Masonry Magazine April 1995 Page. 18
Sustainable Development
Sustainable development can be defined as development that meets the needs of the present without compromising the future. In the past, sites were often dramatically altered without adequate consideration of the environmental impact. As with all designs, compromises must be made to achieve the design requirements. Sustainable development takes into account the effects of materials used in the landscaping plan on the environment. The embodied energy and the effects of the manufacturing of the material on the environment are closely considered. Brick is a material made from clay and shale, some of the earth's most abundant materials. The energy used to make brick, which is termed its embodied energy, is less than that of concrete, steel and many other materials [3]. Since brick is inert, it does not pose any long-term environmental threats.
Water Issues
Environmental concerns have been raised regarding both storm water runoff and the lack of water in some areas. When many parts of the landscape are being covered by impermeable surfaces, storm water runoff becomes a larger problem. The amount of water that drains off of a shopping center parking lot, for example, can be quite large causing flooding or erosion. Thus, the size of storm sewers and catch basins must be increased in size accordingly, putting more stress on the infrastructure. Conversely, some areas of the country are so arid, they cannot support plant life.
Porous Pavements
Most hardscaping materials, such as concrete or asphalt, will not allow water back into the ground. This is also true of rigid (mortared) brick pavements and some flexible (mortarless) brick pavements over an impermeable base. These systems can have a negative effect in urban areas which include trees as a part of the urban landscape. Trees can die due to lack of water and nutrients when surrounded by impervious hardscapes. In an effort to provide water for trees, grates have been used, but their small size can inhibit proper tree growth. Soil and mulch have also been used around trees, but usually become compacted and allow rain to evaporate away too quickly. When water infiltration into the ground is desired, a pavement which allows water to percolate back into the ground should be used [4]. One alternative that can help water infiltration and reduce storm water runoff is the use of porous pavements.
A porous pavement allows water to filter through it, percolate back into the ground and replenish the ground water. In most cases, mortarless brick paving over an aggregate base can be constructed to allow water to percolate into the ground. However, to allow more percolation to occur, the pavement must have joints between the pavers at least 4 in. (6 mm) wide. The joints allow water to enter easily and permeate to the base. The base should be an open-graded aggregate, such as free-draining gravel or sand, to allow percolation. Although porous pavements allow storm water runoff to be directed back into the ground water system, it may go against usual pavement design practice. In a flexible brick pavement, it is desirable to have a dense base to resist loads from traffic above and from frost heave from below. Using an open-graded base may not provide the stable base that is needed.
To use an open-graded base under brick paving, some simple recommendations must be followed. The open-graded base must be compacted appropriately. Guidelines exist for the proper construction of open-graded bases [6]. A membrane, such as a geotextile or filter fabric membrane, must be placed between the sand setting bed and the open-graded base to avoid settling of the sand into the voids of the base. A geotextile may also be required between the base and the soil or subgrade to prevent soil from pumping up into the base. The size of the joints can be problematic when large amounts of water constantly run across the pavement. Jointing sand may wash out in areas when the joints are larger than in. (6 mm). Another issue to consider is that interlock of the pavers will not be achieved when the joints are larger than % in. (6 mm). Interlock of the pavement occurs when the pavers are compacted into the sand setting bed and the entire pavement i.e. pavers, setting bed, and base lock together and act to withstand the loads as a single element. A flexible brick paving system can be designed for improved percolation, but interlock of the pavement cannot be expected when sand-filled joints are larger than in. (6 mm).
Xeriscapes
Xeriscapes are defined as water-efficient landscapes which not only require less water to grow vegetation, but have a reduced need for mowing, fertilizing and pesticide application. They may be used in certain areas of the country, such as parts of Southern California, Arizona and Nevada, where water supplies are low or unreliable. Instead of introducing planting areas that require large amounts of water, it may be prudent to use brick in the place of plants. In this manner, reliance on the local water system, expensive watering systems and plant maintenance can be reduced. Wildfires in arid regions of the country are another concern which may require the use of non-combustible materials adjacent to homes. Brush and shrubs can act as fuel sources for wildfires. Brick paving adjacent to the house can act as a fire break. To offset the use of all of the hardscape materials, patterns are laid in the pavement to give the impression of plantings. Obviously, this must fit in with the entire landscaping plan.
Aesthetics
One of the most important features that a landscape architect faces is that of appearance. The look of any design can evoke strong feelings, good or bad. So it is important that the aesthetics of the project be examined closely. As in all architecture, form, color and pattern are the vehicles for achieving a certain aesthetic appeal.