Minn. R. 1305.1502 - SECTION 1502, ROOF DRAINAGE

Subpart 1. IBC section 1502.1.

IBC section 1502.1 is amended and subsections are added to read as follows:

1502.1 Roof drainage. Design and installation of roof drainage systems shall comply with Minnesota Rules, chapter 4714, Minnesota Plumbing Code, and the following provisions:
1502.1.1 Where required. All roofs shall drain into a separate storm sewer system or to an approved place of disposal.
1502.1.2 Roof design. Roofs shall be structurally designed for the maximum possible depth of water that will pond thereon as determined by the relative levels of roof deck and overflow weirs, scuppers, edges, or serviceable drains in combination with the deflected structural elements. In determining the maximum possible depth of water, all primary roof drainage means shall be assumed to be blocked.
Subp. 1a. IBC section 1502.2.

IBC section 1502.2 is amended and subsections and Table 1502.2.3 are added to read as follows:

1502.2 Secondary drainage required. Secondary (emergency) roof drains or scuppers shall be provided where the roof perimeter construction extends above the roof in such a manner that water will be entrapped if the primary drains allow buildup for any reason.
1502.2.1 Separate systems required. Secondary (emergency) roof drain systems shall have piping and point of discharge separate from the primary system. Discharge shall be above grade in a location which would normally be observed by the building occupants or maintenance personnel.
1502.2.2 Sizing of secondary drains. Secondary (emergency) roof drain systems shall be sized to the same capacity as the primary roof drain areas in accordance with Minnesota Rules, chapter 4714, the Minnesota Plumbing Code.
1502.2.3 Sizing of scuppers. Scuppers shall be sized to prevent the depth of ponding water from exceeding that for which the roof was designed as determined by this code. Scuppers shall not have an opening weir length dimension of less than 4 inches (102 mm) and shall be sized in accordance with Table 1502.2.3. The flow through the primary system shall not be considered when sizing the secondary roof drainage system.


Square feet of Roof Area
Head Height in Inchesb Length of Weir in inches
4 6 8 12 16 20 24
1 273 418 562 851 1139 1427 1715
2 734 1141 1549 2365 3180 3996 4813
3 1274 2023 2772 4270 5768 7267 8766
4 1845 2999 4152 6460 8766 11073 13381
6 2966 5087 7204 11442 15860 19918 24160

a Table based upon 4-inch per hour rainfall.

b Minimum 1-inch vertical free space above Head (H) is required.

Subp. 2. IBC section 1502.3.

IBC section 1502.3 is deleted in its entirety.


IBC section 1510.2.2 is amended to read as follows:

1510.2.2 Use limitations. Penthouses shall not be used for purposes other than shelter of mechanical or electrical equipment, tanks, or vertical shaft openings in the roof assembly.

Exception: Accessory uses necessary for the maintenance of building systems shall be permitted when the penthouse is sprinkled in accordance with Section 903.1.1.


Minn. R. 1305.1502
39 SR 1605; 44 SR 609 effective 3/31/2020

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