Southwest Environmental Limited

Bio-Diverse Living Roof Specification

Given time it is likely you yourself could write a living or green roof specification, and draw (pens and paper) a plan to describe your proposed living or green roof, to planners. But many will not have the time, or perhaps the inclination to do this. If you do then please follow the below guidance and we wish you luck and good success. If you would like SWEL do do the paper work for you we would be happy to provide a quotation for doing so.

Different Types of Living Roof

Roofs aimed at replacing or replicating habitats are becoming more common in the UK. These roofs are sometimes referred to as: biodiverse; brown; rubble; brownfield; eco; habitat or even by the name of the species they are aimed at i.e. black redstart roof.

Common to any green roof:

• A building structure designed to take the loads of the proposed green roof
• Root resistant waterproof membrane or roofing finish
• Suitable drainage system to allow excess water to leave the roof easily
• 300mm gravel or paving un-vegetated margin to all upstands and roof penetrations
• Upstands of a suitable height to prevent material being blown off the roof
• There should be a 1m wide, 300mm tall un-vegetated barrier every 40m on large areas of green roof
• Growing medium should be not more than 20% organic mater by volume

The aim of a biodiverse roof is to replicate as far as is practical the ecological requirements for the local area. The natural habitats created are designed to support a variety of plants, birds, animals and invertebrates. The careful design and construction of these habitats is key to conforming to the local Biodiversity Action Plan (BAP).

Green Specification Roofs for Insects, Bugs or Invertebrates

Buglife publish an excellent guide on the specification of green roofs or living roofs to encourage invertebrates. The roof should be considered from early stages of project as it will have structural and design implications. There has been a trend for the installation of sedum roofs which are typically "extensive" in nature. These are thin substrates planted with drought tolerant succulent plants.

A thin substrate restricts the diversity of the plants one can incorporate on a roof. "Normal Plants" such as grasses may not grow on an extensive room with a thin substrate, and as such you are limited to sedums. The resulting lack of plant diversity and habitat diversity means that these systems do not constitute a bio-diverse roof.

The creation of habitats, the addition of habitat features and management can maximise the potential of bio-diverse roofs to support invertebrates and other wildlife such as birds. Many other factors, including the roof angle, aspect, size and height, will also have an influence and should be taken into consideration. Inclusion of bug hotels is another trick to boost surface area.

Should I Include Sedum on a Bio-Diverse Living Roof

The inclusion of Sedum plants on a bio-diverse roof can be useful – but should normally comprise no more than 30% of the species composition. There is some anecdotal evidence that drought tolerant Sedum species and other succulents can aid the establishment of wildflowers.

How to You Layout a Living Roof

There are lots of living roof  layouts that you can choose from. Typically they all incorporate some form of unplanted area, these serve a useful purpose for ecological purposes and also give a walk way for maintenance etc. The layout will large depend on you preferences, it may be dictated by roof top infrastructure such as roof lights or ventilation ducting.

Solar Panels on Living Roofs

It is a very common situation to have both a living roof and solar panels. The problem is that solar panels mounted low down to avoid visual impact, coupled with a green roof / living roof planted with shrubs is not a happy union. Often upon visiting a roof after a number of years the shrub have grown over the solar panels, and they are no longer working effectively.

For flat owners with solar thermal panels this can mean cold showers even in the height of summer, and for landlords or property management company's with a roof full of solar PV tied to land lords supply you can find that you ROI is reduced. The key is to pick the correct species for planting, and maintain regularly.

Species Mix for Bio-Diverse Living Roof

We "invented" the below mix as it suites most living roofs even when they have solar panels.

Living Roof Photo Gallery

The below photographs are taken at a site in London. This roof is described at a brown roof, but as you can see it is green in places, and also living in some areas too.

Green Roof with Solar Panels

Solar Thermal Panels and Shrubbery jostle for space on this living roof in Camden. This roof had a thick substrate, and so all manner of plants had established themselves. Some of which were overshadowing the solar panels, which is a bit counter productive.

Safe Working on Green Roof

Here you can see the small rail which is designed for use as an anchor whilst working at height. It is unclear how well plants have established them themselves in this are of the roof.

Green Roof Colonisation

Some larger flowers had established them selves, but where not wide spread. This living roof was in the order of 3 year old when we visited.

Removing a Green Roof

It was proposed to introduce a roof top terrace in this area, as you can imagine this was unpopular with planners. We wrote a specification that included for the introduction of a living wall, to offset area lost to trafficable surface.

Green Roof and Roof Top Infrastructure

A view showing other roof top infrastructure and how it fits with green / living roof planting. Satellite dishes, lift shaft head, light wells, and solar thermal panels can be seen.

Ladder

This roof is a multilevel living roof, and as such requires access ladders between levels for maintainance. The drainage channel you can see around the edge of the roof serves 2 purposes: 1 - to drain (!) and 2 - to stop plants growing in these areas, which is good. If you would like to talk about your living roof then please get in touch. Contact details are at the top of page.