Ballast systems — roofs and podiums

System Description

Washed river pebble is the most widely used ballast material for loose-laid single-ply membrane roof systems in Australia. The rounded, smooth particle shape is critical — it distributes load across the membrane surface without point concentrations that sharp crushed aggregate would create. Washed pebble is free of fine particles and dust that could block drainage or contaminate the membrane surface. BCSands (Sydney) specifically markets 40–75mm rounded river pebble for rooftop ballast applications, describing its large size as preventing displacement by birds or wind. This is consistent with the international single-ply membrane industry standard that recommends larger particle sizes (20–40mm or larger) for roof ballast over smaller gravel that can be displaced by wind action. Minimum 50mm depth and minimum 80 kg/m² in the field zone per the Sika Sarnafil and Sikaplan gravel ballast specification — perimeter and corner zones require heavier ballast per the wind uplift analysis for the specific project. Wolfin (Projex Group) and Fatra Australia (Fatrafol) systems use equivalent or greater weights determined by the project-specific wind uplift analysis. A protection board or separation layer must be placed between the membrane surface and the pebble ballast on most membrane systems — confirm with the membrane manufacturer whether a protection layer is required before placing pebble directly on the cured membrane.

System Description

Precast concrete pavers are used as ballast on loose-laid single-ply membrane roof decks and podium slabs where a flat, walkable surface finish is required rather than loose pebble. The paver dead weight holds the membrane against wind uplift while providing a maintenance-accessible surface above the membrane. Standard precast concrete pavers for roof ballast applications are typically 400×400mm or 600×600mm in plan, 40mm thick, weighing approximately 15–17 kg each — providing approximately 95–110 kg/m² when placed edge-to-edge without gaps. Fatra Australia's Fatrafol ballasted system specifically lists adjustable chairs/pedestals and pavers as the ballast system for the Fatrafol 810v PVC membrane. Wolfin (Projex Group) loose-laid systems are commonly ballasted with concrete pavers on podium deck applications where the finish and access requirements favour a flat paved surface over loose pebble. Pavers used as ballast must be placed on a protection board or separation layer above the membrane — not directly on the membrane surface. The paver edges and corners can concentrate load on the membrane surface and damage the membrane face without a protection layer between them. Where pavers are placed on pedestals, the pedestal system provides the ballast dead weight — confirm the pedestal and paver combination provides sufficient weight per m² against the wind uplift design.

System Description

Fatra Australia offers a complete ballasted roof waterproofing system using the Fatrafol 810v reinforced PVC membrane — confirmed on the Fatra Australia website for concrete uninsulated ballasted roof and podium applications. The Fatrafol 810v is loose-laid on the concrete substrate with adjacent rolls hot-air welded at seams. Ballast is then placed above the membrane to hold it against wind uplift. Fatra specifies that ballast can be pebbles, adjustable chair/pedestal and paver systems, or floating deck systems — providing flexibility to suit the project finish and access requirements. The insulated variant of the Fatra ballasted system places XPS insulation above the membrane (inverted roof configuration) with pebble or paver ballast above the insulation — see the Tapered Insulation page for the Fatra insulated system specification. All Fatra systems are installed by Fatra Australia-accredited applicators. The ballast type and minimum weight are confirmed by the wind uplift analysis for the specific project. Fatra Australia provides CAD details, WORD specification templates, technical data sheets, and certification documentation for the ballasted system — available through fatraaustralia.com.au.

System Description

Wolfin IB is the standard Projex Group loose-laid ballasted single-ply PVC membrane for roof decks, podium slabs, large terraces, and green roofs. The polyester-reinforced PVC membrane is unrolled loose-laid over the prepared substrate — no bonding or mechanical fixing to the substrate is used in the field. Adjacent rolls are overlapped and hot-air welded to create continuous watertight seams. The Wolfinsteel galvanised or 316L stainless steel perimeter profiles are used to terminate and fix the membrane at all edges, upstands, and perimeters — the fixings are encapsulated within the Wolfinsteel profile body and the membrane is welded to the profile face, eliminating exposed mechanical fixings through the membrane. Pebble or concrete paver ballast is placed above the membrane to provide wind uplift resistance in the field area of the roof — the Wolfinsteel profiles provide mechanical restraint at the perimeter where wind uplift forces are highest. The combination of perimeter mechanical fixings (Wolfinsteel) and field ballast is the standard Wolfin loose-laid design — it avoids the need for heavy ballast at the perimeter zones by using mechanical restraint at those locations. All Wolfin installations are by Projex Group-accredited applicators, inspected and signed off by Projex Group, with a single-point warranty on workmanship and materials for up to 15 years issued to the building owner.