By Anne Cosgrove
Published in the June 2008 issue of Today’s Facility Manager
Mostfacilities have paved areas on their property, whether in the form of aparking lot, sidewalk, plaza, or all of these. And, all facilities mustdeal with stormwater management. The rainwater not absorbed by soil ona site must travel somewhere, and, in most cases, this overflow goesinto sewer systems or directly into natural water sources, such as anearby stream or lake.
Stormwater management demands that the facility manager (fm) payattention to where the rainwater is going. An immediate concern isflooding, so fms work to ensure that the infrastructure is in place ontheir properties to handle this. But besides this issue, stormwatermanagement brings environmental and financial issues to the forefront.From an environmental standpoint, there is concern about chemicals anddebris being “picked up” by stormwater and ending up in natural watersources. Financially, as public infrastructure in many locations iscoming due for upgrades, municipalities and other water managemententities have begun to increase the fees associated with handlingstormwater runoff from properties.
If an fm is facing challenges with the environmental and/orfinancial issues related to stormwater, porous paving may offer asolution. Also referred to as “permeable” or “pervious,” this type ofpaving enables rain to flow through openings in its construction. Thesoil below then has the ability to absorb the water, returning it tothe ground.Depending on the rainfall that occurs at a location, this mechanism caneliminate stormwater runoff. However, in most cases, the soil does notabsorb all of the rain, and the facility will still need to maintain astormwater management system.
While many paving surfaces could be considered porous, InvisibleStructures, a porous paving provider located in Golden, CO, definesthis type of paving as “that specifically designed and constructed toencourage rapid infiltration and percolation of rainfall and stormwaterthrough the entire pavement cross section.”
The U.S. Green Building Council (USGBC) includes stormwatermanagement credits in its LEED rating systems, and “permeablealternatives” to leaving a site untouched are suggested as ways toreduce the impervious spaces on a site.
Explaining the motivation for offering credits for stormwatermanagement (of all kinds), Corey Enck, manager, LEED certification atthe USGBC, says, “The main reason is to limit the disruption of thenatural stormwater flows. Typically, where there are pervious areas,stormwater is absorbed into the earth and used by the vegetation. Italso recharges the underground aquifers. With impervious paving, thatdoesn’t happen, and it creates runoff, which can lead to negativeeffects of excessive stormwater runoff. That is what the LEED ratingsystem is trying to address.”
Not all areas of a facility site may be appropriate for porouspavement. Each project must be considered in terms of its specificrequirements. But, in many scenarios, such an installation can benefita facility. There are appropriate applications for each, and thedesigner must determine which is best suited to each project, orportion of a project.
In his LEED certification activities, Enck says he sees many morenew construction projects specifying porous paving options compared toexisting buildings. “Typically with an EB [existing buildings] project,there would be more cost to tearing up their hardscape and replacingit,” he says. “We see it more often in a new construction project whereinstead of paving a parking lot, they would go with pervious paving.”
In terms of where on a project site porous paving is more likely tobe used, Enck continues, “We see it everywhere on a site. However, itis more common for use on smaller areas, such as pedestrian ways. Orinstead of doing their entire parking lot with impervious pavement,some projects will do a portion with pervious and a portion that’snot.”
Porous pavements are generally appropriate for applications wheretraffic moves slowly (less than 30 mph) and/or infrequently, such aswith fire lanes, service drives, overflow or all day parking, andpedestrian areas. Enck notes the majority of projects he inspects forLEED certification (that are pursuing credits for stormwatermanagement) do not use porous paving in that pursuit. However, heestimates that about 20% do, and those “that are going the perviouspaving route are typically installing open cell paving systems-aconcrete grid with vegetation in between.”
Porous paving is competitive with asphalt paving and has a lowerlife cycle cost due to reduced maintenance costs and surfacereplacement needs. According to literature from Invisible Structures,asphalt paving requires resealing every two to four years, whileresurfacing requires this maintenance every eight to 15 years,depending upon traffic weight, traffic volume, and climate.
Maintenance costs for porous pavements over a 12 to 15 year period(asphalt life cycle) will generally cost between 60% to 90% of asphaltmaintenance/repair costs, states literature from Invisible Structures.And, the company notes that a properly installed pavement can beexpected to perform over a life cycle of 50 to 100 years. The upheavalto an existing facility, along with the initial costs, can deter fmsfrom pursuing this course for their sites already in operation.However, with environmental concerns growing and stormwater relatedfees rising in many areas, this type of installation may become anincreasingly attractive option.
Research for this article included information from Enck, along with literature from Invisible Structures, Inc.
Have you installed porous paving at your facility? Share your experiencing by sending an e-mail to [email protected].