As towns and cities grow and we pave, concrete or tarmac (asphalt) over more and more, there is less and less actual ground e.g. soil available for rain water to soak into and dissipate.
This water has to go somewhere and, in large quantities, can easily overwhelm drainage systems causing flooding and pollution. The solution is to create permeable driveways, patios and hard standings so water can pass through and soak into the ground rather than run directly into any drainage systems.
The options for permeable driveways, patios or parking on a front garden have increased significantly now that the problem has been recognised and the planning rules have changed to encourage this form of construction.
The Options for Removing Water from Driveways and Patios
There are essentially only three options for removing the rainwater that falls on to a driveway:
- Allow it to pass through the surface of the driveway and into the soil
- Carry it off to a soakaway or rain garden, where it can then be absorbed by the soil or removed without entering the drainage system
- Allow it to feed into the drainage system
The best solution is the one that does not overwhelm the drainage system and allows as much water as possible to be absorbed by the ground nearest to where it has fallen.
The ground conditions will determine what is possible, for example, clay soils do not allow water to pass through easily which makes them less suitable for solutions that involve absorption directly by the soil. In this instance you might have no choice but to use the drainage system.
In light of the above it is possible to use a range of solutions where one complete solution isn’t possible. Continuing the example above, when the ground can no longer absorb the rainwater during/after a heavy downpour, then the excess run off can be removed through the drainage system.
Now that we know the broad types of drainage options available we can examine the advantages and disadvantages of each specific types of driveway or patio.
If you would like to know more about the various different types of driveway construction then take a look at our different types of driveways project here.
Types of Permeable Driveway and Their Advantages or Disadvantages
There are several different approaches that can be used to create a permeable driveway and each uses a different set of construction techniques and materials. Here follows a run down on each of these and their relative pros and cons:
Reinforced Grass Driveway and Parking
These are either plastic or concrete grid systems, set down into the ground or led on top that reinforces it, stopping your wheels creating ruts but allowing the grass to grow between the mesh. Plastic systems can also be used to stabilise a gravel driveway (see below) and stop the gravel spreading away from the driveway.
They are easy to install and look very natural once the grass is established but you will need to use the recommended grass species that will grow up through the mesh. While this is the most natural looking and eco-friendly solution, it does require maintenance such as mowing.
If gravel is used this will need to be swept back in to the mesh on occasion, especially on sloping driveways.
On the whole, grass driveways are not really suitable if you car is parked there all the time as the lack of light will kill the grass. Also during the colder, damper months of the year, excess water can make the ground boggy causing your wheels to spin which will chew it up further.
Gravel or Shingle Driveways
Gravel driveways are very popular, largely because they are really easy to create, can be very attractive and are very effective as a permeable driveway. Find out here how you can lay a gravel driveway yourself. In summary, the gravel is laid over a prepared sub-base and weed mesh.
Along with it being cheap, easy to make and attractive to look at, a gravel driveway is very easy to maintain, especially if you have used a weed mesh to stop any unwanted plant growing popping through.
However, gravel is not really suitable for steeper driveways and can cause difficulty with wheeling objects such as children’s buggies, wheelchairs or the similar across it and also getting your car on to it as it can cause wheels to spin.
As we have mentioned, on the plus side maintenance is very easy and only involves sweeping any escaping gravel which scatters from time to time back on to the driveway and also just keeping on top of any weeds that appear.
Wheel Tracks for Driveways
This is where you only pave the area of your driveway where the wheels of the car will go. The advantage of this is that the rest of the driveway remains porous and permeable.
The paved tracks will need to be laid as normal (see here how to lay paving slabs), and the water should then run off on to the permeable ground surrounding it. Obviously any planning between the tracks needs to be low growing e.g. grass!
This is another cheap and easy solution, although it will require some maintenance to keep the planting between the tracks tidy. Planning permission will not be required so long as the total paved area is kept below 52m. Find out more about the planning restriction for driveways below.
Permeable or Porous Hard surfaces
There is a wide range of permeable surfaces that allow the water to pass through while still providing a sound hard surface for driving and parking on. Porous asphalt, concrete and block paving either allow the water through the material or around the edges of the blocks, however they have to be built on a porous sub-base.
Surfaces such as these are very durable and require a minimal amount of maintenance and the bonus is you will still have the look and feel of a normal paved area.
The choice of materials, styles and finishes for such hard standing surfaces is huge, with a finish sure to suit any tastes.
The one big drawback with hard standing surfaces such as these is that the construction in more complex and therefore much more expensive and you will likely need a contractor that has experience in laying such structures – which you can find here.
