Code Level 6 Barratt Green House (shown here) and
the adjacent Level 4 Hanson EcoHouse at the BRE
Innovation Park use concrete block permeable paving
for rainwater harvesting.
There are a number of – perhaps surprising – environmental implications of using precast concrete paving. Precast concrete paving products are inherently thin with a large relative surface area enabling them to re-absorb significant amounts of CO₂ from the atmosphere during their lifetime.
In our towns and cities, using materials with a high albedo, such as concrete block or flag paving, in place of asphalt can reduce the impact of development and reduce the urban heat island effect. Urban heat island occurs where an urbanised area is significantly warmer than its rural surroundings. Precast concrete paving also differs substantially from asphalt in terms of luminance, or the amount of light reflected off the paving. For asphalt, luminance is only about 7% whereas block paving achieves between 15% and 30%. This often-overlooked area has implications for street lighting design and safety in terms of contrasting pedestrians against paving at night.
Undoubtedly, one of the most important environmental benefits is concrete block permeable paving as part of sustainable drainage systems (SUDS) which form part of government planning policy around the UK. Unlike conventional paving which requires runoff collection by gulleys and pipes, concrete block permeable paving acts as the drainage system as well as supporting traffic loads. It allows water to pass through the surface - between each block - and into the underlying permeable sub-base, designed specifically for this role. Here, it is stored and released slowly, either into the ground, to the next SUDS management stage or to a drainage system, or alternatively harvested.
BREEAM (Building Research Establishment’s Environmental Assessment Method) and the Code for Sustainable Homes (which will, inevitably, play a major role in the eco-towns currently proposed by government) address the benefits of concrete block permeable paving as a sustainable drainage systems (SUDS) technique. Concrete block permeable paving reduces the amount and rate of runoff, and removes many of the pollutants in that runoff. It can also benefit biodiversity by providing unpolluted water for wildlife, plants and trees, while eliminating the hazards that open gulleys present to wildlife.
Many of these benefits are recognized with credits in BREEAM 2008. For example, one credit is offered where SUDS are used to limit runoff from a development to that of the site’s natural state and another where SUDS provide on-site treatment to minimize watercourse pollution. Credits for beneficial impacts on local ecology are also available, where permeable paving can contribute. Using permeable paving to harvest water for irrigation is also recognized with a credit, as is harvesting for toilet and urinal flushing. Some similar provisions are included in the Code for Sustainable Homes.
In addition, BREEAM specifically recognizes the best ratings from the BRE Green Guide with 1 credit available where at least 80% of the combined area of external hard landscaping and boundary protection specifications achieve a Green Guide A or A+ rating – generally the case with precast concrete paving.
