Does open graded base go under Vancouver permeable pavers?

Yes — open-graded aggregate base is essential under permeable pavers in Metro Vancouver. It's not just recommended; it's the core engineering component that makes the entire permeable paving system function. Without it, rainwater has nowhere to go and the system performs no differently than conventional paving.

How the Open-Graded Base System Works

Permeable interlocking concrete pavement (PICP) relies on a layered aggregate system that allows water to infiltrate downward through the pavers, through the joints, and into a reservoir of clean, angular stone beneath. Unlike a conventional interlock base — which uses well-graded crushed gravel (containing fines that compact tightly and shed water) — the open-graded base uses aggregate with the fines removed. This creates a network of void spaces between the stones that stores water temporarily and releases it gradually into the subgrade soil below.

A properly engineered PICP base in Metro Vancouver typically consists of three distinct layers. The bottom layer is ASTM No. 2 or No. 57 open-graded stone (approximately 19-37mm clean crushed rock with no fines), typically 250-450mm deep depending on the stormwater storage volume required. Above that sits a choker course of ASTM No. 57 or No. 8 stone (9-12mm clean crushed rock), typically 50-100mm deep, which provides a transition layer that prevents the larger base stone from migrating upward into the bedding layer. The top layer is the bedding course of ASTM No. 8 or No. 9 stone (2-6mm clean chips), typically 25-50mm deep, which replaces the traditional bedding sand used in conventional interlock. The paver joints are also filled with the same small clean aggregate rather than polymeric sand, keeping the infiltration pathway open all the way to the surface.

Why This Matters Especially in Metro Vancouver

Metro Vancouver receives over 1,200mm of annual rainfall — and North Shore communities exceed 2,000mm — with the majority falling between October and March. The City of Vancouver, Surrey, and other municipalities are actively encouraging permeable paving as part of green infrastructure and stormwater management initiatives, and some offer reduced stormwater utility fees for properties that reduce impervious surface area. The open-graded base is what makes permeable pavers qualify for these benefits — it must be designed to infiltrate a specified volume of rainfall per hour to meet municipal stormwater performance targets.

Richmond and Delta present a specific challenge: the water table in these areas is high, and the subgrade soil has limited capacity to absorb additional infiltration. In these locations, the open-graded base functions more as a detention reservoir (holding water temporarily) than a true infiltration system, and an overflow outlet pipe connected to the storm drain is typically required. A qualified contractor familiar with Lower Mainland soil and drainage conditions will design the base depth and outlet configuration accordingly.

What Not to Use

Never substitute conventional well-graded crushed gravel (road crush, 3/4-inch minus) for the open-graded aggregate in a PICP base. Road crush contains fines that fill the void spaces, eliminate drainage capacity, and turn your permeable paver system into a conventional impermeable surface within a few years as the fines migrate and compact. Similarly, never use polymeric sand in the joints of permeable pavers — it seals the joint and blocks infiltration entirely.

Geotextile fabric placement also differs from conventional interlock. In a PICP system, filter fabric is placed on the sides of the excavation (against the native soil walls) but not on the bottom — you want water to infiltrate into the subgrade, not be blocked by fabric. This is the opposite of what some contractors accustomed to conventional interlock installation might instinctively do.

Permeable paver installation is not a DIY project. The aggregate specifications, base depth calculations, drainage outlet design, and geotextile placement all require professional knowledge and ideally ICPI PICP certification. An improperly built permeable base either fails to drain (defeating the purpose) or drains too aggressively without proper overflow management (causing erosion or neighbour drainage issues).

If you're planning a permeable paver project in Metro Vancouver, Vancouver Interlock can match you with experienced local contractors familiar with Lower Mainland soil conditions, municipal stormwater requirements, and PICP installation standards — at no cost to you.