What is permeable paving and where are they used?
Permeable pavements – where they can be used?
Did you know that permeable pavements first came to light in the 1800s?
Read on to know more!
Permeable pavement refers to a surface that is porous in nature so that the rainwater falling on the surface or surface water run-off penetrates into the pores whereby it is stored in a reservoir before being infiltrated into the soil.
These permeable pavements are usually made up of concrete or asphalt or open-pore pavers that consist of a stone reservoir underneath.
They are mostly used in sidewalks, low-traffic roads, driveways, parking lots, residential roads, patios, swimming pool decks, well linings, and low-water bridges.
They are also used to trap pollutants and solids thereby preventing them from polluting the water.
Did you know?
Permeable pavements first came into light in the 1800s in Europe and they were used for structural purposes like pavement surfacing, infill panels, and load-bearing walls. They gained popularity again overseas after the second world war as there was a scarcity of cement.
Usage of permeable pavements produces surface cooling at the surface or below the surface whereas traditional pavements produce surface heating.
In cities where there are extremely high temperatures in summer, permeable pavements are beneficial.
What are the types of permeable paving?
Learn more about the different types of permeable paving and their advantages and disadvantages.
There are different types of permeable pavement construction as described below.
- Porous bricks
- Gravel, stone aggregate, and shells
- Open-joint bricks
- Open paving patterns
- Grass-concrete pavers
- Woodchips and pine bark
- A mixture of gravel and grass
- Natural stone
- Composite resin
1. Porous bricks
Porous bricks allow air and water to pass through the porous grain structure on the porous bricks.
They could be used in roads, footpaths, and cycle paths. However, they tend to become clogged by sediments in the process.
2. Gravel, stone aggregate, and shells
On porous foundations, stone aggregate or gravel with an average grain diameter that is consistent could be used.
These gravel and stone aggregates could be used on cycle paths, footpaths, or car parks which are less intensively used.
The purpose of using shells is to be used as a loose covering layer or to be embedded in clay or sand.
These materials could require more maintenance when they are used on less solid foundations.
For more stability, stabilization mats could be used to retain the shape of the material and to use on less solid foundations.
These types of pavements can be used in footpaths, center beams, playgrounds, fire access roads as cover layers in private gardens, and pavements.
3. Open-joint bricks
When open-joint bricks are laid on the pavement, there is always a gap between the bricks, and these joints remain open.
The disadvantage with these types of open-joint bricks is that the gaps can eventually become clogged with sediments.
4. Open paving patterns
The laying of ordinary bricks in open or semi-open patterns. Soil, grass, shells, or gravels could be used to fill the open spaces.
By varying the brick pattern, the quantity of open space could be determined in the pavement.
These open paving patterns do not support heavy loads.
5. Grass-concrete pavers
Large open spaces could be found in between the tiles in these types of grass-concrete pavers.
These grass-concrete pavers could be used on roads, garage drives, and car parks that are less intensively used.
They are not stable and grass does not sufficiently in more intensively used spaces.
6. Woodchips and pine bark
Woodchips and pine bark are natural bark that allows water and air to pass through them.
They can be used in garden paths and playgrounds.
They are an alternative to weed killers as they do not allow the vegetation to grow.
After a few years, these woodchips and pine bark have to be topped using a new material.
7. A mixture of gravel and grass
A mixture of humus and stone aggregate or gravel can be used on the surface in a stabilizing mat.
On the top layer, the grass is sown, and then it is compacted.
Concrete is highly suitable for larger projects where large amounts of material are required. It is cost-effective.
It comes in a wide variety of textures, colors, range depths, and shapes.
Installation is easy and the lifespan expected is over 20 years.
However with time, cracks develop, and in cases of colored concrete, the hue would fade in some years.
9. Natural stone
Owing to the cost of natural stone pavement, a significant amount of value is added to the property.
Maintenance is easy as it requires only simple cleaning.
It is highly durable and the color is not expected to fade as in the case of concrete or other man-made varieties.
On the other hand, the cost incurred would be high but it also adds a significant amount of value is added to the property.
Natural stone pavement is advisable to be laid only by experts as any damage or error might incur huge costs.
When using brick, the block paved area looks uniform. Installation is easy and it is also highly slip-resistant.
A significant amount of maintenance is required as grass could grow in between the cracks.
When the sub-base is not layered correctly, the weight of cars could create dips in the brick.
When the bricks are thinner, they can be broken easily while they are compacted.
Pavers are available in patterns. The color is not likely to fade over time. It is hard-wearing and slip-resistant.
Maintenance is required as it might be exposed to moss growth.
Fitting could look awkward as sizes may be varied by millimeters per block.
Per block cost is high as it is not as easy to find as concrete.
Block depths might be less and clay could be harder to cut.
12. Composite resin
Rainwater would not pool on the surface as composite resin is permeable.
It is eco-friendly, installation is easy and cost-effective.
