Ballasted Roof Systems

Ballasted single-ply systems were installed on Atlanta commercial buildings in the 1980s and early 1990s - loose-laid EPDM or TPO membranes held down by river stone ballast. Most of that inventory is now at end of service life. We assess ballasted systems, perform targeted repairs, and scope transitions to mechanically attached or fully adhered systems when replacement is the right call.

Ballasted roofing - loose-laid single-ply membrane held down by smooth river stone or concrete pavers rather than mechanical fasteners or adhesive - was a popular installation method in the 1980s and early 1990s for Atlanta commercial buildings with adequate structural load capacity. The system's appeal was straightforward: no membrane penetrations, no adhesive, fast installation, and UV protection provided by the ballast rather than membrane formulation. Many Atlanta commercial buildings in the inner suburbs - Sandy Springs, Dunwoody, Decatur, and the industrial corridors west and south of the city - still carry ballasted EPDM systems from this era.

The practical reality of ballasted roofing in 2025 Atlanta is that most of the 1980s and 1990s inventory is at or past its service life, and the system's characteristics create specific challenges for assessment, repair, and transition. The ballast obscures the membrane surface - you cannot visually inspect a loose-laid membrane without displacing stone, and the stone prevents infrared scanning from detecting wet insulation accurately. Drain capacity is another issue: stone ballast reduces effective drain capacity and creates debris accumulation zones that Atlanta's high-intensity thunderstorms drive into drain bowls.

I do not install new ballasted systems in Atlanta. The combination of the metro's wind exposure, the structural dead-load requirement (10 to 12 pounds per square foot of ballast), and the system's long-term maintenance and transition complexity make mechanically attached or fully adhered single-ply the right choice for new Atlanta commercial work. But I assess and repair existing ballasted systems regularly, and I scope the transition from ballasted to mechanically attached or adhered systems when the existing system reaches end of life.

The moisture assessment challenge for ballasted roofs requires different technique than for exposed membrane systems. Infrared thermography - which identifies wet insulation by detecting the differential heat signature of saturated versus dry insulation - is less effective under stone ballast because the thermal mass of the stone masks the signature. We displace ballast in a grid pattern across the roof area and pull moisture cores at each exposed location. On large ballasted roofs - 50,000 to 200,000 square feet, common in the Sandy Springs and Dunwoody office parks - the core pull grid requires significant ballast displacement, which adds inspection cost and labor. That cost is necessary; ballasted roofs with wet insulation that are recovered or recoated without insulation assessment fail predictably within three to five years.

Membrane condition assessment under displaced ballast reveals the actual membrane surface - typically EPDM or early-generation TPO from the 1980s or early 1990s. Membrane body condition at this age is usually reasonable if the ballast has maintained UV protection; the failure points are at drain perimeters (where the ballast concentration is highest and water sits longest), at parapet flashings (where the loose-laid membrane terminates in a clamped or adhered flashing strip that has hardened and cracked), and at any penetrations where the membrane was cut and re-sealed.

Drain capacity under stone ballast degrades over time as fine material accumulates in the drain bowl. Atlanta's high-intensity thunderstorms deliver 2 to 3 inches per hour at peak intensity - a flow rate that overwhelms partially clogged or undersized drains and produces the standing water that accelerates ballasted membrane failure at drain perimeters. We assess and document drain condition on every ballasted roof inspection and recommend drain maintenance or replacement as part of any repair scope on a ballasted system.