Gutters and Downspouts:
Roof Sumps and Drains

Description: Copper roof sumps are generally used for draining small roof areas such as canopies. Their size depends on the roof area, the numbers of roof sumps used on the roof, the drainage outlet size, and the location of the sump on the roof.

The form of the roof sump should conform to the form of the roof. On a roof composed of a series of arches, for example, roof sumps should be placed in the valleys between the arches. The flange should conform to the shape of the arches.

Roof sump drains are not recommended for use as a general roof drainage system.

Special Conditions: Formed copper roof sumps may also be used on flat roofs with copper flat seam construction. The details differ in that gravel stops are not required, and the horizontal flanges of the sump are joined to the copper roofing with soldered flat seams.

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A. Formed Roof Sump at Parapet Wall This detail illustrates the installation of a roof sump at the corner formed by parapet walls.

Wood framing for the curb around the sump is provided as required. The horizontal flanges should be a maximum 4" wide and should be fastened to the roof through the roofing felts.

Vertical flanges of 8" minimum are provided on the sides of the roof sump and fastened to the wall with brass screws and lead shields. The top edges of the vertical flanges are lapped by counterflashing. The brass screws should be overlapped by the flashing.

Water collected in the sump is drained through an outlet tube into the downspout or other drainage stack. An outlet tube strainer is installed to minimize clogging. The use of a 1/2", minimum, copper or copper alloy mesh removable screen is also suggested. The top of the screen should be a minimum of 4" above the roof level.

Gravel stop angles are notched and soldered onto the horizontal sump flange to prevent gravel and tar from entering the drain.

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B. Prefabricated Roof Drain This detail shows a prefabricated copper roof drain installed in a steel deck. Wood blocking is required for support of the 48 oz. copper drain flange. The copper roof pan is fastened to the flange with a continuous soldered joint. A prefabricated bronze strainer is shown.