Permeable Pavers

Permeable interlocking concrete pavement is designed to be as porous as possible, allowing water to adequately flow into an aggregate base, preventing flooding.

Commercial Solutions

We are proud of the reputation we’ve built as one of the leading commercial paving companies operating anywhere in the Carolinas or the surrounding areas today.

Municipal Solutions

Creating an innovative sustainable and ecologically friendly environment through low impact development, reducing major problems such as flooding and erosion.

Residential Solutions

Breathe new life into an outdoor area of your home using pavers, brick, stone, granite or permeables. We’ll guide you through creating the space of your dreams.

Permeable Solutions

Control storm water before, during and after extreme weather events as well as improve overall water quality thanks to the imbedded filtering system with Permeable Solutions.

Value Engineering

During projects, we provide better, more organized processes and procedures in an effort to better eliminate unnecessary costs that are discovered within the industry.

Products

Explore our paver products for concrete pavers, retaining walls, permeable pavers, sealers, joint stabilizers & accessories, clay pavers, natural stone pavers, slab & roof systems & porcelain tiles.

FAQs

Explore Unit Paving's Frequently Asked Questions

Permeable Pavers FAQs

Permeable Pavers from Unit Paving

Permeable interlocking concrete pavement (PICP) consists of manufactured concrete units that reduce stormwater runoff volume, rate, and pollutants. The impervious units are designed with small openings that create permeable joints. The openings typically comprise 5% to 15% 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. The picture shows installed pavers in a Seattle, Washington residential neighborhood. PICP significantly reduces the total amount of impervious surface and runoff.

How is a PICP surface cleaned and how often?

The openings in the surface of PICPs will require periodic removal of detritus 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 detritus 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.

A North Carolina State University study has shown that the initial surface infiltration rate of PICPs can be as high as 2,000 inches of rainfall per hour. For reference a 100 year storm may produce 4-8 inches per hour with 43 inches over 24 hours holding the record for the greatest one-day rainfall in the US. Per ASTM standards, a permeable project Unit Paving installed 3 years ago still has an average infiltration rate of 175 in./hr. That is 30 times greater than the 4-8 in./hr a 100 year storm may produce. We expect the system to maintain greater than 100 in./hr for many years to come.

Other research has shown that near initial surface infiltration rates can easily be restored through cleaning and replacement of the initial 3/4 to 1 in. (18 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.

Is there any benefit to using PICPs on low-infiltration soils such as some types of clays?

Yes. If soil infiltration is slow (generally under 0.5 in./hour or 4 x 10-6 m/sec), perforated plastic pipe drains at the bottom of the base can remove excess water while still allowing some of the water to infiltrate into the soil. Digging trenches up to 4ft deep into the soil often allows access to soils with infiltration rates up to 100 times greater than those found at the surface. 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.

Does the surface 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 well does the pavement perform in freeze and thaw conditions?

PICPs have been in service for years in freezing climates and have performed very well. 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. Freeze thaw cycles throughout the southeast are limited due to the lack of deep freezes and snow melts compared to northern climates. The southeast

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 reduces dependency on deicing salts as it eliminates ice from forming on the surface with the added benefit of reducing salt contamination in the 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 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.

Should a dense-graded or open-graded aggregate base be used under PICPs?

An open-graded base is standard use for permeable pavers because it has water storage capacity (void space between the aggregates) of typically 30% to 40%. Open-graded bases will vary in thickness due to water filtration needs and overall design parameters. The stones in the base course range from 2-6 in. (50-150 mm) in size. The bedding stone is used directly under the concrete pavers and is ¾ in. (18 mm) stone. The bedding stone depth is typically 1-2 inches but should never exceed 4 inches to minimize lateral shift down the road. The ¾ in. (18 mm) stone is also used as the joint filler between the permeable pavers. The base course and bedding material maximize storage, filtering, and treatment of pollutants in stormwater runoff entering the pavement surface. Open-graded bases are preferred because of the storage and waste water treatment benefits.

Interlocking Concrete Pavers FAQs

Why use interlocking concrete pavers?
Concrete pavers are produced on specially designed machinery which ensures an exact quality controlled process that produces paving brick of higher strength and durability than poured in-place concrete. Concrete pavers are manufactured as a single homogeneous mix throughout; not a two mix system which has a top coat. Concrete pavers have a minimum average compressive strength of 8,000 psi, compared to poured-in-place concrete with an average of 3,000 psi (almost 3 times stronger), and have a lower absorption rate as well. Concrete pavers are the ideal product for freeze/thaw environments. With proper installation, this product provides a hard wearing and flexible surface. The joints between the pavement allow the walkway, driveway, or patio to move without cracking. In addition, they can be “unzipped” to allow for repairs or easy access to utilities. Unlike asphalt, pavers are virtually maintenance free and do not need to be regularly sealed or replaced.
Why are they called “interlocking pavers?
It is the combination of the installation system, together with the ratio between the thickness and the length and width of the paver which makes them “Interlocking” – not the shape. When installed correctly over a base designed and properly prepared for the type of application and load bearing which the installation is intended to carry, the combination of the paver, bedding sand, edge restraint and joint sand causes them to interlock, allowing the individual pieces to work as a unified, flexible pavement.
What are the components of an interlocking concrete pavement?
The components include a base, bedding sand, concrete pavers with sand in their joints, and an edge restraint to contain the pavers at the perimeter.
How does the interlocking system work?
Pavers are placed over a leveling course, which is over a compacted aggregate base. The thickness of the base will vary depending on the purpose of the application. The pavers are retained at the outside perimeter of the project using edge restraints. Edge restraints such as plastic edging and concrete curbs are recommended. Once the pavers are placed and restrained, the interlocking process may begin. Coarse, angular sand is swept into the joints and over the pavers. The pavers are compacted and may take 1 or 2 passes before the full interlock can be achieved. After compaction, the project is ready for use. Sweeping and cleaning of the area will be necessary.
How do pavers compare with “Patterned” or “Stamped” concrete?
Patterned concrete pavements are merely large sections of poured-in-place concrete that have been embossed with a design. Therefore, they are prone to the same problem freeze/thaw cycles (ie. cracking and spalling), lower strengths and higher absorption rates as poured-in-place concrete. Pavers permit a flexible, breathable surface, working with nature. In addition, stamped concrete requires expansion joints every 10 feet or so, which can be very distracting. Also, patterned concrete pavements don’t allow access to underground utilities or the ability to make repairs. At practically the same price per square foot installed, pavers are clearly the best choice.
How long will my installation last?
Installed properly, pavers will out perform poured-in-place concrete, stamped concrete and patterned asphalt by many years.

