How permeable surfaces work

Loose gravel

This is the simplest type of construction. The driveway sub-base is covered by a surface layer of gravel or shingle.

Gravel with different shapes and colours is available to make the surface more decorative.

A strip of block paving or asphalt at the entrance can limit the loss and spread of gravel from the drive.

Hard permeable and porous surfaces

Hard surfacing which allows water to soak into it can be built with porous asphalt, porous concrete blocks, concrete or clay block permeable paving.

The material has open voids across the surface of the material or around the edges of blocks that allow water to soak through

To work effectively permeable surfaces should be laid over a sub-base which differs from traditional hardcore which has a lot of fine material in it (sand and silt) that stops water passing through it easily.

For permeable and porous driveways different sub-base materials are required that allow water to pass through and also store the water for a while if it cannot soak into the ground as fast as the rain falls.

Various materials are available and two examples are known as 4/20 and Type 3 sub-base.

Materials for permeable sub-base are described as open graded and consist only of larger pieces of stone that have spaces between to store water.

Read more about important issues to consider and more detailed practical advice in 'Guidance on the permeable surfacing of front gardens'.