gravel stop

A gravel stop is a strip of metal flashing, typically 4 to 6 inches tall, installed around the perimeter edge of a built-up or gravel-surfaced roof. Its purpose is to contain the loose stone aggregate that forms the top weathering layer, preventing it from washing off during heavy rain, wind, or from being kicked off during maintenance work. The flashing also acts as a transition between the roof plane and the roof edge, directing water back onto the membrane rather than allowing it to run behind the edge and saturate the underlying structure.

Gravel stops are made from galvanized steel, aluminum, or occasionally stainless steel. The vertical face of the stop sits proud of the roof surface, while the horizontal base is embedded into the roofing membrane or fastened to the roof deck. The top edge is often hemmed or coped to prevent sharp edges. Standard profiles have an approximately 90-degree angle between the vertical and horizontal sections, though some designs slope inward slightly to better shed water back onto the roof field.

Common problems and installation considerations

Gravel stops often fail when they are undersized relative to the depth of aggregate used, allowing stones to spill over during heavy storms or when roof areas are walked upon. Poor attachment to the roof edge, using only adhesive rather than mechanical fasteners, leads to separation and water infiltration behind the flashing. The junction between the gravel stop and the membrane is a critical detail: the membrane must be turned up and sealed against the horizontal base, not merely lapped under it. Movement due to thermal expansion, especially with aluminum stops in climates with large temperature swings, can tear the membrane seal if the flashing is fastened too rigidly.

Gravel stops are used almost exclusively on low-slope roofs, which typically carry aggregate surfacing for UV protection and to add mass for wind resistance. They are less common on flat roofs with membrane surfacing alone. The term reflects the historical dominance of gravel as the protective layer on these roofs, even though modern specifications may call for slag, crushed stone, or other aggregates.

In roof system design and specifications, the gravel stop is often treated as a minor detail, but its failure is a leading cause of water damage in roof perimeters. Building codes address it indirectly through requirements for edge flashings and water management, but specific gravel stop design is usually left to the roofing trade's standard practices. Proper sizing, material selection, and careful membrane integration at the gravel stop base are essential to avoid costly repairs to underlying insulation and structural framing.