Excavation-Basis Void Comparator

A 95% void ratio describes a bare module. A stone-embedded chamber’s headline number describes something else again. Compare both on the only basis a contractor pays for: storage recovered per cubic metre excavated.

StormGrid module

Module layers

Cover over the tank (mm)

Bedding below the tank (mm)

Compare against

Same basis, both systems

Storage per m² of tank	0.950 m³
Excavation per m² of tank	1.750 m³
StormGrid, excavation basis	54.3%
Chamber system, as published	54.5%
Storage-zone depth (modules only)	1.00 m

On an excavation basis the two land in much the same place. The crate’s real advantage is a shallower storage zone, because none of it is stone.

Where the 40% figure comes from. The “95% vs 40%” comparison sets a bare plastic module against the porosity of crushed stone. Drainage aggregate is required to hold a minimum of only 30% void under a 300 psf compressive load (US patent 6,467,996 B1), and geocellular modules are recorded at up to 96% (susdrain). Neither number is an installed system void.

Get a like-for-like comparison for your depth constraint