[L+U NOTE: This is a guest post from Miles Chaffee from Milestone Imports]
“With the rising popularity of permeable pavement systems in residential and commercial landscape designs, it is important for landscape professionals to educate themselves about the different materials available for paving options. Natural stone is increasingly used as a permeable paver because of its durability and aesthetic appeal, as well as ability to facilitate water filtration and aid in land conservation. Stone such as Porphyry, a natural granite, is used today to design driveways, streets, walkways and parking lots.
While there are several materials that can be used for permeable paving, there has been a growing interest in natural stone as a resource for permeable paving systems because of the aesthetical appeal. The benefits of permeable paving include a more beautiful, user friendly environment that eliminates unsightly retention ponds and can reduce runoff by 80 percent or more. This eliminates puddling and flooding on parking lots while reducing snow plowing costs because of the rapid ice melt drainage.
The primary purpose in the design of a natural stone permeable paving system is to effectively reduce and manage the quantity of surface rain water 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 permeable paving allows the rainwater to filter back into the ground naturally.
By definition, for a surface to be permeable, it must allow for 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 allows 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 rain water runoff pollution. A full filtration system designed for permeable subsurface soils should allow the storm water 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 slowly release the water into a storm sewer.
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 and works to preserve woods and open space when using retention ponds. The customers can also benefit by using the additional space allowed in the building to increase the rental income of the building. This may also reduce overall development costs due to the reduction in storm sewers and other drainage methods otherwise required.
The different types of permeable paving have pros and cons. In terms of cost, gravel is the least expensive option. The drawbacks are that it requires frequent maintenance and renewal and the high upkeep increases the cost over time. Also, wheel ruts easily form in gravel which detracts from the appeal. Permeable concrete and asphalt are next in terms of expense, but studies have shown them to be prone to clogging, negating their efficacy. A study conducted be the Metropolitan Engineer’s Council in Denver showed a complete failure of permeable concrete under freeze-thaw conditions similar to those here in Santa Fe. The City of Rosemary Beach Florida tore out permeable concrete city streets due to clogging and replaced it with concrete pavers with permeable joints.
Brick, concrete, and natural stone pavers require that the material in the joints be permeable since the pavers themselves are not considered to be permeable. The brick must be the correct type and manufactured to specific requirements in order to be used as paving, especially in freeze-thaw climates. Constant freezing and thawing is harder on materials than climates that freeze and remain frozen for long periods. Concrete pavers offer a low cost option for paving and can last ten to fifteen years – just as brick can.
Natural stone is more durable – think of the Roman roads that were made out of Porphyry and other roads in Europe that were built centuries ago and still exist today. Again, the joint material must be permeable. Stone can be expensive but long outlasts other materials, which reduces the overall cost during the extend lifespan of the stone.
No matter the material chosen for a permeable paving project the benefits out weigh the additional costs. Permeable paving can free land designated for retaining ponds and has numerous environmental benefits. Done correctly with durable materials the paving can have a long life span and be aesthetically pleasing.
About the Author:
Founder and President of Milestone Imports
Miles has been active in the stone business for over 18 years. In 1996, he founded Milestone, Inc. which began as a small stone yard and tile store. As business grew and developed, Miles created a separate enterprise, Milestone Imports, in 2002 to focus on quarry-direct representation of Porphyry paving stones. Milestone Imports now represents Porphyry quarries from around the world importing and distributing throughout the United States, Canada, Japan, Taiwan and Hong Kong. Miles’ travels have carried him to diverse locations to promote Porphyry as a historically sound material that provides beauty and sustainable solutions to today’s modern challenges. He has traveled throughout the world to locate and research high quality materials with sound quarrying practices that lend themselves to the demands of his customers.