Bio diverse or Brown roofs are becoming ever popular in London and surrounding cities across the UK. Because they are a new roof type people often confuse what a bio diverse or brown roof is and also what it’s primary function is. Brown roofs have been created to best replicate habitats where a lot of building is takes place. With the increased levels of building many rare habitats are being replaced with large glass and concrete structures leaving what was once a haven for rare wildlife a redundant a grey stark blocks of land unusable for wildlife
We at eco green roofs look at bio diverse and brown roofs as a function to replicate the habitat which, was once at ground level at roof level. We use the word replicate for a couple of reasons many brown roofs were created using the demolition waste from the site and we would often here a term ‘site scrape’ which literally scrapes up the soil from the existing site. This method to create a bio diverse or brown roof is very dangerous due to the soil at ground level almost always containing contaminants such as asbestos and lead. This unscreened waste is dangerous to use and the olympic park had a few large areas of brown roofs replaced for this very reason.
We at Eco green roofs we best replicate the existing habitats with a range of green roof substrates and growing mediums. All of our green roof (brown roof) substrates are made of recycled material but this material is screened. We also use locally sourced material from various sites across the country to reduce any environmental impact.
Another key issue with a site scrape is there are often sharps (broken tiles and ceramics, nails, screws) within the scraped waste and this could potentially cause an issue with the roofing membrane.
When you first look at creating your brown roof you need to look at what functionality you need the bio diverse or brown roof to provide. by looking at the sites ecology report you can work out what wildlife had taken habitat on the site previously. This will usually include a list of native wildflowers, rare invertebrates, bats and birds that will need consideration in the brown or bio diverse roof.
With this list we can then create a specification to suit the brown roof. We can determine the depths required for the bio diverse or brown roof substrate (growing media.) Often like a brownfield site we use topography and undulate the substrates to create shading creating more bio diversity.
Some bio diverse or brown roofs are then plug planted and seeded with the native species found within the ecology report, some however are left to naturally colonise, the only issue with this depending on the height of the roof this may take some time to develop.
We have used many brown roof accessories to optimise the brown roof and maximise the bio diversity achieved. We often use logs on our brown roofs for beetles, sand piles and boulders for rare invertebrates and burrowing bats. Our brown roofs have had old tires, old rope and shingle to create many different areas and habitats across the brown roof (bio diverse roof.)
We always like to put a water source on our brown roofs to encourage birds to bath in them, this can be as simple as a dustbin lid upside down and half buried in the substrate.
Aesthetics of a Brown Roof
Bio diverse or brown roofs a often misconstrued to clients and they are unaware that ‘their green roof’ isn’t ‘green!’ a brown roofs main function is providing a habitat. That said a brown roof doesn’t have to look like an overgrown concrete tennis court. with some careful planning you can design an area that is fit for purpose but also performs as a bio diverse or brown roof should. We done this effectively at Westfield Stratford to this project in detail click the link below.