Brown Roofs

Industrial brownfield sites can be valuable ecosystems, supporting rare species of plants, animals and invertebrates. Increasingly in demand for redevelopment, these habitats are under threat. "Brown roofs", also known as "biodiverse roofs", can partly mitigate this loss of habitat by covering the flat roofs of new developments with a layer of locally sourced material.

Construction techniques for brown roofs are typically similar to those used to create flat green roofs, the main difference being the choice of growing medium (usually locally sourced rubble, gravel, spoil etc...) to meet a specific biodiversity objective. In Switzerland it is common to use alluvial gravels from the foundations; in London a mix of brick rubble and some concrete has been used. Although the original idea was to allow the roofs to self-colonise with plants, they are sometimes seeded to increase their biodiversity potential in the short term. The roofs are colonised by spiders and insects (many of which are becoming extremely rare in the UK as such sites are developed) and provide a feeding site for insectivorous birds.

Brown roofs for biodiversity

Similar to green substrate based roofs. In some cases it may be possible to use recycled aggregate from site and be generally left to colonise naturally or seeded with an annual wildflower mix or local seed source

Brown Roofs

The original concept of the brown biodiverse roof was to use recycled brick and
concrete form a local recycling plant. Although this was a good idea there are a
number of problems:

  1. the water holding capacity of the aggregate
  2. quality of the aggregate

Recent research and experience suggests the use of commercial crushed brick
or other porous type substrate to ensure quality and known water storage.
This type of roof will need higher organic content to ensure that the wildflower
plugs or seeds that need to be specified can flourish.

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