Repair Systems — Protection & Overburden
Ballast systems — roofs and podiums
Technical product reference for ballast systems used on loose-laid single-ply waterproofing membrane systems on roof decks and podium slabs in Australian Class 2 strata apartment buildings.
What are ballast systems?
Ballast is the weight laid over the membrane on a protected / inverted roof or podium to hold down the insulation and membrane and resist wind uplift. It ranges from loose rounded stone and gravel, through concrete ballast pavers, to pavers mounted on adjustable pedestals that give a level, trafficable deck. Ballast is not waterproofing — it protects and restrains the membrane — and rounded, washed stone (not sharp crushed aggregate) should be used over a protection / separation layer so the membrane is not punctured. Selection turns on the ballast weight against wind uplift, the structural dead-load capacity, and the protection layer beneath.
Product Reference
Individual products — one card each — scroll to view all
Generic / supplier
Rounded River Pebble / Smooth Stone
Rounded washed stone ballast (loose-laid)
Rounded washed river pebble / smooth stone is loose-laid ballast (typically around 20–40 mm graded) that holds down insulation and membrane on protected and inverted roofs. Rounded stone avoids the sharp edges that can damage a membrane. Confirm grading, ballast weight against wind uplift and the structural load with the engineer.
Generic / supplier
Gravel Ballast (Drainage Aggregate)
Graded gravel ballast / drainage aggregate
Graded washed gravel is loose-laid ballast that can also act as a drainage / blinding layer in podium and roof build-ups. It should be laid over a protection or filter layer and not placed directly on the membrane. Confirm grading, ballast weight against wind uplift and the structural load with the engineer.
Generic / supplier
Concrete Ballast / Paver-on-Pedestal
Concrete pavers as ballast over a protected membrane
Concrete pavers — often on adjustable pedestals — are used as ballast that doubles as a level, trafficable surface on protected / inverted roofs and podiums, with a drainage void beneath the pavers. Confirm the paver dead load, pedestal layout and the membrane protection layer with the engineer.
Elmich
Elmich VersiJack Pedestal (with paver ballast)
Adjustable pedestal system supporting paver ballast
Elmich VersiJack is an adjustable pedestal system that supports concrete or stone paver ballast level over the membrane, leaving a free-draining void beneath and allowing a level deck over a sloping slab. Confirm the pedestal height range, paver load and membrane protection at the pedestal bases with Elmich.
Generic / supplier
Ballast Protection Layer (Geotextile / Slip Sheet)
Protection / separation layer beneath stone or paver ballast
A ballast protection / separation layer (heavy non-woven geotextile or protection mat) is laid between stone or paver ballast and the membrane to protect it from point loads and abrasion on protected / inverted roofs and podiums. Confirm the protection layer to suit the ballast and the membrane manufacturer's requirement.
System Comparison
Ballast systems — confirm all selections against the current manufacturer TDS before specifying.
Scroll the table sideways to see every column →
WIND UPLIFT ANALYSIS IS MANDATORY BEFORE BALLAST WEIGHTS ARE SPECIFIED — DO NOT ASSUME A STANDARD WEIGHT IS SUFFICIENT FOR ALL ZONES
The required ballast weight per square metre varies significantly across the roof area — perimeter zones and corner zones are subject to wind uplift forces two to three times greater than the central field area. Applying uniform ballast across the full roof without increasing the weight at perimeter and corner zones is one of the most common and dangerous errors in ballasted single-ply roof specification. A wind uplift analysis based on AS/NZS 1170.2 wind loading — accounting for building height, roof geometry, location, and wind region — is mandatory before ballast weights are determined. This analysis must be performed by the structural engineer or confirmed with the accredited membrane applicator who is responsible for the system warranty. Do not proceed with ballast specification on the basis of a standard depth or weight alone.
STRUCTURAL ENGINEER MUST CONFIRM THE ROOF OR PODIUM SLAB CAN CARRY THE BALLAST DEAD LOAD BEFORE SPECIFICATION
Ballast imposes a significant additional dead load on the roof or podium slab — 80 kg/m² of pebble ballast adds approximately 0.8 kPa of dead load, and 100mm of pebble ballast adds approximately 1.5–1.7 kPa. On existing Class 2 strata roofs and podium slabs, the original structural design may not have included provision for ballast loads — many existing slabs were designed for membrane, screed, and tile loads only, not for an additional 80–110 kg/m² of ballast material. The structural engineer must confirm the slab's dead load capacity before ballast is specified. If the slab cannot carry the ballast load, a mechanically fixed or fully bonded membrane system must be specified instead of a loose-laid ballasted system.
SHARP CRUSHED AGGREGATE MUST NOT BE USED AS ROOF BALLAST — ROUNDED SMOOTH PEBBLE ONLY
Crushed rock aggregate has sharp, angular edges that concentrate load at point contacts with the membrane surface — under the weight of the ballast above, these point loads can puncture, abrade, and damage the membrane over time. Only rounded, smooth, washed river pebble or similar naturally rounded stone must be used as roof ballast. Crushed blue metal, crushed limestone, and similar sharp aggregate products must never be specified as membrane ballast regardless of their particle size. Confirm that the ballast material supplied is rounded and washed before acceptance on site — reject any ballast delivery that contains sharp-edged crushed material.
ALL MEMBRANE SEAMS MUST BE TESTED AND CONFIRMED BEFORE BALLAST IS PLACED — SEAMS CANNOT BE ACCESSED AFTER BALLASTING
Once ballast is placed over the membrane, the membrane surface and all seams are permanently inaccessible without removing the full ballast load — a significant cost and disruption on an occupied strata building. All hot-air welded seams on the loose-laid single-ply membrane must be tested for continuity using point probe or air lance methods, inspected and confirmed defect-free, before any ballast is placed above. Any seam that fails testing must be repaired and re-tested before ballasting commences. The membrane manufacturer's accredited applicator is responsible for seam testing and must document the results as part of the project quality record before the installation is covered.
Disclaimer
This page provides general technical information only. Final ballast specification must be confirmed against the membrane manufacturer's system requirements, a wind uplift analysis per AS/NZS 1170.2, structural engineer confirmation of slab dead load capacity, NCC requirements, and accredited membrane applicator advice. Ballast weights specified on this page are indicative minimums for field zones only — perimeter and corner zones require heavier ballast confirmed by wind uplift analysis. Sharp crushed aggregate must not be used as membrane ballast. All membrane seams must be tested before ballast is placed. Do not rely on this reference as a substitute for professional structural engineer, wind engineer, or waterproofing consultant advice.