What Counts as a Permeable Driveway Surface?

Many people are aware that the regulations in England for paving over front gardens for driveways have changed to persuade people to put in permeable driveway surfaces. The other countries in the UK have separate arrangements but are likely to follow suit if they haven't already.

Increased Risk of Flooding

The regulations are largely to prevent water run-off overpowering drainage systems which exacerbates flooding, although there are other reasons. The details of the new regulations and the reasons behind them are covered in more detail in our article New Regulations for Paving Front Gardens

But what options are there for house owners who want to convert their garden into a driveway? In urban areas off-street parking is at a premium and a driveway will add value to a house where parking is scarce in a way that no garden ever would.

What Isn't a Permeable Surface?

It might be easier to start with what isn't considered a permeable driveway surface, although it must be pointed out that the regulations don't actually define permeable and non-permeable surfaces. Those surfaces that we can be reasonably certain are not permeable are concrete, tarmac and almost every sort of block or flag paving.

Having said that, larger stone or concrete blocks can be used for a permeable driveway surface but only if they are laid with an absorbent substrate and large gaps between the flags or blocks. Those gaps need to be filled with gravel or sand to allow water to flow down into the soil below. However, it is difficult and expensive to make a driveway that is stable so it's best avoided in domestic situation, particularly if you are laying the driveway yourself.

Gravel – Perhaps the Easiest Option

It's better to go with a driveway surface that is permeable from the outset. Gravel is a good choice although there is a bit of a conflict when it comes to the laying of the foundations. The advice when making a foundation for a gravel drive is usually to have the foundation higher in the centre and sloping gently away to the sides to speed up drainage.

However, when laying a permeable driveway we are looking to slow down drainage and allow rain to slowly soak through to the substrate below. For this reason it's best to combine gravel with a reinforcing cellular structure. This is pegged down then the gaps are filled with gravel. A secondary advantage of this system is that it holds the gravel in place so it doesn't escape into the surrounding areas.

These cellular systems can be used with materials other than gravel; anything can be used as long as it will allow the water to drain through it. Perhaps the best is soil, as grass and other small plants can be grown, giving back some of the wildlife environment that's been lost by the installation of the driveway.

Permeable Products from Mainstream Suppliers

It's no surprise that the paving industry has responded to the need for good-looking and permeable driveway surfacing products. Many manufacturers now have permeable versions of their block and flag products which usually involve tabs on the blocks to increase the gaps between them to six to eight millimetres.

These gaps can then be filled with loose aggregate and water will drain away into the layers below. It is not enough to lay these products on a traditional foundation though. They need a base of loose aggregate to be put down over a solid substrate or capping layer and then the whole drive effectively becomes a soakaway. Each manufacturer should provide details of this.

Sustainable Urban Drainage Systems

Note that although the new regulations call for permeable paving they do allow for non-permeable driveways to be installed as long as there is adequate provision for drainage within the property. This means that rain water should be dispersed somehow, perhaps into the ground via a soakaway or into tanks for reuse within the property.

You will almost certainly need to go though a planning permission process for this but look into Sustainable Urban Drainage Systems (SUDS) for more information on the technology and techniques involved.