Stand at the bottom of your driveway during a heavy summer storm and watch where the water goes. On a standard slab, it gathers speed down the slope, spreads across the low end, and heads for the garage door, the footpath or the neighbour’s fence. Something has to stop it.
The two most common fixes work in opposite ways. Permeable concrete stops run-off at the source, by letting rain soak through the driveway itself. A drainage pit, or a grated strip drain, lets the water run off as normal, then catches it at a low point and pipes it to the stormwater system. Neither is better in every case. Permeable concrete suits flat to gentle sites where you also want to reduce run-off overall. A drainage pit suits steep sites, heavy clay, and existing driveways. On many properties, the best result comes from using both.
How each one works
Permeable concrete. Rain passes straight through the surface into a stone base below. From there it soaks into the soil, or drains slowly through an underdrain. Very little water runs off the surface at all.
Drainage pit or strip drain. The driveway sheds water as usual. A grated pit, or a long channel drain across the driveway, collects it and sends it through pipes to the legal point of discharge, usually the street drain or a council stormwater connection.
Side-by-side comparison
| Factor | Permeable concrete | Drainage pit or strip drain |
| Reduces total run-off | Yes, water soaks in on site | No, water is moved elsewhere |
| Counts towards permeable site area | Can, if accepted by the surveyor | No |
| Upfront cost | Higher, because of the deeper base | Lower for most driveways |
| Steep slopes | Limited to gentle grades | Works on any slope |
| Heavy clay soils | Needs an underdrain | Works well |
| Retrofit to an existing driveway | Means replacing the driveway | A drain can be cut in |
| Maintenance | Sweeping and yearly cleaning | Clearing grates and the pit |
| How it fails | Gradually ponds as pores clog | Overflows at one point if blocked |
Run-off and permeability often come up together on new builds. If you need to check whether your site needs more permeable area, note that a drainage pit will not help with that requirement, while a permeable surface may.
When permeable concrete is the better choice
- New driveways on flat or gently sloping blocks, where you are pouring a fresh slab anyway.
- Sites needing more permeable area to meet building or planning requirements.
- Planning permits with stormwater conditions that favour reducing run-off at the source.
- Large paved areas, where piping all the run-off would mean big pits and pipes.
- No easy stormwater connection, where getting water to a legal point of discharge is difficult or expensive.
Permeable concrete costs more to install than a standard slab. Weigh up the cost difference between permeable and standard slabs against any drainage work it saves.
When a drainage pit is the better choice
- Existing driveways. Cutting in a strip drain is far cheaper than replacing the whole surface.
- Steep driveways, where water moves too fast to soak in and permeable concrete is harder to build. See our tips on managing water on sloping driveways.
- Heavy clay soils, where water soaks in slowly and a permeable system would need its own underdrain.
- Areas next to house footings on reactive clay, where you want water piped away rather than soaking into the ground.
- Tight budgets, where standard driveway concrete with a well-placed drain does the job.
Using both together
Combining the two often gives the most reliable result:
- A permeable driveway with an overflow drain at the low end. The surface handles everyday rain, and the drain catches anything left over in a severe storm or as the surface ages.
- An underdrain inside the stone base, connected to stormwater. This is common on clay soils, and it lets a permeable system work where soakage alone would be too slow. We explain underdrains for clay soils in our base layers article.
- A hybrid layout. Standard concrete with a strip drain on the steep section, and permeable concrete on the flatter parking area.
Maintenance compared
Both systems fail if they are ignored. A drainage pit needs its grate and sump cleared of leaves and silt, particularly in autumn, or it overflows at one spot. A permeable surface needs regular sweeping and a yearly clean, or it slowly loses its drainage across the whole area. For permeable surfaces, check the surface cleaning frequency that suits sites with trees and garden beds.
Frequently asked questions
Is permeable concrete cheaper than installing a drainage pit?
Usually not for a single driveway. A drainage pit or strip drain generally costs less, although permeable concrete can save money where a stormwater connection would be long or difficult.
Can I add a drain to my existing concrete driveway?
Yes. A strip drain can be cut across an existing slab and connected to stormwater, which is often the simplest fix for water heading towards a garage.
Does a drainage pit count towards permeable site area?
No. Pits move water elsewhere, so the paved area still counts as impervious.
