Permeable Paving: The Options, and Where Poured Fits

Five surfaces, one job: get the rain into the ground

A footpath that sheds every drop of rain to the kerb is doing the opposite of what a council now wants from a paved site. Permeable paving is the fix: any hard surface built so water soaks through it into the ground below, instead of running off to a stormwater pit. Every kind gets the water in the same way underneath: through the surface itself, or through gaps between units, dropping into a bed of clean stone. That stone holds it until the soil takes it, or a pipe lets it go at a steady rate. The difference between the five kinds is where the water gets in, and what the surface does underfoot or under a wheel.

Loose gravel

Loose gravel is the cheapest permeable surface going, and it drains without any help because nothing binds the stone together. Leave it a season and stone starts to travel: ruts form in the wheel tracks, and a pram, a wheelchair or a wheelie bin has a rough run across it.

Resin-bound gravel

Bind that same small stone with a clear resin over a prepared base and you get a smooth, porous layer instead, at home on a courtyard, a garden path or around a pool.

Grid and grass cells

Plastic or concrete cells filled with gravel, or with soil and turf, cost little to install and look, when turfed, close to lawn. They suit overflow parking at a showground or a fire truck's access lane. Daily traffic on the same two tracks kills the grass there well before the rest of the paddock thins.

Permeable pavers

Solid concrete or clay units, laid with joints wider than a standard path and packed with fine gravel rather than mortar, put the load on the units and the drainage in the joints. That suits a courtyard pattern or a small entry (see our permeable pavers page), but the joints want topping up as the gravel wears out of them.

Poured permeable concrete

Permcon, our permeable concrete guide covers the mix in full, is poured concrete with a void content of 20 to 25 per cent. The result is a matrix of joined-up voids running through the whole slab. Rain gets in across the whole surface rather than concentrating at a joint, in one continuous pour with nothing to lift or spread over time. It's still strong enough to drive on: 25+ MPa, poured at 125 mm thick for most jobs and thicker again for a car park carrying trucks. A crew can lay 500 m² and more in a day, up to 70 per cent faster than traditional permeable paving, because nothing gets set out piece by piece.

Poured concrete suits driveways, car parks, footpaths, sports courts, tree protection zones, anywhere feet or vehicles cross daily and the whole surface, not just the gaps in it, has to keep draining. Units still make the better call in a few spots though: a heritage paving pattern, or a strip that has to be lifted again for a service trench. Our permeable concrete vs pavers comparison runs through when each wins.

The base, and where the water goes next

Every 100 mm of clean screenings in the base stores around 28 litres per square metre. On clay, or anywhere the ground drinks slower than a storm arrives, a slotted under-drain at the bottom of that base carries the water away at a controlled rate rather than waiting on the clay to manage it.

All five kinds clog if silt and leaves sit on them long enough. Grass cells need mowing, loose gravel needs raking back into place. A poured slab asks for a monthly look and one sweep a year. Councils count a permeable surface toward a site's permeable area if the design shows where the water actually goes.