Frequently Asked Questions about Permeable Pavers
Here are some of the most common questions that we get for our
permeable paving systems. If you have a question that isn't
covered here, please contact our Customer Service Department.
- What are EP Henry ECO™ Permeable Pavers?
- EP Henry ECO™ Line of Permeable Pavers are a collection of permeable interlocking paving stones which allow water to infiltrate back to the subsoil, preventing stormwater runoff and potential pollution of our streams and waterways.
EP Henry’s ECO Line includes a variety of shapes, colors, patterns and textures including: Eco Cobble®, Coventry® ECO Cobble, ECO Paver and more. They are Permeable Interlocking Concrete Pavements (PICP) and are considered a Best Management Practice (BMP) for stormwater management.
- What are some of the features and benefits of EP Henry ECO Line of Permeable Pavers?
- EP Henry ECO Cobble® and Coventry® ECO Cobble® offer beauty, function and cost savings in sustainable design. Available in multiple colors, sizes, textures and patterns, they also integrate seamlessly with our non-permeable Old Towne Cobble™ and Coventry Stone I ® pavers — thus providing you a wide variety of options to meet your design, budgetary and environmental requirements. And, we offer them in 6cm as well as 8cm thicknesses so you don’t have to over-design — or overpay — where your project does not have heavy vehicular requirements.
- Why Choose Permeable Pavers?
- Fortunately, the growing awareness of and the need for sustainable environmental practices has fostered the development of technologies designed to lessen the harmful effects of stormwater runoff. A hardscape built with EP Henry ECO Permeable Pavers is a prime example. Once installed, it benefits the environment by reducing the amount of stormwater runoff - along with the accompanying soil erosion and water-born contaminants and pollutants carried with it. They also allow water to filter back into the soils directly on site and replace ground water and recharge local aquifers.
- What is permeable interlocking concrete pavement?
- Permeable interlocking concrete pavement (PICP) consists of manufactured concrete units that reduce stormwater runoff volume, the rate of flow, and pollutants. The impervious units are designed with small openings that create permeable joints. The openings in EP Henry Permeable Pavers are 7% and 10% of the paver surface area and are filled with highly permeable, small-sized aggregates.
The joints allow stormwater to enter a crushed stone aggregate bedding layer and base that supports the pavers while providing storage and runoff treatment. PICPs are highly attractive, durable, easily repaired, require low maintenance, and can withstand heavy vehicle loads. PICP significantly reduces the total amount of impervious surface and runoff.
- Can EP Henry ECO Permeable Pavers be used for driveways and roadways?
- Yes. EP Henry ECO Permeable Pavers come in 8cm (for more heavily trafficked areas such as commercial parking lots, building complexes and streets) and 6cm (for light vehicular trafficked areas such as residential driveways).
- What intensity and duration of storms can be managed?
- It depends on the amount of water that drains onto the PICP, the depth (and storage capacity), the base, the infiltration rate of the soil under an open-graded base and the presence of drain pipes within an open-graded base. PICPs are intended to manage water quantities and pollutants from smaller, more frequent storms such as those with a return period of 10 years or less. These storms tend to be shorter in duration and often have the highest concentrations of pollutants. PICPs are not intended to control flooding from larger, infrequent rainstorms.
- Does PICP improve our water quality?
- Because rain water run off carries with it many pollutants the filtering done by the base helps reduce many pollutants including Nitrogen and Phosphates, which are the biggest threats to our clean water.
- How well does the pavement perform in freeze and thaw conditions?
- PICPs have been in service for years in freezing climates and have performed adequately. Many projects throughout Canada, the northern U.S., the United Kingdom and Germany speak to the durability of these pavement systems in cold climates and their ability to accept snowplows and salts without paver damage. In order to ensure high durability in freezing climates, the paving units should conform to the requirements of ASTM C 936 in the U.S. or CSA A231.2 in Canada. Both of these product standards include tests for freeze/thaw durability.
When the sun and temperature are right, ice and snow on PICPs can melt and immediately soak into the pavement surface. Water does not collect on the surface and re-freeze. This reduces slipping hazards.
Sand should not be used for foot or tire traction on PICP. Deicing salts can be used. After plowing, melting of any remaining snow can occur if the temperature rises above freezing. This will help eliminate ice from forming and reduce salt contamination in groundwater.
Water in the base typically should drain within 24 hours. It's unlikely that ice will form in the base within this time period should temperatures drop below freezing. If the water does freeze before draining, there is adequate space for the ice to expand within the open-graded base, thereby minimizing the risk of heaving. Should soil heaving occur, the pavement surface is flexible and should not be damaged from minor upward movement or from resettlement during a thaw.
- What is the load capacity of these systems?
- Eco Pavers and 3-1/8” Eco Cobble Pavers are suitable for heavy vehicular traffic. The stone base for any heavy vehicular application must be designed and constructed in a manner suitable for that kind of heavy traffic use. The Eco-Cobble permeable paver system satisfies the requirements of meeting or exceeding an H-20 or HS-20 loading. The subgrade soil and base preparation are critical to the performance of any pavement or paver system subjected to vehicular traffic. Eco Pavers and Eco-Cobble are capable of supporting heavy vehicular design loading, but it is up to the design engineer to ensure that an adequate base thickness is specified and that verification of subgrade soil occurs prior to installation of any paver product. All pavement design is site-specific based on actual soil conditions and anticipated vehicular loading patterns.
- How much do these systems cost? By percentage, how much higher is this method than a typical urban street cross section?
- The cost of a PICP installation will vary depending upon the price of materials required to build that kind of system. That cost may be as much as 35% to 50% more than a standard paver installation depending upon the design of system. The least expensive is usually a full exfiltration system. A non-exfiltration system is usually more expensive because of the liner under the base stone that prevents collected storm water from seeping directly into the ground at that location. Other structural elements such as the edge restraints and highly permeable geotextile may be more expensive than similar materials used in standard paver jobs.