Composite resin is a water repellant. There will be no drainage issues with composite resin as with concrete.
As the material is smooth, there might be potential slip hazards and moss growth.
What are the potential benefits and disadvantages of using permeable paving?
Check out the potential advantages and disadvantages of using permeable paving!
- By using permeable pavements, hydrological balance is restored and runoff water quantity is reduced. It reduces the high rate of water discharge through the stormwater system. The runoff speed is also greatly controlled.
- The physical amount of pollutants can be reduced could be reduced by using the permeable pavement. In biological ways, the plants that are found between the permeable pavers can collect and store pollutants. Chemically, bacteria could be used in breaking down pollutants.
- Permeable pavements could slow down the process by reducing the urban temperature thereby the amount of stress on lakes is highly reduced.
- By using permeable pavings, runoff can be controlled at the source and groundwater recharge is done.
- The need for having water retention basins and collection areas is reduced.
- On financial aspects, the cost of installation and curbs, gutters, retention basins, water collection installations, etc are very less or nil. Life-cycle costs are less while the life expectancy is equal to that of regular concrete.
- In winter, when compared to traditional pavements, permeable pavements require less de-icing products or salt.
- Permeable pavings also provide for local flood control and the quality of waterways on the surface is increased.
- Soil erosion is reduced and evaporative cooling is provided by permeable pavements.
- The regular stormwater infrastructure costs could be greatly reduced by using permeable pavings.
- The amount of snow-ploughing required is less and groundwater pollution is controlled.
- In due course, the permeable pavements could be clogged with sediments. To prevent blockage, regular maintenance would be required.
- Permeable pavements could be a failure when there are heavy loads.
- To remove snow, the salts that are used in cold climates could pass through permeable pavements which could contain chlorides.
- Maintenance costs incurred may be high.
What is the cost associated with permeable paving and what are the design elements?
There are three types of infiltration systems used in permeable paving namely no infiltration, partial infiltration, total infiltration.
Learn more about the cost associated with it and some of the design elements!
The cost associated with permeable pavements:
For an area of size up to 40 square meters, the cost per square meter would be £100.
For an area of size 40 to 100 square meters, the cost per square meter would be £85.
For an area of size 100+ square meters, the cost per square meter would be £75.
For blocks and edgings, the cost per square meter would be £950.
For sharp sand, the cost per square meter would be £150.
For kiln-dried sand, the cost per square meter would be £75.
For 3 x skip hire, the cost per square meter would be £450.
For additional supplies, the cost per square meter would be £350.
Totally, the cost would be £2,075 (£38 per square meter) excluding labor.
What are some of the factors that affect the cost of permeable paving?
Here are a few to consider.
- Choice of material
- Extra materials
Depending on the location of the property, costs may vary.
In London, the total cost would be £4,500 to £5,000.
In South, South West, and Midlands, the total cost would be £4,000 to £4,500.
In Northern England & Scotland, the total cost would be £3,500 to £3,750.
Complex paving designs cost more compared to simple designs as in most cases.
Instead of choosing an organic shape like oval or circle, if you prefer rectangular or square shapes, the prices may go up as it involves more labor.
When the size of the property is bigger, the cost incurred will be high as there would be an increase in the cost of materials and labor.
4. Choice of material:
Depending on the choice of material, be it Concrete Block Paving(CBP) or a natural stone, the costs would vary.
CBP comes with a range of sizes, shapes, and textures and it is easy to create any style when they are laid in particular patterns. For block paving, the most popular choice is CBP.
Natural stones provide a great return on investment while selling the property.
Preparing the ground before laying block pavers is a significant contributor to the overall cost of the project.
If your property is in need of some digging or leveling before laying permeable pavers, or if you have existing pavements that have to be removed before laying the new one, these will add to the overall costs.
7. Extra materials:
When a sub-base has to be prepared before laying the pavers, it adds to the extra cost.
This will require a sub-base, sharp sand, mortar, and a layer of soil. An anti-weed membrane can also be introduced to ensure the health and longevity of the paving.
Can you save money on block pavement?
To discard the labor costs, you may consider doing the block paving yourself which requires hard work and patience.
Here are some factors to consider before choosing to do the block pavement yourself.
It is advisable to start first with a small area, especially when you do not possess experience.
An ample amount of labor costs could be saved but doing the block pavement yourself consumes a lot of time and precision to a high standard is required.
After thoroughly excavating the surface, make sure to make the surface solid and level. In case something goes wrong, there might be dips at places where water collects, and paving blocks might be loose.
What are the design elements?
Concrete block systems that are permeable might need infiltration blocks and additional drainage or infiltration blocks alone either in the sub-base or at the surface.
Generally, projects that are less than 100 m2 can do with just infiltration based on the permeability of the sub-grade while large projects would need a combination of infiltration blocks and additional drainage.
The standards for the design of permeable pavements could be found in BS 7533:3 (2005 ed.) CIRIA’s Suds Manual and Interpave’s guide to Permeable Pavements.