How long will it take for my project to be installed?
Less time than you might think. The average home patio can be installed in a day or two. Unit Paving’s crews are experienced and efficient. Being a mortarless system, a lot of extra work and mess are eliminated.
After installation, will weeds grow from underneath my patio or driveway?
Once complete, the installation will not permit seeds to germinate from beneath the pavers. However, weeds and grass could result from seeds or spores blowing into and lodging in the joint sand. If weeds do appear, a spot vegetation killer can be used seasonally and will not damage the pavers.
Will the colors fade from the pavers?
Pavers are made with the highest quality pigment and have color completely throughout each unit. However, the extreme effects of the sun and elements work against all building materials. Over the years, it is possible to see the colors mellow as they age.
Can I add on to my project at a later time?
One great reason for using pavers is because you can easily add to any type of project that you are doing. All you need to do is to take up the existing edge restraint and a few rows of pavers. Prepare the base and setting bed for the new section. As you add the new units, blend the new brick with the old of the existing section. This will help reduce any variance of the existing colors.
Should I seal my project?
Pavers are manufactured to be durable. Therefore, the use of a protective sealant is optional and a matter of personal preference. A sealant will make stain removal easier, might minimize weed germination in the joint sand and can enhance colors. Sealers, however, are a topically applied product and must be reapplied every 3 to 5 years. Sealing pavers may make pavement slippery when wet. Before sealing, the installation must be thoroughly cleaned and completely dry. Be sure to use sealers specifically for concrete pavers. More intense use of the pavers and extreme climates often increases the frequency for re-applying a coat of sealer.
What about stains on my installation or any areas that may become damaged?
Stains can be removed with appropriate cleaning products. However, should a severe stain or severe damaged occur, pavers  may be flipped over or individually replaced.
Can I install pavers over an existing concrete walkway or patio?
While this is not the preferred method, your installation can be laid over top of existing concrete walkways, providing there is not substantial heaving in the existing area. Several other issues need to be addressed. First, the grade will need to be raised by about 3″ (the thickness of the bricks plus bedding sand or bonding agent). This is particularly critical if any doorways are involved. Second, remember that if the existing concrete slab should raise or drop with freeze/thaw conditions, the bricks will do the same.
How can I remove snow without damaging the installation?
For most residential applications, conventional methods of snow removal are acceptable (ie. shoveling or snowblowing). Care should be taken to make sure the skid plates are set to maintain a clearance between the snowblower and the bricks so as not to scratch the bricks. Please note, the use of heavy snow removal equipment may damage your brick or the installation. Ice melting chemical products which do not contain calcium chloride are recommended for use.
What is the white film on my bricks and will it go away?
The white film, known as “Efflorescence”, is normal for masonry products and it may appear on the surface of the pavers. It may not occur at all. If it does occur, it is not permanent and will disappear over time. It may appear randomly or only in certain areas. It is a natural occurrence from the cement hydration process. Calcium oxide from the cement reacts with water inside the bricks and forms calcium hydroxide. This seeps to the surface and reacts with the carbon dioxide in the air to form calcium carbonate, a whitish residue. When moisture on the surface evaporates, it becomes visible. It will wash off or wear off over time. If you wish to speed up the natural process, there are cleaners available that are designed to remove efflorescence.
Is it okay to use fabric designed to prevent weed growth in plant beds instead of geotextile?
No, this material is sometimes not as strong as geotextile and can tear easily.

What is geotextile? What does it do? Is it necessary?
Sometimes called filter fabric, geotextile is made of plastic threads that allow water to pass around them, but not very small particles of soil beneath them. Geotextile separates and contains the base from the underlying soil subgrade. It allows the base to shed water, and prevents the soil around it from working its way into the base. Without geotextile, the soil will work its way into the base and weaken it. This is a slow process that happens when the soil is saturated with water or during periods of thawing. Geotextile stops this process and extends the life of the base by many years. Geotextile is recommended for use over silt and clay soils. It is not essential in sandy soils.

What is the base made of? What kind should be used?
The base is typically made of compacted, crushed stone that varies in size from one inch (25 mm) down to dust. Base materials used under asphalt street pavements are acceptable for use with interlocking concrete pavements. Some parts of the country use cement stabilized or concrete bases due to very weak or slow draining soils. However, most applications use a crushed stone base that’s compacted. Without geotextile, the soil will work its way into the base and weaken it. This is a slow process that happens when the soil is saturated with water or during periods of thawing. Geotextile stops this process and extends the life of the base by many years. Geotextile is recommended for use over silt and clay soils. It is not essential in sandy soils.