Greening

The use of green walls and roofs can, among other things help to minimise the impact of rising temperatures in the city (what is often know as the 'heat island effect'), contribute towards better air quality, reduce surface water run-off and contribute to local biodiversity and well being.

Green walls

These normally incorporate permanent trellis work, spaced off the masonry, to support non-clinging climbers. They can be designed to avoid structures, gutters and downpipes, confining climbing vegetation to the wall itself.

Climbing plants should be planted at least 40cm away from the wall in an irrigated plant pit stocked with nutrient-rich topsoil. Green walls have also been combined with trickle irrigation systems and growing media to support non-climbing plants directly on the walls themselves.

Green walls protect masonry from extreme temperatures, air pollution and rainfall. They can also provide nesting and feeding habitat for birds (particularly Wren, Robin and Blackbird), honeybees and other insects. Native plant species suited to creating climbing green walls include Honeysuckle (Lonicera periclymenum), Hop (Humulus lupulus) and Traveller’s Joy (Clematis vitalba). In urban areas, exotic climbing species can also provide nature conservation benefits.

Green roofs

Green roofs are constructed from layers of impermeable membrane, cushioning and a growth medium to provide a habitat for vegetation. Intensive living roofs, with soil depths of over 350mm can support trees, shrubs and even water features. Intensive roofs add a significant additional load to the roof structure and usually require substantial maintenance.

Extensive living roofs have substrate depths of between 25mm and 125mm. They can support a range of plants and growing mediums and add much lower loading to the roof structure than intensive roofs. Extensive roofs can be planted with Sedum spp. (either plug planted or as preplanted mats) or a range of native grassland plants, using locally sourced growing mediums (‘biodiverse roofs’). Biodiverse roofs tend to be more attractive to wildlife. Biodiverse roofs are self-sustaining, although they often benefit from an autumn clean-up.

In addition to ecological and aesthetic improvements, green roofs can provide a range of other benefits. 

• a typical green roof can hold 55% of its volume in water, they can slow storm runoff and reduce flood risks;
• help to cool urban areas in summer and promote energy efficiency.
• attract media interest and create a positive company image;
• lower maintenance costs than conventional flat roofs because the roof itself is protected from UV radiation, frost and other mechanical damage.

Some of the green roofs available include:

Chalk grassland

This is arguably the most appropriate type of green roof to use in Brighton & Hove given that it uses locally native vegetation and local growing media.

Chalk grassland plant community on the roofs in the city were found to have provided compensatory feeding habitat for House Sparrow, Pipistrelle Bat, Song Thrush and other wildlife, contributing to meeting targets set in the Local Biodiversity Action Plan.

Sedum

These are perhaps the best known treatment for green roofs, being used widely in the UK. Sedum plants are small, succulent, drought resistant, ground cover plants that protect the roof membrane and spread across roofs easily.

Plants are often supplied as mats to be rolled onto a roof surface after waterproofing and draining layers have been supplied. A drainage mat is needed on flat roofs with less than 3 degrees of slope, to make sure the plants for living roofing systems never get waterlogged. A handy upside of this is that unwanted weeds will not be able survive on the small amounts of water that sedum roof plants thrive on.

Shingle (brown roof)

Brown roofs usually utilise local soil and spoil to provide the substrate for the roof, the roof will often initially be brown in colour. However, over time plant species will grow over this substrate and the end result will tend to be a green-coloured roof.

They are flexible in design and can be tailored to meet the requirements and specific sustainability targets. They could utilise recycled material and spoil from a local building site to attract wildlife.

Relevant policies

Brighton & Hove Local Plan
SU2: Efficiency of development in the use of energy, water and materials
QD17: Protection and integration of nature conservation features
QD18: Species protection
QD19: Greenways
NC2: Sites of national importance for nature conservation
NC3: Local Nature Reserves (LNRs)
NC4: Sites of Nature Conservation Importance (SNCIs) and Regionally Important Geological Sites (RIGS)

Local Development Framework
SPD08: Sustainable Building Design
SPD 11: Nature conservation in development