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Permeable Pavement Options for LEED Projects

by Chad Ludeman on December 8, 2010 · 16 comments

in landscaping,LEED,materials

We have started to explore larger projects with our development company in Philadelphia that include shared off-street parking lots with a common driveway. This provides a new opportunity to explore more sustainable pavement options than the traditional blacktop used in most projects. Part of our research, as always, is devoted to finding the best mix of sustainability and cost so that we, and others like us, can actually have a chance of implementing something new on a for-profit project.

First, a bit of quick background on how Philadelaphia’s Water Department is actually encouraging projects to use permeable pavement in larger projects. In Philly, the city requires projects that exceed 15,000 square feet of area to develop an approved Stormwater Management Plan. Typically this involves large underground detention basins and extensive piping. There is also a lengthy design process typically associated with the Philadelphia Water Department.

Fortunately, the PWD provides incentives to builders to fast track their design and approval process for stormwater management if they can satisfy the needs via “green” methods. This typically always includes some type of pervious paving surface where impermeable would typically be installed and a method of delaying roof runoff from entering the city sewers (think green roofs or giant rain barrels).  Yea Philly!

OK, now on to the different options available in pervious surfaces that you can drive a car or even a large truck over. We’ll cover the main types that we have run across and you can tell us what we’ve missed in the comments. All of these systems are installed in a similar fashion. There is often a bit more excavation and up to a foot of crushed stone or gravel installed prior to the paving surface in order to help facilitate collection and storage of large rainfalls without the surface experiencing flooding. Simple, smart and effective. Read on and enjoy my rating system.

Porous Asphalt (Blacktop)

That's a fancy stream of water!

Porous Asphalt, or Blacktop as the kids say, is one of the more popular options out there as it seems to be the most cost effective and widely accepted. After all, it looks pretty much like normal blacktop and asphalt is king for most of our roads and parking lots.

Cost – $
Maintenance – Lots
Porosity – ~176″/hour
Ability to Grow “Green Things” – 0 out of 5
Overall Sustainaearthgreenfriendliness – D+

The Asphalt starts out strong with low cost and effective porosity, but quickly loses points for requiring a lot of maintenance, zero ability to grow anything, being nasty and a strong contributor to the urban heat island effect. Don’t get us wrong, it’s much better than standard asphalt. We’d just prefer one of the other alternatives a bit more for smaller projects that don’t include thousands of miles of roadways.

The maintenance we are talking about is a biannual cleaning with a giant commercial vacuum type device to keep the voids in the blacktop from getting clogged over time. Sweeping or pressure washing won’t do and may only contribute further to premature clogging. Check out the National Asphalt Pavement Association for more info.

Pervious Concrete

Oooooooooh!

Pervious Concrete is the same concept as porous asphalt, except it’s concrete. It’s very easy to order and have installed by a skilled flatwork contractor, even if they have never used it before as it is basically normal concrete with no “fines” in it. This is how it remains open to water infiltration. A benefit over asphalt is that is will result in a much lighter color that will not contribute to the urban heat island effect as much. It is still concrete though and comes with the carbon footprint associated with concrete if you’re counting carbon points on your project. A bit costlier to have installed than porous asphalt, it is a choice we prefer if options are limited.

Cost – $$
Maintenance – Lots
Porosity – ~480″/hour
Ability to Grow “Green Things” – 0 out of 5
Overall Sustainaearthgreenfriendliness – C

One way to reduce your carbon footprint with any concrete order is to insist on local or even reclaimed aggregates and push for the highest amount of Fly Ash and/or Slag which are both reclaimed waste products. Pervious Concrete also requires the same biannual sucking that porous asphalt recommends. Check out PerviousPavement.org for more info on Pervious Concrete.

Pervious Block Pavers

Most commonly seen permeable concrete paver

There are many different types of Pervious Block Pavers popping up on the market now that the concept of saving the earth is gaining popularity again. The most commonly seen permeable paver is shown to the left and creates a hexagonal shape of concrete around a central pocket where grasses can be planted or simple gravel can be filled in.

Cost – $$$
Maintenance – Some
Porosity – Varies
Ability to Grow “Green Things” – 3 out of 5
Overall Sustainaearthgreenfriendliness – B+

That tire is really working up a sweat.

Since the popularity of this interlocking concrete paver had increase, more varieties have hit the market that look more like traditional pavers. An example is shown to the right. These pavers have less open area that is usually created either at the corners or by spacing the pavers on all sides to allow for infiltration. This type of paver can not grow anything in the voids, but is typically filled with gravel. It’s a nice option for those that want the traditional paver look with boosted functionality.

