Ballasted Roof Ballast Weight and Order
The weight and order quantity of loose ballast on a ballasted single-ply (EPDM / TPO) low-slope roof. Total dead load = roof area x ballast rate: 5,000 sf at 12 psf = 60,000 lb (30 tons). Stone is ordered by the yard, so volume = weight / bulk density (~90-105 pcf river gravel) / 27 = 22.2 cu yd, ~1.4 in deep. The BALLAST RATE is set by ANSI/SPRI RP-4 from the building height, roof-edge/parapet condition, and wind zone: often 10 psf (nominal 1,000 lb/square) of smooth #4 river gravel in the field, rising to ~13-15 psf or concrete pavers at the corners and perimeter and on taller/higher-wind buildings. A dead-load and ordering SCREEN, not a wind-uplift design; RP-4 and the structural engineer set the rate and zone layout, and the deck capacity governs.
Formula and source
total_ballast_lb = roof_area_sqft x ballast_psf; total_tons = total_ballast_lb / 2000; stone_depth_in = ballast_psf / stone_density_pcf x 12; volume_cy = total_ballast_lb / stone_density_pcf / 27.
Ballasted single-ply roof ballast weight and order quantity (ANSI/SPRI RP-4 ballast rates), by name; RP-4 and the structural engineer set the ballast rate and zone layout, and the deck capacity governs.
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