Tree Protection Zones (TPZs)

A driveway can run straight through the Tree Protection Zone of an established tree. Sealed concrete across that ground wasn't an option. Permcon goes down through that section, alongside exposed aggregate concrete on the rest of the drive.

Why a TPZ changes how a driveway is built

A Tree Protection Zone exists to keep the ground over a tree's roots breathing. Compact that ground, or seal it, and the roots lose water and air. The tree doesn't die in week one. It declines slowly, over years, after the driveway goes in. Councils and arborists ask for a permeable surface for exactly this reason, and the same condition applies wherever a driveway, path or hardstand crosses protected ground.

Permcon lets air and water keep reaching the roots through the pavement itself. Rain passes through the slab into a base of clean screenings, then continues down into the root zone instead of shedding off to the kerb. The voids in the slab let the soil beneath it breathe. At 25+ MPa, the slab still carries the cars every day, so the surface meets the TPZ and council permeability conditions on the permit rather than working around them.

Matching two surfaces on one driveway

The harder part of this job wasn't the engineering. It was getting the aggregate size and colour in the Permcon to line up with the exposed aggregate finish. Get the colour or the stone size wrong and the mismatch shows from the street, right where the two surfaces meet. That's the balance on a residential TPZ job: meet the arborist's conditions without the driveway looking like it was built to two different briefs.

The same idea under a bus stop

The same approach scales up. We poured a bus stop on a VicRoads road at Mornington inside a Tree Protection Zone: 175 mm of Permcon over a 100 mm aggregate sub-base, 275 mm in total. It carries buses every day while the roots underneath keep getting water and air. Thickness is the lever, not the mix. The slab gets deeper as the load gets heavier; the mix under a driveway and under a bus stop is the same.

Anyone planning a driveway in a tree protection zone should sort the paving approach out early, before an arborist report or a council condition forces a redesign halfway through. See how the system works under trees on our tree protection zone paving page. We've put photos of this week's driveway up on LinkedIn, the two surfaces side by side.