Tbe biggest deterrent to these types of pavers is the cost. Not only are the pavers themselves pricey, but the cost of install is typically much higher than the other varieties of permeable paving due to having to lay individual, small blocks by hand. There can be some maintenance with these pavers as they may individually settle or become misplaced after some use. They may also be damaged easier than a uniform pavement by snow removal in the winter. There are too many suppliers of these products for me to point to one source, but Google can help you out if interested in more info.

Drivable Grass

Drivable Grass with grass, sand, gravel & mulch filler

Drivable Grass is a specific product manufactured by the Soil Retention company. It’s kind of a unique product that we recently stumbled across at Greenbuild that I felt deserved it’s own category. The product melds a bit of the benefits of the other products into one system.

For starters, is comes in 2′ x 2′ mats that are much more affordable to have installed than the individual pavers. It also has a much larger exposed area (61%) for greater infiltration and more room to grow grass or ground cover in if desired. Also, unlike the traditional hexagon turf pavers, this system does not isolate the plant material into individual pockets. This allows the plantings to remain cooler and receive more uniform watering. These benefits result in a greener parking surface than most of the alternative plantable systems.

Cost – $$
Maintenance – Very Little
Porosity – I couldn’t find a spec. Sorry.
Ability to Grow “Green Things” – 4 out of 5
Overall Sustainaearthgreenfriendliness – A

Currently, this is our top choice to use in a few of the sites we are looking to develop in Philly that have shared parking areas. It looks like the cost will be less than permeable concrete and we will get the added benefit of creating a green space in the parking lot that requires much less maintenance than other systems which will reduce the HOA fees for the home owners. All good things so far.

Plastic Grid Systems

Yes, you can drive on these plastic cup things

Cost – $$
Maintenance – Very Little
Porosity – Lots
Ability to Grow “Green Things” – 5 out of 5
Overall Sustainaearthgreenfriendliness – A

Last but not least are the plastic grid varieties of permeable paving systems. Some of these get extra points for being made of recycled plastic and being fully recyclable themselves. We have done the least research on these systems, but the install seems straightforward and it can result in a fully sodded surface if desired. The main issue we saw was that it is recommended for light or occasional use parking lots if you want to maintain the grass on the site. If anyone has any experience with this type of product, please speak up in the comments.

Conclusion. That’s all I have. Contribute below.

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Permeable Pavement Options for Green Projects | Birmingham, AL - Home Builder, Construction, and Remodeling - Shield Properties, Inc.
December 8, 2010 at 10:28 pm

{ 15 comments… read them below or add one }

1 DavidPopoffCt December 8, 2010 at 5:02 pm

I really like the idea about Pemeable pavement but how do you control frost heaves here in the northeast and does the snow plowing rip up the surface like gravel.

Thank you.

2 Terrell Wong December 8, 2010 at 6:29 pm

try Modi pavers – they are like lego for driveways. easy to install – modular and therfore easy to change or fix. similar to the one above but also allows for gravel finish for those who do not wish to mow their lawn

Terrell

3 David Liguori December 9, 2010 at 3:43 am

Chad,

You neglected to mention one of the most important “green” benefits of pervious concrete. It has been well established that the open matrix of both the pavement and base layer act as a very effective bio-filtration system, cleaning up much of the pollutants that would otherwise go into our waterways. Here is an example of what the research is showing:

Pollutant Removal (%)
Study TSS TP TN COD Metals
Prince William, VA 82 65 80 - -
Rockville, MD 95 65 85 82 98-99

In addition;
-pervious concrete uses approx. 25% less cement (the source of the high carbon foot print) than traditional concrete and with the addition of fly ash or slag (industrial waste products) the reduction can be as much as 35-40%.

-Results from the field show high levels of long term performance with minimal maintenance for most applications.

-Given it’s 30-50 yr lifespan, and the fact that it can be crushed and used for base after that, the life cycle cost of pervious concrete is actually lower than asphalt.

To DavidPopoffCt: While I am in CA where frost heave is not an issue, I do know that pervious is seeing wide acceptance in the upper mid west and even Canada. I suspect the deeper/thicker layer of sub base rock used in those areas goes a long way towards reducing heaving issues.

David

4 Kevin Earley December 9, 2010 at 9:19 am

Nice summary, I like the way you classified the permeable pavement options. Couple of thoughts:
Pervious block pavers are not more expensive compared to the other options they are readily available throughout the country and they can be machine installed. Plow damage is actually rare since most have chamfers and are installed on a leveling bed. Light color pavers have SRI values > 29. Surface infiltration rates exceed 300 in.hr when tested by ASTM C1701. A good resource is http://www.icpi.org.

Another type of product not mentioned – castellated concrete grid – these waffle-like units have 75% surface opening and are steel-reinforced – see http://www.checkerblock.com for an example.

