Ballasted Mount

A ballasted mount is a solar panel racking system that uses heavy weights — typically concrete blocks or precast concrete trays — to hold panels in place on a flat roof without penetrating the roof membrane. The weight of the ballast resists wind uplift forces, eliminating the need to bolt through the waterproof roofing layer and the risk of leaks at penetration points.

Ballasted systems are the standard mounting method for flat commercial roofs with TPO, PVC, EPDM, or built-up roofing membranes. These membranes are expensive to repair if penetrated, and building owners strongly prefer non-penetrating installation methods that preserve the roof warranty.

The racking typically consists of low-profile tilted trays or frames that hold panels at 5-15° tilt — steep enough for rainwater runoff and moderate energy optimization but shallow enough to minimize wind loading. Concrete ballast blocks sit on the trays or at strategic points along the array, with the total weight calculated by a structural engineer based on local wind speed, building height, roof edge proximity, and roof structural capacity.

Ballast weight requirements can be substantial — a typical ballasted commercial array might add 3-6 pounds per square foot of dead load to the roof structure. The structural engineer must verify that the building's roof framing can support this additional weight in combination with existing dead loads (roofing materials, HVAC equipment) and live loads (snow, maintenance personnel).

Ballasted mounts are rarely used on residential sloped roofs because the panels would slide under gravity. They are also less suitable in extreme wind zones where the ballast weight required would exceed the roof's structural capacity. In these cases, a hybrid approach using minimal penetrations combined with reduced ballast may be engineered.