Minnesota Administrative Rules
Agency 151 - Labor and Industry Department
Chapter 1305 - ADOPTION OF INTERNATIONAL BUILDING CODE
Part 1305.1503 - SECTION 1503, WEATHER PROTECTION

1. Where required. All roofs shall drain into a separate storm sewer system or to an approved place of disposal. For one- and two-family dwellings, and where approved, storm water is permitted to discharge onto flat areas, such as streets or lawns, provided that the storm water flows away from the building.

2. Roof design. Roofs shall be 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.

3. 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.

4. 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.

5. Sizing of secondary drains. Secondary (emergency) roof drain systems shall be sized in accordance with the Minnesota State Plumbing Code. 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 dimension of less than 4 inches (102 mm). The flow through the primary system shall not be considered when sizing the secondary roof drainage system.