building fabric
The sustainable contribution of green and brown roofs
The large numbers of roofs in education requiring an upgrade present an opportunity to transform the sector’s carbon footprint, says DAVE COOK.
coverings, especially in education where the Government has specific targets aimed at reducing carbon emissions. Today, there is a growing range of options in green and brown (or ‘living’) roofs. A green roof consists of a living, vegetative system made up of a growing medium and vegetation layer at its outermost surface. The design and construction between the roof deck and the growing media varies, but usually incorporates a geo-textile filter, drainage layer, root barrier and a waterproof membrane. The growing media depth can vary from 20mm for sedum-type plants, up to one metre if large shrubs are chosen as part of the vegetative system. An advantage of placing the insulation above the waterproof layer and below the substrate and ‘living element’, which is possible on a green roof, is that it is
S
Some schools incorporate solar PV with Green or Brown roofs to improve sustainability even further
USTAINABILITY is an important consideration when it comes to selecting materials for roof
protected from temperature extremes, and that can mean an enhanced lifespan for the whole structure.
A question of control A brown roof is similar to green roofs in that they are both constructed in the same way. However, with a green roof, the plants are introduced from the outset, and therefore the biodiversity is controlled, to some extent. With a brown, the overriding aim is to encourage biodiversity. That usually involves utilising local soil and spoil to provide the substrate, which means that the roof will often initially be brown in colour. However, over time plant species will colonise this substrate and the end result will be a roof that nature has had a large hand in creating. Brown roofs, unlike green roofs, have
less of a ‘landscaped’ element to them and are intended to evolve naturally into their own ecosystem. The appearance will
change as the natural ecosystem grows and matures with wild flowers, herbs and rare plants that are native to the surrounding area. The suitability of green and brown
roofs depends on a number of factors, including budget, planning and time constraints. Green roofs are more appropriate for schools or colleges looking for an instant green finish, whereas it can take around three years for a brown roof to establish itself. Dave Cook is regional contracts director at Bracknell Roofing.
www.bracknellroofing.com
Benefits
• Reduced energy use: Living roofs absorb heat from the sun and act as an insulator for the building
• Visual appeal, especially for schools in built up, urban environments
• Improved air quality: Vegetation growing on living roofs can remove air pollutants, whilst absorbing carbon dioxide
•Green roofs can reduce the urban heat island effect
•Living roofs reduce the impact of flash storms and meet the requirements of SUDS
•They are able to provide noise insulation for schools under flight paths and around airports.
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educationdab.co.uk
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