Permeable Paving in Cape Town: How It Works and When It’s Worth It

Permeable paving lets rain soak down between the blocks of a driveway instead of running off it into the road. Whether it is worth it on your property comes down to how your ground drains and, if your project needs City approval, what that approval asks for.

Where we stand: we lay driveway paving in Cape Town, and we will price a permeable build-up next to a standard one if you ask. The technical detail below comes from the Concrete Manufacturers Association (CMA), the body for precast concrete paving producers, which champions permeable block paving. We quote it and say where the view is ours.

How permeable paving works

Rain runs between the blocks, through joints filled with small angular stone, into a sub-base that holds it and releases it slowly: into the ground or onward to a drainage system [3].

• The surface: blocks with “enlarged joints or holes in the corners of the pavers”, filled with a material specific to each product, “which is an angular aggregate, not sand” [3].
• The layer below: a permeable sub-base that the CMA says is “specifically designed to accommodate water”, where it is stored and released slowly [3].
• The edges: like any concrete block paving, “all cbp must have an edge restraint”, which may be cast in situ, precast or an existing structure [2].

The CMA describes three systems, which look the same on the surface [3]:

• System A, full infiltration: for ground that drains well. All the water soaks into the ground; none goes to conventional drains.
• System B, partial infiltration: some soaks in, and outlet pipes carry the excess to other drainage.
• System C, no infiltration: for ground that drains poorly or contains pollutants. A membrane turns the sub-base into a storage tank, emptied by outlet pipes.

Ordinary block paving sheds rain off the surface instead, and the CMA says its joints “eventually become clogged with road detritus and impermeable to water” [2].

What Cape Town’s stormwater rules actually say

The 2005 Stormwater Management By-law does not mention paving [1]. The City’s 2009 stormwater policy can require stormwater measures on private developments, a single erf included, but it does not name permeable paving [4].

The 2005 by-law [1]:

• We searched its text for paving, permeable, impervious and attenuation. None of those words appears.
• Section 8 puts private drainage on the owner, who must “at own cost, keep such stormwater systems functioning effectively” [1].

The 2009 Management of Urban Stormwater Impacts Policy [4]:

• Its definition of development includes “paving”. New developments, including “additional development on an already developed site”, shall be designed to incorporate sustainable urban drainage systems [4].
• Council “may require” those measures inside a private development, and the policy names “private single erf developments” [4].
• Its interim criteria are lighter for small existing sites outside sensitive catchments. Under 4,000 m², with more than 600 m² of hard surface, on-site treatment and runoff control are “not required but encouraged where practicable”, with regional measures doing the work instead [4].
• The City’s 2022 roads and stormwater standards add that this holds only where those regional measures are available; if they are not, on-site treatment and attenuation “will typically be required” [6]. Neither document sets a criterion for a site under 4,000 m² with 600 m² or less of hard surface.
• Stricter targets apply to greenfield sites and to sites in the catchments of what the City deems sensitive waters [4].

We read the policy as approved on 27 May 2009, and the City’s 2022 standards, which still cite it [6]; the policy says its criteria can be revised without re-adopting it [4], so check the current position with whoever draws your plans. Where a stormwater design is required, permeable paving is one option, and the CMA says it can also take runoff from roofs and nearby hard surfaces [3].

What drives the price

We don’t publish a rate for permeable paving. The part a site visit settles is the build-up under the blocks, which follows from how your ground drains [3].

• The site test. The permeability of the ground, “established from tests on site”, is one of the key criteria for choosing a system [3].
• Which system you need. System A needs no pipes or gulleys. System B adds outlet pipes, and System C adds an impermeable membrane as well [3].
• The other factors the CMA lists: groundwater level, pollution prevention, discharge consents and how close the paving is to buildings [3].
• What it replaces. The CMA calls full infiltration “a particularly economic solution” because it removes pipes and gulleys [3]. In our view, compare the whole drainage cost, not just the paving line.

We price it like every kind of paving Paving Cape Town lays, after seeing the site. Ask for both priced side by side, and see how a paving quote is built up.

Where it works and where it doesn’t

It suits ground that lets water soak in. Poorly draining ground, a high water table or paving near the house need weighing up in the design [3], and so, in our view, does a slope.

On the Cape Flats, a 2022 study of the area’s sands measured surface infiltration rates that “will result in generally minor runoff or ponding”, though the same study notes that fines and detritus on the surface, or less permeable layers below, can still cause ponding and flooding in heavy rain [5]. It also put average winter groundwater about 2 m below ground, “with the water table rising above ground level in places”, and found the sands “highly variable” [5]. In our view that makes a site test more important there, not less.

Maintenance: what the joints need

Keep leaves and grit off it, and watch for water sitting where it used to drain away. The CMA says the infiltration rate drops as detritus builds up in the jointing material, then stabilises [3].

• How much work: the CMA calls recommended maintenance “minimal”, no more extensive than for conventional block paving [3]. That is the industry body promoting the product.
• What slows it down: “the build-up of detritus in the jointing material” [3].
• How you spot trouble: the CMA says problems “become apparent on the surface with a visual inspection” [3]. In our view, water standing where it used to drain is the sign to get it looked at.
• Topping up: the joint fill is an aggregate specific to each product, “not sand” [3], so ask for that product’s filling.

In our view, sweeping leaves and grit off through leaf-fall is the routine; we don’t publish an interval. Standard paving is different: see the upkeep ordinary block paving needs.

So which suits your driveway?

Our view, as a paving business: let a site test and your plans decide. Go permeable where the ground takes water or a design calls for it, and lay standard paving with proper falls where neither applies.

For a complex or office park, we lay permeable paving on commercial sites to your engineer’s design; see what body corporates should put in a paving spec.

Common Questions

Weighing up permeable against standard paving? We do free on-site assessments across the Peninsula and follow with a written quote, with no obligation to use us for the work. See how a written quote comes together, or call 021 825 6396, weekdays 8am to 5pm.