Ballasted roof
A ballasted roof is a flat-roof membrane laid loose and held against wind uplift by gravel or pavers on top, leaving the membrane accessible for inspection.
Ask Chalkline about this →A ballasted roof is a flat-roof membrane laid loose and held down against wind uplift by a ballast layer of gravel or pavers on top, rather than being adhered or mechanically fastened. The ballast weight resists the wind, and the membrane stays accessible for inspection.
In a ballasted system the membrane sits loose on the substrate (or over insulation, in an inverted roof) and a layer of round river gravel, or concrete pavers on pedestals, is placed over it. The dead weight is what stops the membrane lifting in wind, so the ballast has to be sized to the wind region and is generally limited to low-rise, low-exposure roofs where the required weight is achievable and the structure can carry it.
The advantages: the membrane is not penetrated by fasteners, it is protected from UV and foot traffic by the ballast, and (with pavers on pedestals) it stays accessible for inspection and repair. The disadvantages: significant dead load on the structure, ballast can be scoured or displaced in extreme wind, the gravel can block outlets, and finding a leak under ballast is laborious.
For a builder the practical points are that a ballasted roof is a structural decision first, the slab or framing must carry the ballast dead load, so it has to be designed in, not added later. Keep ballast clear of outlets and provide an overflow, size and place the ballast to the wind design (especially at perimeters and corners), and on an inverted/protected-membrane roof make sure the insulation under the membrane is rated for that wet, loaded position.
Also known as: Loose-laid roof, ballasted membrane, inverted roof (protected membrane).
Category: Roofing / Membranes.
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References
- Roofing membranes (Chalkline) (verified 2026-06-01)
Last updated: 2026-06-01. Verified: 2026-06-01. Quarterly review for currency.