Building a Soakaway or Rain Garden
In some instances it is not possible or practical to have a permeable driveway so a traditional impermeable solution will need to be used.
Additionally in some cases the porosity of a given drive surface is not enough to cope with heavy rains and due to this will lead to a great deal of excess runoff, for example if the driveway is on a steep slope.
In this situation as we have mentioned, you can’t use gravel as it will cause other issues and the other option of a porous hard surface simply won’t absorb all the rainwater before it runs off,
Also if you happen to be on a clay soil, which is very slow to absorb water, even if your driveway in highly permeable the water will not be able to pass through the soil quick enough so with back up and puddle on top of the drive in a heavy downpour.
The solution to these scenarios is to create a “trap” or “sink” of some sort where any excess water can collect and then drain away into the ground (or be used elsewhere) over a longer period of time. There are essentially three solutions that you can use:
- A Soakaway
- A Rain Garden
- Rainwater Harvesting
All these solutions can deal with either the excess water from a permeable driveway, or they can be used with a traditional drive construction. All the runoff water should be channeled to them to be absorbed or removed, meaning that it does not end up in the drainage system.
Here are the relative advantages and disadvantages of each solution:
1. Using a Soakaway to Absorb Excess Water From Your Drive
A soakaway is essentially a large hole in the ground which is filled with large and course aggregate where rain water collects and then slowly seeps away down into the soil.
We have a whole project on the construction of a soakaway, so we will not get into it here, but see the project for full instructions on how to build one.
The advantage of a soakaway is that it is relatively cheap and easy to construct and can, in the right conditions, absorb significant amounts of excess water.
While the construction is relatively easy, it is a significant project which requires the excavation of a very large and deep hole. If not constructed properly they are not as effective and can even make issues worse!
One point to note is that you cannot use a soakaway if you have a clay soil (clay, silty clay or sandy clay) as the water simply fails to drain quick enough and can cause huge issues down teh line.
2. Absorbing Excess Runoff in a Rain Garden
One way to think about a rain garden is that it is an open soakaway with plants planted in the top to help absorb the excess water.
Depending on the requirements and amounts of water that needs to be dealt with, they can be constructed as a depression in the ground where excess water is channeled which in turn is then planted with suitable plants or laid with cobbles to slow the runoff and allow it to be absorbed by the vegetation.
For more information about rain gardens and how to build one, have a look at the Royal Horticultural Society website.
A rain garden can be a low ecological impact and highly attractive feature for your garden, almost like a pond!
If you have the space and with the right soil conditions they are very effective and absorb significant amounts of water. However there is be a fair amount of work involved in terms of construction and it is important to have an understanding about the soil and plants that should be used.
3. Rainwater Harvesting
In its simplest form this could be a water butt collecting water for reuse later, say for watering the garden or washing the car.
A more complex solution would involve underground tanks where the water would be channeled for storage. This can then be used for all sorts of non-potable water needs in the house such as flush toilets or feeding washing machines, however to drink it the water would need to be filtered and treated correctly.
For detailed information about how they work and are constructed, please read our project all about rainwater harvesting.
The major advantage here, other than the obvious environmental benefits, is the fact that rain water is FREE and can save you huge amounts on mains water, particularly if you are on a metered supply.
The down side is that it is a specialist job to install a rainwater harvesting system which in turn makes it expensive, prohibitively so if retrofitting on most occasions. They also require an overflow (into the mains drainage system) for when the system is full and cannot cope with more rain.
How Permeable or Porous Driveways are Built
The driveway will need to be dug out and then built back up to the desired surface level. The depth you need to dig out the driveway does depend on the local conditions; if the soil is loose and will not provide a firm base you will need to dig out more to provide a deeper sub-base to ensure stability.
As a rule of thumb, if you can drive a 150mm (6 inches) peg into the ground then it is not strong enough to support your driveway and will need digging out until you hit a firmer, more solid base.
After digging out, a weed mesh or geotextile membrane should be laid to prevent any weeds growing up and through from the soil below, but also to bind the sub-base above it, which stops it sinking into the soil. As such membranes are porous any water will be able to pass through it easily.
Over the weed mesh 150mm (6 inches) or sub-base is laid. For a traditional impermeable driveway the sub-base would have been made from hardcore or scalping’s that contained silt and sand.
This is often referred to as MOT Type 1 sub-base and can be purchased from almost any builders merchant. The problem is that when compacted the sand and silt will stop water passing through it easily even if the drive surface is permeable.