Plastic grid, although high on recycling content, is manufactured in one or two locations and loses the locally manufactured LEED credit – the carbon footprint to ship it to your project might be noteworthy. They are not cheaper than concrete pavers. Also, these products are easy to damage and be removed – I would be careful with them in heavy loading commercial applications.

5 David Liguori December 9, 2010 at 1:29 pm

The installed cost of Pervious block paver”s, at least in my area, is actually higher than pervious concrete (PC) as there is more labor involved and the material cost per sq/ft is higher (3-$5 for pavers vs 2-$2.5 for PC). The machine installation method is only cost effective on very large commercial projects, at which point the numbers might shift in their favor.

In addition, because of the large gravel filled spaces between the pavers I am finding that municipalities and commercial developers are rejecting pervious pavers as “non wheel chair friendly”. Of course this is not an issue on most residential applications, and if the homeowner does the paver installation him/herself (not practical w PC) they would likely realize a nice cost savings.

6 Frank Sherman December 9, 2010 at 2:42 pm

For projects that have both residentia offstreetl parking and a common driveway you may need a hybrid solution. Keep in mind that there will always be the occasional heavy vehicle in the common drive portion of the site, think garbage trucks or fire trucks. Knowing how garbage will be handled for the project will give you solutions for that type of vehicle, but check City regulations about access drive requirements for emergency fire appartatus.
You may discover you need a fire lane with a certain type of surface and parking spaces with another surface solution. Think about adding bio swales to the mix and understand how water will move across the topography of your site. All of these approaches working in concert should give you a viable stormwater management solution.

7 Kevin Earley December 10, 2010 at 8:05 am

Permeable paver blocks do not get damaged by snow plows – they have chamfers to ease transition and are set level on a bedding layer to construction tolerances. Regarding frost heave – all permeable pavement systems with open-graded aggregate have porosity or air voids in the 40% range. This accomodates any potential volume expansion due to freezing. Frost heave issues apply to soils or processed stone (roadbase) with silt content. These systems should use drainage stone without any silt content.

8 Rob December 13, 2010 at 11:27 pm

Hanover Architectural Products makes a more attractive (IMO) pervious paver

http://www.hanoverpavers.com/residential/html/ecogrid.html

Also food for thought, any grass that is going to be continually parked on will not be grass for long.

9 Alex Gore December 15, 2010 at 11:11 am

im wondering how reliable the Plastic Grid Systems is over the long hall.

10 Kevin Earley December 15, 2010 at 12:52 pm

Alex – in my opinion – plastic products have properties that make long-term use suspect. For example, plastic properties can creep and can move due to temperature (thermal expansion). Plastic properties that include recycled rubber can retain heat and even ignite (tire chips are combustible so are some of these products). Most importantly there are NO ASTM or industry-defined standards for the manufacturing or installation of these plastic grid pavement products. On commercial projects, it best to stick to materials that conform to ASTM or a nationally-recognized association like: ICPI, BIA, NRMCA, NAPA, etc.

11 Fred December 17, 2010 at 5:18 pm

I really like the idea of vegetation growing in all the open spaces between the pavers (in whichever form) but if I use that system for a driveway or small parking lot, I wonder if it’ll be a tough job when winter comes along and I have to shovel the snow off it with all the tufts of grass sticking up.

12 christopher February 3, 2011 at 8:44 pm

Pavers are one of the most expensive per sf. surfaces you can install on a driveway but you cant beat it for beauty. I have seen grass between pavers work well but you must have a solid root structure with a material that holds enough moisture to keep it green, otherwise the grass dries out quickly and with hot summers it dies quickly. But i love the look.

13 jon February 25, 2011 at 3:10 pm

Nice grouping of porous pavers.

Plastic grids can be engineered to serve as fire lanes and emergency access drives. So they can handle heavy loading, at least occasionally. Sub-base engineering and compaction will be critical to its success, as for most other products.

I’m a little surprised that you didn’t look at gravel and stone dust, which can be the least expensive options of them all. Though they do need some periodic maintenance.

You can also use regular brick and paving stones, but space them with blocking or shims to provide drainage openings. This will duplicate the specialty shapes with far less material cost, and enlarge the patterns and array of materials you can use.

Perhaps a better way to do stormwater management is to slope your drives and walks so that stormwater is channeled to landscape or pond areas where it can form detention basins and soak into the soil over time. This would allow you to build a conventional drive at lower cost, and invest more in plants and landscaping, while solving the problem.

14 Mike February 28, 2012 at 6:09 am

Gravel and stones are good because they are inexpensive and help reduce project cost. Plastic is also good but gives out gases during heat.

15 rajiv puri September 25, 2012 at 3:05 am

try Modi pavers – they are like lego for driveways. easy to install – modular and therfore easy to change or fix. similar to the one above but also allows for gravel finish for those who do not wish to mow their lawn

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