Permeable Concrete Car Parks.

What a permeable concrete car park is

Plain answer first. A permeable concrete car park is a poured concrete pavement with the sand left out of the mix. Cement, water and coarse stone, and nothing filling the gaps between the stones. Those gaps join up into a network of voids, 20 to 26 per cent of the slab by volume, against 3 to 5 per cent in normal concrete. Rain goes down through the bays instead of running across them.

You will see the same material called porous concrete, pervious concrete or no-fines concrete. We pour it wet from the truck in a continuous run, so the car park comes out as poured slabs with cut joints, not thousands of units with sand between them that rut under turning wheels.

What happens when it rains on a carpark that drains

Nothing you would notice, which is the whole point. The slab passes water at roughly 130 to 170 litres per minute per square metre. Even the bottom of that range takes more water than a storm delivers to that square metre. Under the slab sits a base of open-graded stone, and that base holds water in the gaps between the stones until the soil below takes it away, or releases it slowly if the design calls for that.

So there is no sheet of water crossing the aisle, no birdbath sitting in bay 14 for two days, no spray off the tyres and no queue of runoff waiting at one pit in the low corner.

Why a car park is the best place to spend the money

On most commercial and residential developments the car park is the biggest single piece of sealed ground on the site. Seal it and you create runoff you then have to build infrastructure to catch. Make it permeable and the runoff largely stops at the source.

• Stormwater handled where it lands. The stone base doubles as storage, which can shrink or delete pits, pipes and a detention tank from the civil design.
• A WSUD asset, not just paving. Permeable pavement filters sediment out of runoff, detains flow in the base and infiltrates it. That is the behaviour water sensitive urban design policy asks for.
• Room inside an impervious-surface cap. Where a planning scheme limits how much of a site can be sealed, a permeable car park can hand back area, and area is usually yield.
• Trees stay in the islands. Water and air still reach the root zone, which is why permeable concrete is one of the few pavements accepted inside a tree protection zone.
• A cooler car park. Voids and retained moisture mean less stored heat than a dense sealed pavement baking all afternoon.
• No ponding to manage. The open texture gives useful grip, and water does not sit on the surface to form a film in the first place.

Permeable concrete carpark specifications

A car park pavement is normally specified in the 20 to 25 MPa band, which is the strength range that carries cars, utes, vans and light commercial traffic. The void structure passes water at roughly 130 to 170 litres per minute per square metre, so rain drains through the bays rather than sheeting to a pit. With a routine vacuum sweep, a car park slab gives 30+ years of service.

Thickness, base depth and finish are job-dependent, so we will not put numbers on them sight unseen. Tell us the vehicles, the catchment and the soil and we will spec the car park: book a free on-site assessment.

Concrete car park construction for developments and townhouse projects

Most of the car park work we price sits on a site with a yield problem. A townhouse development where the driveway, the visitor bays and the shared paving eat the permeability budget. A childcare or medical centre where the planning scheme caps sealed area. An apartment or unit site where the detention tank has grown large enough to argue with the basement.

Permeable concrete gets used on those jobs for one blunt reason. Area that drains is not treated the same way as area that sheds, so making the car park permeable can change what the scheme is allowed to do.

Where it shifts the numbers

• Impervious-surface caps. A permeable car park can free up sealed area elsewhere in the scheme, which can mean another unit, a wider driveway, or a landscape plan that survives the town planner.
• Detention volume. The stone base is storage. Storage the civil engineer can count means a smaller tank, or on some sites no tank and no pump to maintain for the next forty years.
• Pits and pipes. Fewer grated pits in the bays, less pipework across the site, less trenching around service runs and tree roots.
• Retained trees. Existing canopy on the boundary usually comes with a tree protection zone. A permeable car park is one of the few pavements you can take into that zone at all.

None of that is a promise of approval. Every council words its stormwater and permeability requirements differently, so we work alongside your builder, civil engineer or planner and give them the drainage behaviour in writing, rather than telling you it is a done deal.

Commercial car park concreting, and where we work

Retail and shopping centre parking, office and business park bays, apartment and townhouse car parks, aged care, schools and childcare, council and public car parks, staff and overflow parking, plus the islands and tree pits between them. Our crews pour out of our Mitcham factory in Victoria and work across the country, so car park construction in Melbourne and the wider metro is our home ground, with the same system available interstate.

For the whole-site picture rather than just the parking, see our commercial developments capability.

What car park owners ask before they commit

Concrete carpark or asphalt carpark

Asphalt is cheaper down and quick to lay, and for a plain sealed car park it is a fair choice. It also sheds every drop of rain and gets resealed on a cycle. A permeable concrete carpark costs more as a paving line and does a second job: it is the stormwater system as well as the surface, so the pits, pipes and detention tank that asphalt forces into the civil design get smaller or disappear. Compare whole jobs, not square metre rates.

What does a permeable car park cost

We will not put a rate on this page and then change it when we see your site. Area and access, the soil under the pavement, how much water the base has to store, what has to come out first, the edges and transitions, and the finish are the six things that move the number. Clay versus sand is usually the biggest single swing, because it sets the base depth. The full breakdown, including what to ask any quote you are comparing, is on our permeable concrete cost page.

Can it take a delivery van or a garbage truck

Vans and light commercial vehicles, yes, that is inside the normal design band. A loaded waste truck or a semi-trailer is a different question and we will answer it honestly rather than take the job and hope. Sometimes the answer is a thicker slab and a deeper base on that lane. Sometimes it is a conventional pavement for the truck route and permeable concrete over the bays where the water problem actually is. Tell us the heaviest vehicle at the assessment, not after the pour.

Will it clog with all that traffic

It clogs if it is neglected. Sediment, leaf litter and tyre-carried dust fill the surface voids over time, and in a high-sediment setting an unmaintained car park can lose most of its infiltration capacity within a few years. That is the honest risk, and it is a maintenance line item, not a failure. Vacuum sweeping keeps it clear, pressure washing followed by a vacuum recovers most of what has been lost, and design keeps the problem small: no garden bed draining across the bays, no bare soil upstream, edges restrained. Never let a contractor run a rotary broom over it, because a rotary broom drives the dirt in instead of lifting it out.

Permeable concrete or permeable pavers for a car park

Both drain. The difference shows up under turning wheels. A poured slab is one continuous surface with cut joints, so there are no units to rock or spread where cars pivot into a bay, and no jointing gravel to top up. Pavers have their place, and the full comparison is on our permeable concrete vs pavers page.