The solution is to use a sub-base that has been “open graded” so that there are none of the finer particles that stop the water flowing through. With only the larger aggregates it must be compacted in the same way but the holes between the particles will remain and allow any water to pass through.
When purchasing usch a sub-base material you will need to ask for 4/20 or Type 3 sub-base.
With the sub-base in place and compacted correctly the driveway surface can be laid. This will be in the region of 200-250mm (8-10 inches). This makes the total depth you have to dig out to be approximately 350-400mm (14-16 inches).
The type of driveway you are laying will dictate how it is done. We explain more in the projects listed below about the different options:
Constructing a permeable driveway is a project that requires a greater understanding than if simply constructing an impermeable one, so it is wise to use a qualified contractor. See here for reliable contractors.
If you have a clay type soil which does not readily absorb water then extra work might be required to ensure that the water does not soak through the drive surface and simply sit in a “puddle” in the sub-base. It might be necessary to have a pipe in the sub-base to take excess water to your water drainage system for the rest of the house.
A similar overflow pipe will be required for a rain garden so that it can drain away excess overflow water. Soakaways and rain gardens should not be built near the foundations of your home. Typically they need to be 3 or ideally 5 metres away, but this should be confirmed with your local building control who will know more about the local soil conditions.
Maintenance Consideration for a Permeable Driveway
The precise maintenance required for a driveway will ultimately depend on the type or driveway you have, but there are a few important rules of thumb that you can follow to ensure that it continues to work well.
The key thing to remember is that they work by allowing water to pass through them and soak away into the soil below. For this to happen there needs to be gaps and pores for the water to travel through, so these should not be allowed to become blocked up.
Therefore your maintenance of a permeable driveway should include:
- Clear any leaves or mud that collects on the driveway – this can break down and pass through the surface and block the pores
- Brush away any dirt or dust that collects on the surface or use a pressure washer
- Remove any weeds, rather than using a weed killer as the weed can then rot down and block the pores
- Don’t put any materials, like sand, cement or oils on the surface of the driveway which could reduce the porosity
- Ensure that soil and dirt for the garden are not washed onto the driveway
If you understand how they work it is easy to understand what needs to be done to ensure that you permeable driveway remains permeable and porous and in tip top working condition.
Planning Permission for a Permeable Driveway and other Factors to Consider
Up until 2008 (and 2013 in Wales, similar rules apply in Scotland too), creating a driveway in your front garden was considered “permitted development”. However to reduce the amount of water entering the drainage systems, which were becoming overwhelmed leading to flooding, these rights have been taken away – except if a permeable driveway is being created.
If your driveway or paved area is impermeable and greater than 5 meters square, you will need to get planning permission for a new or replacement. If the driveway is permeable or the water is directed to a boarder or lawn to drain way it will be considered a permitted development.
For more information about the construction of a driveway in your front garden or front of your property, see the Planning Portal.
Other Areas Around Your House
There are no restrictions for patios and paving, like a driveway, that is not part of your front garden, however you might need planning permission if there are significant works. For more information see the Planning Portal.
Getting to your front garden might involve driving across the foot path or pavement from the street. You will need to apply to the council for permission to do this. This is required so that they can check that there are no utilities (water pipes, TV cables, etc.) which could be damaged or disrupted by your plans.
There are a few other things that will affect what you can do and the suitability of a permeable driveway. Here are some of the most common, but for a very detailed look at all planning factors involved see the guidance from the Precast Concrete Paving and Kerb Association.
- Slope – the drive should slope away from the house, but if it doesn’t you will need a drainage channel to collect any excess water before it gets to the house. Slopes in excess of 1:20 are unlikely to be suitable for permeable driveways, so you will have to use a soakaway or other solution. You should not direct water on to a neighbour’s property
- Services – As we have mentioned you need to check with the council about dropping the curb so that there are no issues caused with any utilities. The same will apply to your own drive. Check there are no pipes or cables running underneath where you want to put the drive. If there are, you will have to arrange to have them moved by the relevant utility company, but this can cost!
- Contaminated sites – If the site has been contaminated by previous use then there might be a restriction on allowing water to soak into the ground. If this is the case you should seek specialist advice
- Access – We have already discussed the drop curb but you should also consider whether you are going to inconvenience neighbours or have suitable access yourself
The reason for building a permeable driveway, rather than a traditional impermeable one, is to reduce the amount of excess water runoff that can overwhelming drainage systems. This is encouraged by the planning regulations. Hopefully you will see that there are good reasons for going down this route and now understand all the options for the different types of permeable driveways and porous hard surfaces.