The structure of permeable pavement is similar to that of block pavement which is as follows.
- Preparation of sub-grade
- Sub-base using a specific material
- A laying course with no-fines granular material
Based on the project parameters, geotextiles could be included in the structure.
A no-fines granular material is used to fill the surface void with infiltration paving.
The sub-base or geotextiles could be used to grasp the pollutants thereby preventing them from reaching and mixing with the watercourse.
Between the bedding layer and the sub-base, there is a geotextile layer that can be used to trap and decompose any organic matter in a normal way. It could also trap other pollutants and hydrocarbons before they reach the sub-base.
An impermeable membrane underlying the sub-base can store pollutants there from where they could be directed to a treatment facility.
The discharge pipe consists of an inert level that could be set either at the bottom of the sub-base layer or at the top of the sub-base layer.
When set at the bottom of the sub-base layer, all underground water would be drained.
When set at the top of the sub-base layer, the sub-base would retain a portion of the groundwater.
In tanked permeable pavement systems, if there is any contamination like diesel spillage, the contamination would be restricted to a limited area and it will not mix with the watercourse. In this case, the cleaning operation would be easy and cost-effective.
Inside the sub-base, hydrocarbons could be broken down using natural processes.
The breakdown process could be accelerated by applying oil digesting microbes on the permeable pavement.
To prevent the building up of pollutants to high levels, a dedicated treatment process is included in the system especially in heavily trafficked areas like lorry and car parking slots.
“Fully contained” projects are projects where pollutants and groundwater are corralled inside the system.
When there is a shallow water table or when the threat to water aquifers or resources, full containment is designed in the system.
Storage for future harvesting as ‘grey water’ can also be created using fully contained systems.
The pavements are generally of two types:
Porous pavements, which allow water to pass through them.
Permeable pavements, made of impermeable units where between joints, there are gaps.
There are three infiltration options available.
Option 1: Total infiltration
In total infiltration type, all water passes through the paving and gets infiltrated into the soil. There is no discharge from the system.
Option 2: Partial infiltration
In a partial infiltration system, there are pipes that are perforated at the formation level for removal of rainwater that otherwise could not be absorbed by the sub-grade.
Option 3: No filtration
The rainwater is captured on a membrane laid at the formation level. Using perforated pipes, the water is taken to an outlet. This system is highly useful when water is to be retained.
What are the maintenance aspects of permeable pavement construction?
It is important that permeable pavements are regularly maintained for optimum performance.
Read more about the various aspects here!
Because of the infiltration systems, the voids in the top 15-25mm are self-sealed with organic matter, slits, and muds.
Because of this, the capacity of the drainage could be reduced.
A reduction of around 10% of the theoretical maximum of the permeable pavement’s drainage capacity is assumed by the engineers.
Because of this, in order to cope with exceptional flows, additional drainage run-off is provided.
To keep the joints and voids clear, infiltration systems should be regularly jet washed.
But since it is a labor-intensive and expensive process, reduction in capability and silting is assumed in the design of the system over time.
In the case of porous systems, periodic brushing is required to clear the pores that are blocked.
Local conditions determine the jet-washing frequency.
When jetting is done regularly around 80% of the voids in the porous structure could be unclogged.
What are some factors to note while constructing permeable pavements and FAQs
Keep these factors in mind while constructing permeable paving.
Also, find answers to a few frequently asked questions here!
- There is a huge void content in pervious concrete and when compared to regular concrete, its overall strength is lower. So, for high-volume streets, heavy loading areas, highways, and potential spill sites, pervious concrete is not recommended.
- Some types of pervious pavements demand regular maintenance as pollutants may clog the pores which could lead to global warming and climate change of the planet. Pervious concrete will follow the characteristics of impervious concrete when proper flushing or vacuuming is not followed.
- When there is a 20% increase in the ground surface slope, stormwater has the potential to run downhill instead of being absorbed on the permeable pavement.
- Porous concrete might be expensive when compared to regular concrete or asphalt, but it would be neutralized as stormwater installations are not required.
- While designing a pervious pavement project, stormwater runoff volume should be carefully calculated which otherwise could stop the water to infiltrate into the ground.
Are permeable pavers expensive than traditional pavers?
When compared to traditional pavers, permeable pavers could cost more in the initial stages but you end up saving money in the long run.
Do permeable pavers demand regular maintenance?
Permeable pavers need to be maintained regularly for optimum performance. It is necessary to regularly sweep them, vacuum 4-times a year, and re-fill the voids when required.
Do you need planning permission to lay block paving?
Planning permission is not required for laying permeable concrete block paving in the driveway or front garden, according to official UK regulations.
in the case of impermeable blocks, water should be allowed to run to a suitable drainage area.
In cases where drainage areas are not suitable, planning permission is required for more than 5 meters squared of paving.
How long does block paving last?
When they are properly maintained, they can last more than 10 years.