Drainage under pavement - how does that work?

For paving, the substructure is critical to the quality and durability of the paved area. Again and again, the question arises whether a drainage under plaster is necessary and useful, and how to properly apply it.

Need for drainage

Basically, drainage is only necessary if the infiltration capacity of the soil is too low to absorb seeping surface water quickly. In this case, pourable paving stones are no longer helpful - the water seeps into the substructure, but it can not seep further away into the soil fast enough and accumulates.

To test soil seepage

Less infiltratable soils are usually very loamy or peaty soils. This soil condition is also called "cohesive" or "heavy soils". How well a soil is able to infiltrate is easy to test for yourself.

1. dig hole in the ground with the dimensions 50 cm x 50 cm x 50 cm (width x length x depth)
2. Fill the hole repeatedly with water for 2 hours.
3. Set a 30 cm mark for the water level.
4. From then on, replenish the seeped water every 10 minutes. Measure the amount of water necessary to reach the 30 cm mark each time. Repeat the whole thing 4 times.

In the table you can see the result according to the amount of water you had to refill:

amount of waterinfiltration capacity
less than 1.5 litersvery low
1.5 liters - 3 litersmediocre
over 3 litersgood infiltration capacity

Alternative to drainage

Before you start to drain the substructure, it makes sense to dewater the pavement itself. Further details can be found in the article "Draining the driveway". By installing drainage channels, you drain the pavement surface directly - and not the substructure.

You do not have to worry about using water-permeable paving stones and can also lay the paving stones as a sealed plaster. If you are not sure whether you should also lay drainage pipes in the substructure beneath your infiltration patches, consult with experts after an on-site assessment.

Tips & Tricks

Note that for sealed paved areas (which are impermeable to water) you have to pay additional sewage fees. These fees vary depending on the municipality. Of course, all drainage systems that are not connected to the public sewage system are excluded (in some cases self-drainage is also mandatory!

Video Board: How Permeable Pavements Work