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Pave Your Way to a Green Future
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As the sustainability and economic impact of residential and commercial developments become increasingly important in our society, homeowners, developers and government officials look to landscape architects who can offer environmentally-friendly solutions that are both cost-effective and aesthetically pleasing. In an industry that is consistently developing innovative ways to be more efficient and environmentally responsible, landscape architects are looking to a method that has been used since the Roman Empire. Permeable paving methods have been used for thousands of years, but only recently have landscape architects started to use this method to market themselves as eco-savvy.
As the green movement intensifies, it is important for landscape professionals to educate themselves about the different materials and methods used for permeable paving. The Romans used Porphyry, a natural granite stone, to pave their streets and walkways. The Porphyry pavers were set using a porous material in the joints to allow water to filter back into the ground. This early method remains a viable option today and isincreasingly used by landscape architects and designers who are learning from the past to design the future.
What is permeable paving and what are the benefits?
For a surface to be considered permeable, it must allow water to penetrate the surface through porous openings. In segmental or unit paving, like natural stone or brick pavers, the joints are what make the surface permeable. Some surface materials, such as gravel, do not have a solid surface and therefore allow water to pass through to the subsurface.
Typically a subsurface for segmental permeable paving would be designed using a crushed stone base which would provide filtration and partial treatment for rainwater runoff pollution. A full filtration system designed for permeable subsurface soils should allow the stormwater to penetrate the surface and filter through the base course and the native soils back into the aquifers. If the capacity of the soil to filtrate the water is exceeded, the base may be designed to filter, partially treat and then slowly release the water into a storm sewer.
While there are many environmental benefits of permeable paving, the primary purpose in the design of a natural stone permeable paving system is to effectively reduce and manage the quantity of surface rainwater runoff while accommodating pedestrians, vehicular parking and traffic. Permeable paving has proven particularly valuable in existing urban developments where the need to expand parking areas is hindered by the lack of space due to retention ponds. In these situations, permeable paving is a cost effective way to create parking areas, while eliminating the need for some retaining ponds, since the permeable pavers allow rainwater to filter back into the ground naturally. Other benefits of permeable paving include a more beautiful, user friendly environment that eliminates unsightly retention ponds and reduces runoff
by 80% or more. This eliminates puddling and flooding on parking lots. Additionally, the improved drainage speeds up the ice melt process, which reduces snow plowing costs.
For the landscape professional and the customer, it is important to note that this system also promotes tree survival by providing air and water to the roots. Using a subsurface water retention system also helps to preserve wooded areas and open
landscapes by eliminating the need for surface ponding. Developers may also gain . This may also reduce overall development costs due to the reduction in storm sewers and other drainage methods otherwise required.
What permeable paving options are available?
Each type of permeable paving material has its advantages and disadvantages. In terms of cost, gravel is the least expensive. However, it requires frequent maintenance and renewal, which over time, adds up to a higher cost for materials and labor. Permeable concrete and asphalt are next in terms of expense, and studies have shown that these materials are prone to clogging, negating their effectiveness. A study conducted by the Metropolitan Engineer’s Council in Denver, CO, showed a complete
failure of permeable concrete under freeze-thaw conditions. Due to pervious pavement issues with clogging and vulnerability to freezethaw, the material is not ideal for all situations or climates. In fact, some
cities have removed pervious asphalt and concrete pavement because of the problems with clogging and continued maintenance.
Another option for permeable paving is brick, concrete or stone pavers with permeable joints. The permeability and water-flow-through rate is dependent on the porosity of the material in the joints, the size of the joints and the entire substrate design. The joint material should adequately allow the passage of water to quickly drain, possess structural capability to withstand traffic loads and provide horizontal stability to the paving surface. Permeable pavers have the ability to infiltrate rapidly compared to most soils and a conservative approach should be taken in designing the system.
Natural stone materials, such as Porphyry, have been used for centuries throughout the world and have proven to be an excellent choice offering beauty, longevity and low maintenance. Natural stone life cycles are measured in decades with studies showing typical minimum of 60 years. Granites such as Porphyry last for centuries. Porphyry is extremely dense with a porosity of less than .6%. Using it in a permeable setting system requires the same pervious materials for the joints and attention to the details of the substrate discussed earlier, but offers an unparalleled surface for durability, low maintenance and overall functionality. The natural surface also meets the American Disability Act (ADA) for slip resistance and smoothness and is inert to chemicals.
In Summary
It is beneficial for all landscape contractors to educate themselveson the art of permeable paving. With the rising popularity of segmental pavers, such as Porphyry, and the ecological benefits of permeable paving, it is likely that the demand for segmental permeable paving will
continue to increase in the future. Cities such as Chicago, Boston and Detroit have started initiatives to “Green” their cities by installing permeable paving for storm water management. Other cities have allowed property owners to use more of the land area
by shrinking or eliminating retention ponds if permeable paving is used on the property. It is necessary for a landscape contractor to have an understanding about the different types of permeable paving options available to fit their customers’ specific projects and capitalize on the growing number of Green initiatives in their
markets. No matter the decision on the materials, it is essential for landscape architects and designers to fully understand the intricacies of permeable paving and different options available.
About the Author
Miles Chaffee is the founder and president of Milestone Imports, the largest importer of Mexico Porphyry in the U.S. with exclusive rights to the largest porphyry quarry in Mexico. Chaffee has developed a course called "Porphyry as a Permeable Pavement" offering free educational learning
credits to more than 12 organizations in Canada and the US. and travels extensively presenting seminars on different and historical methods of setting Porphyry pavers. For more information about Milestone Imports including a free Installation Manual and project photos CD, visit www.milestoneimports.com, contact
info@milestoneimports.com or call (866) 641-1999. |
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