Minnesota Legislature
Office of the Revisor of Statutes
Minnesota Administrative Rules
4715.2710 SIZE OF BUILDING STORM DRAINS AND LEADERS.
Subpart 1.
Size of building storm drain.
The size of the building storm drain or any of its horizontal branches having a slope of one-half inch or less per foot, shall be based upon the maximum projected roof or paved area to be handled according to subpart 4.
Subp. 2.
Size of vertical leaders.
Vertical leaders shall be sized on the maximum projected roof area, according to subpart 5.
Subp. 3.
Reduction in size prohibited.
Storm drain piping shall not reduce in size in the direction of flow, including changes in direction from horizontal to vertical.
Subp. 4.
Size of horizontal storm drains.
| Diameter of Drain | Maximum Projected Roof Area for Drains of Various Slopes | ||
| Inches | 1/8 in. Slope | 1/4 in. Slope | 1/2 in. Slope |
| Square Feet | Square Feet | Square Feet | |
| 3 | 822 | 1,160 | 1,644 |
| 4 | 1,880 | 2,650 | 3,760 |
| 5 | 3,340 | 4,720 | 6,680 |
| 6 | 5,350 | 7,550 | 10,700 |
| 8 | 11,500 | 16,300 | 23,000 |
| 10 | 20,700 | 29,200 | 41,400 |
| 12 | 33,300 | 47,000 | 66,600 |
| 15 | 59,500 | 84,000 | 119,000 |
Use a rate of rainfall of four inches per hour for sizes not listed in this table.
Subp. 5.
Size of vertical leaders.
| Size of Leader or Conductor Inches |
Maximum Projected Roof Area Square Feet |
| 2 | 720 |
| 2-1/2 | 1,300 |
| 3 | 2,200 |
| 4 | 4,600 |
| 5 | 8,650 |
| 6 | 13,500 |
| 8 | 29,000 |
Use a rate of rainfall of four inches per hour for sizes not listed in this table.
The equivalent diameter of square or rectangular leader may be taken as the diameter of that circle which may be inscribed within the cross-sectional area of the leader.
Subp. 6.
Values for continuous flow.
If there is a continuous or semicontinuous discharge into the building storm drain or building storm sewer, as from a pump, ejector, or similar device, each gallon per minute of the discharge must be computed as being equivalent to 24 square feet of roof area, based upon a four-inch rainfall.
Statutory Authority:
MS s 16B.59 to 16B.75; 326.37 to 326.45; 326B.101 to 326B.194; 326B.43 to 326B.49
History:
23 SR 686; L 2007 c 140 art 4 s 61; art 6 s 15; art 13 s 4; L 2008 c 337 s 64; 33 SR 2042
Published Electronically:
May 14, 2012
Official Publication of the State of Minnesota
Revisor of Statutes