Gravel Ballast Roof

Ballast should consist of washed, well rounded gravel graded between 20mm to 40mm size. Fines and sharps must be excluded, fines particularly can cause blockage of drains. Gravel of this size is required to mitigate the onset of ‘wind scour’; BRE Digest 311 refers.

Note that we do not recommend the use of gravel adhesive as experience has shown it only remains effective for a few short years.

• Gravel must be laid to meet the twin minimum requirements of 80kg/m2 and 50mm thickness.
• Gravel ballast is only suitable for very low pitches of roof slope.
• Gravel ballast is not suitable for foot traffic, therefore pavers would normally be used to create walkways if required.

Where the degree of roof exposure is high the gravel ballast can be lifted out by wind uplift forces in the worst conditions, especially when adjacent to parapets, in these cases it is advisable to have pavers rather than gravel around the margins of the roof area.