How To Remove Loose Gravel off a Commercial Roof?

Gravel built-up roofs (BUR) can't be coated or restored without first removing the gravel layer. Here's how it's done and what to expect.

Why Gravel Must Be Removed

Gravel provides ballast and UV protection for the underlying BUR membrane, but it prevents any restoration coating or spray foam from adhering properly to the substrate. The irregular, jagged surface also makes it impossible to install a sheet membrane overlay without a cover board. Gravel removal is a required first step for any non-replacement restoration approach.

Method 1: Hydro-Vacuuming (Preferred)

Hydro-vacuuming uses high-pressure water and a vacuum system to loosen and remove gravel without damaging the underlying membrane. It's the fastest and least damaging method, preserving the existing BUR substrate for foam bonding. Cost is typically $0.50–$1.00 per square foot depending on gravel depth and roof accessibility.

Method 2: Mechanical Sweeping

Some contractors use mechanical sweepers or blowers to push gravel to the roof edges for collection. This is less precise than hydro-vacuuming and can leave more residual gravel on the surface, requiring additional cleanup.

After Gravel Removal

Once gravel is removed, the existing BUR substrate is inspected for moisture and condition. If the substrate is in acceptable condition (under 25% wet insulation), spray foam can be applied directly to it — the existing BUR provides an ideal bonding surface for the foam.