- Permeable vs. Asphalt?
- Unlike traditional Asphalt and Concrete, EP Henry Permeable Pavers allow rainwater to naturally filter and return to the ground, instead of collecting pollutants and debris while flowing into sewers, local streams and waterways. EP Henry Permeable pavers permit water absorption into the soil, which reduces runoff flooding and erosion, lessens the impact and stress on existing local storm sewer systems through reduced peak discharges. In addition EP Henry Permeable pavers are winter-friendly…snow melt drains via paver joints, reducing slippery, icy surfaces and the need for harsh deicing chemicals and can be excavated for underground utility repairs, if needed, and reinstalled with no "patch" appearance and no loss of permeability. * May qualify for tax credits and water bill savings
- Should a dense-graded or open-graded aggregate base be used under PICPs?
- An open-graded base is most commonly used because it has water storage capacity (void space between the aggregates) of between 30% and 40%. The stone sizes in open-graded bases can be as large as 3 in. (75 mm) and as small as 1/4 in. (6 mm).
There is typically a thinner layer of small stone sizes (6 mm to 1 mm) used for bedding directly under the concrete pavers. The bedding and base bedding material maximizes storage, filtering, and treatment of pollutants in stormwater runoff entering the pavement surface. Open-graded bases are preferred because of the storage and treatment benefits.
- Is there a benefit to using PICPs on low-infiltration soils like clay?
- Yes. If soil infiltration is slow (generally under 0.5 in./hour or 4 x 10-6 m/sec), perforated plastic pipe drains in the base can remove excess water while still allowing much of the water to infiltrate into the soil. The drainage rate for the water contained in the base is typically no greater than 24 hours.
Over practically impervious soils or high bedrock, an impervious pond liner can be used to detain, filter, and release the water through drain pipes. Regardless of the rate of soil infiltration, the filtering action of the open-graded base can reduce water pollutants. All permeable pavements require periodic surface cleaning.
- Is there any recycled content available in these materials?
- EP Henry unit concrete products contain recycled materials thereby reducing the need for the use of additional new raw materials and the consumption of fossil fuels to transport them.
- How is PICP being viewed by state and local government agencies?
- Based on recent data provided by local conservation consultant groups, in 2013 and moving forward, localities will be required by state government to have storm water management ordinances in place including acceptable BMP’s like Permeable Paving as options for reducing run-off and pollutant discharges into our watersheds.
- Can I use PICP as part of a LID (Low Impact Development)?
- Yes. The benefits of incorporating PICP into a LID instead of traditional SWM, include: reduced TSS, TN and TP Loads, ground water recharge and reduced volume runoff. Also reduces or eliminates need for unsightly retention basis.
- Do ECO Permeable Pavers conform to the Americans with Disabilities Act (ADA) requirements?
- Yes. ADA Design Guidelines require that surfaces be firm, stable and slip resistant. PICP designs can provide a firm and stable surface for visually impaired persons and those using wheeled mobility devices. If the openings in the surface are not desired, solid units can be used in areas subject to disabled persons. Such areas might include designated spaces in parking lots.
ADA recommends that the static coefficient of friction for flat surfaces along accessible routes be 0.6 and 0.8 for ramps. ADA advisory material recommends various test methods to assess surface slip resistance. PICPs can meet slip ADA resistance requirements using test methods recommended in ADA advisory literature. For additional information on these requirements, see ICPI Tech Spec 13 - Slip and Skid Resistance of Interlocking Concrete Pavements.
- How is a PICP surface cleaned and how often?
- The openings in the surface of PICPs will require periodic removal of debris and sediment trapped by the small sized crushed stone. Dirt is typically removed by a vacuum-sweeping street cleaning machine.
Cleaning is done when the pavement surface and loose material remnants are dry and can be loosened by sweeping and vacuuming. The frequency of cleaning will vary with the use of the pavement and position of sediment, leaves, etc. from adjacent areas. Cleaning should be done on an as needed basis generally not more than once a year. The surface should be monitored during the early life of the pavement so that a regular cleaning schedule can be established.
A North Carolina State University study has shown that the initial surface infiltration rate of PICPs can be as high as 2,000 in./hour (5,080 cm/hour). Other research has shown that near initial surface infiltration rates can be restored through cleaning and replacement of the initial 3/4 to 1 in. (20 to 25 mm) depth of small stones in the openings of PICPs. For highly clogged pavement openings, the stones can be removed with vacuuming and replaced with clean material. This is a distinct maintenance advantage over pervious concrete and porous asphalt pavements.
- Are EP Henry’s ECO Permeable Pavers eligible for LEED Credits?
- Yes, based on the current U.S. Green Building Council guidelines, points can be achieved for using EP Henry concrete paver products in several categories including: stormwater design – rate, quantity, and treatment; heat-island effect (non-roof); regional materials, recycled content, and innovation in design.
EP Henry ECO Line may qualify for LEED credits under:
1. SS Credit 5.2 Site Development: Maximize Open Space
2. SS Credit 6.1 Stormwater Design: Quantity Control
3. SS Credit 6.2 Stormwater Design: Quality Control
4. SS Credit 7.1 Heat Island Effect: Nonroof
5. MR Credit 2 Materials and Resources: Construction Waste Management
6. MR Credit 3 Materials and Resources: Material Reuse
7. MR Credit 4 Materials and Resources: Recycled Content
8. MR Credit 5 Materials and Resources: Regional Materials
9. ID Credit 1 Innovation in Design
10. RP Regional Priority Credits