Consideration should be given to the sustainability credentials of the materials used between and around buildings, as well as to those used in the construction of those buildings. For precast concrete paving, the benefits are wide-ranging, says Colin Nessfield, secretary, Interpave.
The BRE Green Guide to Specification offers useful guidance on external hard surfaces as well as other important building elements. It rates various constructions from ‘A+’ for best environmental performance to ‘E’ for the worst, and it looks specifically at ‘landscaping’. Three different paving scenarios cover: pedestrian areas; lightly trafficked areas, such as car parking; and heavily trafficked areas. The same three scenarios with identical results are applied across the six different building types considered by the Guide.
The summary environmental ratings for a range of precast concrete paving specifications covering blocks, flags and ‘grass concrete’ units are generally ‘A’ or ‘A+’ across all three scenarios. The latest edition of the Guide also specifically confirms that SUDS (sustainable drainage) techniques, such as concrete block permeable paving, can be considered to have the same ratings as their conventional equivalents. This is because “the additional material that may be necessary for SUDS is discounted, as the benefit it provides is for facilitating drainage and therefore sits outside the scope of the functional unit.”
These Guide ratings provide independent endorsement of the low environmental impact of precast concrete paving, particularly in comparison with imported materials, and reflect the ongoing environmental investments and improvements made by Interpave manufacturer members, as well as by the cement industry generally. Although not considered in the Guide, precast concrete kerbs will have similar environmental characteristics to concrete flags, whereas alternative kerbing materials such as plastic remain an unknown quantity.
Localised material sourcing and product supply are also important for precast concrete, and equivalent paving products shipped into the country bear a substantial CO2 emission load. In fact, some imported stone paving products are included in the Guide generally with much poorer environmental ratings than their precast concrete equivalents and half with the worst ‘E’ rating. Green Guide ratings also form an important part of BREEAM assessments. For example, with the Educational Building version, one credit is 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.
Unfortunately, the Code for Sustainable Homes (CSH) does not cover paving materials. However, it does follow BREEAM in acknowledging the importance of SUDS to meeting a range of different requirements. Undoubtedly, one of the most important environmental benefits of precast concrete hard landscaping is concrete block permeable paving (CBPP) used as part of SUDS. It reduces the amount and rate of runoff, and removes many of the pollutants in that runoff.
Importantly, CSH Category 4 surface water runoff looks for housing developments which “avoid, reduce and delay the discharge of rainfall to public sewers and watercourses. This will protect watercourses and reduce the risk of localised flooding, pollution and other environmental damage”. One of the mandatory elements aims to ensure that the peak rate of runoff into watercourses is no greater for the development than it was for the pre-development site. In addition, two credits are available for using SUDS to improve water quality of the rainwater discharged or for protecting the quality of the receiving waters.
Events have now overtaken CSH in this area as the Flood and Water Management Act 2010 takes effect in England and Wales. It applies to any construction work that creates a building or other structure, including “anything that covers land (such as a patio or other surface)” that will affect the ability of the land to absorb rainwater. In other words, all new buildings, roads and other paving, whatever the size, type or scale of the project, will be affected as well as alterations that have drainage implications. The act may well apply to work that does not need planning permission, although applications for approval can be made with planning applications.
When the act takes effect, construction works cannot start until drainage systems have been approved by new ‘approving bodies’ generally county councils or unitary authorities in line with new national standards for SUDS. The existing right to connect surface water drainage systems to public sewers will be restricted to those approved under the new regime, ie appropriate sustainable drainage. Approving bodies will be obliged to adopt all approved drainage systems except those on single properties and public highways. Road drainage will still be adopted by highways authorities, although design, construction and maintenance must also be in line with the new national standards.
It is expected that these national standards will be published shortly and will cover the basic design, construction, maintenance and operation of SUDS. In the case of CBPP, detailed guidance has already been developed by Interpave on all of these, and other issues, based on extensive international experience. This should form the basis of national standards and also provide more detailed, specific guidance. It will help satisfy the expected growth in the use of concrete block permeable paving, which meets a range of needs that other SUDS techniques cannot. For example, it can handle runoff from roof drainage, as well as adjacent impermeable surfaces, and requires no additional land-take, unlike ‘soft’ landscaping features such as swales or ponds, making it efficient for high-density projects. It also satisfies the new act’s specific definition of SUDS both to reduce flooding and to improve water quality, unlike attenuation tanks, which only address the former.
Both CSH and BREEAM consider other issues where CBPP can play a useful role as well for example, with the recycling of rainwater and reduction in the amount of mains potable water used for external uses like irrigation and car-washing. There is also potential for use of this stored water for WCs and washing machines instead of potable water, and CSH offers up to five credits for savings here. And the beneficial impacts that CBPP can have on wildlife for example, by avoiding gulleys which can trap animals can contribute to credits available for ecological value.
Precast concrete paving is at the heart of PRP Landscape Architects’ winning design for the sustainable landscape project at the BRE Innovation Park near Watford (pictured right). Three Interpave members donated products to the project, intended to bring together the very different individual houses on the Innovation Park as a sustainable community. A limited palette of subtle colours helps to unite the diversity of architectural styles and to develop a sense of place with coordinated themes.
Although designed effectively as a Home Zone, the new paved area also has to accommodate some very non-domestic traffic including 23m-long vehicles as it remains a central artery of the BRE research site. Precast concrete permeable paving is used throughout the new Home Zone and is already installed in other, earlier areas of the Innovation Park. Of particular interest, an innovative geothermal paving system which captures enough heat from within a 50m2 area of concrete block permeable paving to heat a house is being monitored by BRE