Inspecting Commercial Ballasted Roof

The ballasted roof shown in the video is from a 12-story office building inspection. To learn more about inspecting ballasted and low-slope roof systems, take the self-paced Inspecting Commercial Low-Slope Roofs Online Course and earn your certificate upon completion.The roof inspection includes assessing surface conditions, drainage, ponding, and for visible defects. For single-ply and ballasted systems, a key factor is looking for irregularities, such as:

• Uneven or displaced ballast coverage and depth (typically one to two layers of rock)
• Improper ballast materials that may damage or puncture the membrane
• Low or spongy spots and depressions
• Raised sections that may indicate trapped moisture or insulation movement
• Areas of ponding and staining or debris patterns
• Clogged drains or missing strainers for built-in drains
• Blistering, alligatoring, loose or open seams, punctures, cracking, or splitting in exposed membrane areas
• Missing or insufficient flashing at parapets and roof penetrations
• Sections that appear patched or different from surrounding areas
• Areas needing repair or areas under repair

What Is a Ballasted Roof?

A ballasted roof is a low-slope roofing system where the waterproof membrane is held in place by loose materials, typically smooth stones, concrete pavers, or similar ballast. The ballast protects the underlying membrane from UV exposure, thermal cycling, and wind uplift. At the 12-story office building inspection, river rock was the primary ballast material, with concrete pavers used to create walking paths. The pavers provide stable footing and concentrated weight distribution around the building perimeter, while the river rock covers most of the roof surface.

“Ballast” refers to protective material placed over the roofing membrane. It’s important for inspectors to distinguish between river rock (smooth, rounded stones without sharp edges) and gravel (angular stones with sharp edges). Ballast should be smooth to prevent membrane abrasion or puncture from movement or foot traffic. The presence of sharp-edged gravel should be documented as a potential concern.

Inspection Limitations

Since the ballast should evenly cover the roof surface without exposed membrane, this roofing system presents inspection challenges due to limited visibility. Some inspectors note this limitation in their reports. Others may move ballast in select areas to observe the condition of the membrane, although not required by the ComSOP.

Inspectors should check for exposed membrane at roof corners from wind scouring and around penetrations, such as skylights, drains, and equipment. Document significant ballast movement and identify the membrane type and condition when visible. When inspecting the interior, assess the underside of the roof for stains on ceiling tiles and exposed decking or insulation in unfinished areas.

Learn more about inspecting low-slope roofs in the Inspecting Low-Slope Roofs Online Course for Commercial Property Inspectors. It’s a self-paced course that includes a coursebook, inspection checklists and field guides, and a downloadable certificate upon successful completion.