Blue Roofs: - Urban Roof Ponds
Blue Roofs, a relatively new phenomenon, are a deviation from the more widely recognised Green Roof systems. They share similar characteristics with the Intensive Green Roof system, sharing a wide variety and range of plant and vegetation. However, their primary difference is in their deeper substrate base, which allows incorporation of a pond. This deeper substrate, approximately 300mm depth, contains more organic matter and retains more water, thus allowing establishment of a marshy habitat.
These roof systems are a natural and logical progression from Green Roofs, and are likewise to their Green counterparts, are suitable for a range of flat roof systems, bitumen felt, asphalt and single ply membranes. Although care should be undertaken prior to consideration to ensure the significant imposed loads of Blue Roofs can be supported adequately.
Unicorn Grocery - IKOgreen Roof System www.ecobuild.co.uk
Blue Roofs significantly improve thermal performance of a building, acting as a thermal store, (in the same fashion that the sea acts as a temperature moderator) reducing fluctuations in temperature and providing a cooling roof in summer, with additional warmth in winter; Particularly beneficial in mitigating Urban Heat Island effect, as witnessed in built up areas. The presence of a Blue Roof results in a ‘Warm Roof’ construction roof type, providing insulative materials above the existing roof decking, therefore avoiding the need for expensive Cellotex or similar insulation.
Incorporation of temporary water store results in a reduction in the rate of runoff and lag times from rainfall to entry into watercourses, whilst also acting to provide a natural water filter, absorbing pollutants. This reduces the burden on local drainage systems and water treatment plants, whilst reducing the threat of flash flooding occurring, as they may retain up to 75% rainwater, released back into the environment through condensation and transpiration.
An increase in plant and animal biodiversity can be anticipated, providing adequate design is carried out in the initial stages, as Blue Roofs cater for insects, amphibians and birds as well as a vast array of plant life.
This temporary storage of water can be used/ designed in conjunction with other water recycling measures, such as Grey Water recycling, use of Water Butts and or as part of a wider integrated energy management system.
Case study example:- Unicorn Grocery - IKOgreen Roof System. Unicorn Grocery in Manchester was treated to a biodiverse green roof which features a roof pond.
Blue roofs may be incorporated on existing or new build, and as part of an integrated design proposal, in conjunction with other environmental strategies, including solar panels, micro CHP to green walling. Other similar roof types include ‘Brown Roofs’ which are intended to encourage biodiversity, usually installed on Brownfield sites.
Sustainable Drainage Ponds
These may range anywhere from between 1m2 to 300m2, although generally cost in the region of £100m/2. Due to the relative nature of such ponds, the addition of fish is not recommended. Pond lining should be covered with substrate, added to encourage growth of pond vegetation. This should be inert, low nutrient material, to avoid excessive and overwhelming growth development. Hummocks and hollows should also be designed into pond margins. Include at the perimeter, a 2m buffer, with addition of piles of stones and or logs to provide hiding places for small animals. Avoid placement near large trees, which may overshadow the pond and new trees not planted immediately adjacent.
Attention should also be made to the presence of invasive plant species, which may mix, carried by birds or members of the public. It is recommended all plantations are native to the UK and that an ecologist is consulted prior to commencement of any Blue Roof construction.
Summary
As population pressures continue particularly in the UK, increasing swathes of green urban spaces are being swallowed up. Consequently, the value of such remaining spaces will increase, leading to many property owners, both residential and commercial to consider adapting their flat roofs for use as an outdoor space.
It is likely, in the increasingly environmentally conscious, consumer drive climate, Blue Roofs will become more common, not least to provide much needed outside space, but also for reasons of economic viability, improving property values, whilst reducing energy bills.