Permeable Pavers
Permeable Interlocking Concrete Pavers
Their Role In Green Construction
We all understand the value of permeable pavers in terms of their power to give us a hardscape surface that allows water to seap into the water table. The purpose of this article is to share specifc information about this material, which will allow the reader to understand the specifics of this product and to impact these details to your customers, particularly in reference to the role of permeable pavers in green design. Included is an outline of the main benefits of permeable pavers, which should allow you to have some basic information and facts at the ready. Please feel free to make a copy for yourself to use as a guide.
This overview looks at: some of the problems with hardscape surfaces the do not allow water to penetrate, Low Impact Design (or LID), and how it seeks to treat this problem, and some general information about how permeable pavers can accomplish this, in addition to stating how they conform to The Americans with Disabilites Standards, plus, some pointers on how these pavers can be used in LEED projects, and the areas in which they can be used for points.
Issues with Surfaces That Do Not Allow Water to Penetrate:
There are two main issues with these types of surfaces:
1. Overworked storm drains, causing excess, untreated water to run to rivers and lakes.
2. Pollutants flow directly to these water ways without undergoing treatment through natural biological processes.
Low Impact Development (LID): A design strategy with the goal of “maintaining and enhancing the pre-development hydrologic regime of urban and developing watersheds.” (Taken from the Low Impact Development Center website: www.lowimpactdevelopment.org) One of the goals of Low Impact Development is to reduce the percentage of impermeable surfaces in new construction.
Permeable Pavers Role in LID: Water passes through the upper lever of the pavers to a sub-level infiltration basin. At this level, water is filtered and undergoes natural biological re-processing, as opposed to moving directly to storm drains, and off to our oceans. Water is filtered slowly, and can be used on-site.
Infiltration: There is considerable debate on the infiltration rate of permeable pavers. The percentage of water that actually moves through the pavers must be figured considering the lifetime of the paver surface, and the type of soil beneath the surface. One study showed a mean infiltration rate of 3.5 inches of water per hour, for clean pavers (free of debris.) This study is here:
http://www.bae.ncsu.edu/stormwater/PublicationFiles/ICPIreport2004.pdf
Some producers of permeable pavers may suggest that the rate of water which passes through the pavers is much higher than this. Unreasonable claims of permeablity should be questioned.
Exfiltration: Rainfall may exceed the exceed the infiltration rate of the soil below. For different densities of soil, different exfiltration methods may be utilized in order to completely re-route water:
Full exfiltration: An installation situation in which the sub-soil is anticipated to exfiltrate all of the rain fall, without the assistance of additional drainage.
Partial exfiltration: For use when the soil may not exfiltrate all the surface water. In this case, a sub-surface perforated pipe is used to redirect the water.
No exfiltration: For use when the soil below has low or no permeability. In this case, an impermeable membrane is used at the bottom and sides of the system, in addition to a sub-surface perforated drain pipe.
Reduction of Pollutants: The aggregate filters and sub-grade soils the allow sedimentation to occur, and contribute through bacterial treatment of the pollutants and cation exchange. Growth of “good” bacteria has been found on established aggregate bases. In addition, because water immediately enters the permeable surface, it maintains a lower temperature, which means that unnaturally heated water does not enter the water habitats of wildlife, where it can cause shock or death.
Situations in Which Paver Should Be Avoided: Permeable pavers should be positioned at least 100 feet from wells, or natural water ways. Also, facilities or businesses that create by-products that are toxic should never use permeable pavers.
In addition, permeable pavers are highly subject to clogging when exposed to sediments or fines. The effectiveness of permeable pavers can be significantly reduced due to clogging. Pavers should be cleaned on a semi-regular basis in order to maintain maximum permeability.
ADA: Generally, to comply with ADA rules, the spacing of pavers should be a maximum of 1/2″.
LEED Credits:
Credit 6.1 and 6.2: Stormwater Design – 2 possible points (for achieving the appropriate percentage of permeable surface.)
Credit 7: Heat Island Effect Non-Roof – 1 possible point (for using light colored, high albedo materials)
MR Credit 4: Recycled content – 2 possible points (when using pavers that contain fly ash or blast furnace slag)
MR Credit 5: Regional materials – 2 possible points (when using materials that are extracted, processed, and manufactured regionally.
This article is intended as a general overview only. There are a myriad of other factors that we can explore in relation to permeable pavers, and we have included some useful links for those of you who wish to explore the subject in more detail. We always welcome your comments and feedback.
Mike –
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