed back again at the end of the summer about how prolonged dry weather has affected results.

Dr Coupe says: “The beauty of this project is that there is no general timeline for a piece of green space. We need funding to support our ongoing investigations but there are options and opportunities for long-term research. It can last for the lifespan of the site and I think we will see really interesting developments. There is no reason why, over time, these green spaces would be indistinguishable from an existing habitat.”

Boughton’s portfolio of green roof substrates are specifically engineered for different types of roof greening, both for domestic and commercial projects. A full product specification is available for each of Boughton’s Green Roof Substrates, and other landscaping products, making exact specification simple and straightforward. There’s also a section on each product listed online, titled ‘to specify (copy & paste)’, designed to make your job even easier. 

To enquire about your next project, contact Boughton by calling (01536) 510515 or email sales@boughton.co.uk.