Chapter 11: Storm Drainage System

Chapter 11: Storm Drainage System

Section 1101 – GENERAL

Storm drainage is required for roof areas, courts, and courtyards to collect stormwater and discharge it to an approved point of disposal that is not in conflict with other ordinances or regulations.

Section 1102 – RAINWATER SYSTEMS

1102.1 Materials:

1102.1.1 Rainwater downspouts or conductor piping placed within the interior of a building inside a vertical pipe chase or within a vent shaft shall be of cast iron, galvanized steel, iron, brass, copper, lead, Schedule 40 ABS, PVC, Series 1000, DWV, or other approved materials.

1102.1.2 Rainwater downspouts or conductor located on the exterior side of a low-height building shall be not less than 26 ga. galvanized sheet metal. The bottom of the conductor draining over the catch basin storm drain or storm sewer is protected from damage by connecting a stronger material such as steel pipe or cast iron at its lowest section.

1102.1.3 Rainwater piping located within a medium-height building basement area shall be of galvanized iron pipe, Schedule 30; cast iron soil pipe, Type DWV copper Schedule 40 ABS, DWV, Series 1000, PVC DWV, or other approved materials.

1102.1.4 Downspouts for high-rise buildings shall be of stronger pipe materials to resist the high hydrostatic pressure inside the vertical downspout installed within the pipe chase, which has no intermediate branch from the roof to the ground level.

1102.1.5 Rainwater piping commencing 0.6 meters from the exterior of a building may be of suitable approved materials permitted in the Installation Requirements of this Code.

1102.2 Connections and Installation:

1102.2.1 Rainwater piping shall not be used as soil, waste, or vent pipes.

1102.2.2 Rainwater piping installed in locations where they may be subjected to damage shall be protected.

1102.2.3 Roof drains, overflow drains, and rainwater piping used in building construction shall be previously tested and accepted in conformity with the provisions of this Code.

Section 1103 – ROOF DRAIN

1103.1 Materials:

Roof drains shall be made of cast iron, copper, or other corrosion-resistant materials.

1103.1.1 Strainers

1103.1.1.1 Roof drains shall be equipped with strainers extending not less than 25 mm above the surface of the roof immediately adjacent to the drain. Dome-Type Strainers shall have a minimum total net inlet area of one and one-half (1.5) times the area of the outlet pipe to which it is connected.

1103.1.1.2 Roof deck strainers for use on sun decks, parking decks, and similar occupied areas shall be an approved flat-surface type that is level with the deck. Such drains shall have a total net inlet area not less than two (2) times the area of the outlet pipe to which the drain is connected.

1103.1.1.3 Roof drains passing through the roof into the interior of a building shall be made watertight at the roof level by the use of a CI drain with an integral cast water stop ring around the outside of the body and at mid-depth of the concrete roof slab, and the installation of a clamped suitable flashing material around the drain.

1103.1.1.4 In all cases, the outlet connections are either welded or screwed.

Section 1104- SIZING OF RAINWATER PIPING

1104.1 Vertical rainwater piping shall be sized in accordance with Table 11-1, which is based upon the maximum depth in millimeters of rainfall per hour falling upon a given roof area in square meters. Consult local rainfall figures to determine the maximum rainfall per hour. Normally, a 102 mm/hour rainfall intensity is used around the Manila area.

1104.2 Vertical Wall Areas: Where vertical walls project above a roof so as to permit stormwater to drain to adjacent roof areas below, the total roof area considered may be computed from Table 11-2 as follows:

1104.2.1 For one (1) wall – add fifty (50) percent of the area of the wall to the roof area.

1104.2.2 For two (2) adjacent walls – add thirty-five (35) percent of the total wall areas to the roof area.

1104.2.3 For two (2) walls opposite each other and of the same heights – add no additional area to the roof.

1104.2.4 For two (2) walls opposite of differing heights – add fifty (50) percent of the wall area above the top of the lower wall to the roof area.

1104.2.5 Walls on three (3) sides – add fifty (50) percent of the area of the inner wall below the top of the lowest wall, plus allowance for the area of the wall above the top of the lowest wall per Sections 1104.2.2 and 1104.2.4.

1104.2.6 walls of four (4) sides – no allowance for wall areas below the top of the lowest wall – add for areas above the top of the lowest wall per 1104.2.1, 1104.2.2, 1104.2.4, and 1104.2.7. The area of the side of a tall building exposed to rain is taken as one-half of the gross area.

TABLE 11-1

Sizing of Roof Drains and Downspout Piping for varying Rainfall Intensities

Quantities are Horizontal Projected Roof Area in Square Meters

• Round, square, or rectangular rainwater pipes may be used and are considered equivalent when enclosing an inscribed circle equivalent to the drain leader diameter.
• For Manila and its environs, a rainfall intensity of 102 mm per hour is used.

1104.3 Horizontal Rainwater Piping: The size of a building’s rainwater piping or any of its horizontal branches shall be sized in accordance with Table 11-2, which is based upon maximum roof areas to be drained.

Find the area in the column under 127 mm and at a slope of 0.02 and read 561.1 m² (closest). Choose 152 mm as the size of leader and downspout at leftmost corner.

1104.4 Roof Gutter: The size of semi-circular bottom roof gutters shall be based on the maximum roof area, in accordance with Table 11-3.

Example: Table 11-3

Roof Area = 186 m²

Max Rainfall/hr. = 102 mm Pipe laid at 10.4 mm/m slope or s = 0.01

Find the area in the column under 102 mm rainfall intensity on the table with s = 0.01 and read 181.4 m² (as closest). Move to the left and read 177.8 mm diameter gutter.

1104.5 If the rainfall is more or less than those shown in Tables 11-2 and 11-3, then adjust the figures in the 50.8 mm rainfall by multiplying by two (2) and dividing by the maximum rate of rainfall in mm/hr.

Example: In Table 11-2, with a slope of 10.4 mm/m or s = 0.01 and a 203.2 mm rainfall, find the number of square meters a 102 mm pipe diameter will carry.

TABLE 11-2a

Size of Horizontal Rainwater Piping

TABLE 11-2b

TABLE 11-2c

TABLE 11-3a

Size of Circular Bottom Gutters

TABLE 11-3b

TABLE 11-3c

TABLE 11-3d

• Gutter has Semi-Circular bottom. Depth of equivalent area of rectangular
  gutter = 0. 392 x diameter.

TABLE 11-4

Sizing Roof Drains, Leaders, and Vertical Rainwater Piping

Notes:

1. The sizing data for vertical conductors, leaders. and drains is based on the pipes flowing 7/24 full.
2. For rainfall rates other than those listed, determine the allowable roof area by dividing the area given in the 25 mm/hour column by the desired rainfall rate.
3. Vertical piping may be round, square, or rectangular. Square pipe shall be
   sized to enclose its equivalent round pipe. Rectangular pipe shall have at least the same cross-sectional area as its equivalent round pipe, except that the ratio of its side dimensions shall not exceed 3 to 1.

TABLE 11-5a

Size of Gutters

TABLE 11-5b

• Width of Rectangular Gutter = 0.8862 x Diameter.

TABLE 11-5c

TABLE 11-5d

• Width of Rectangular Gutter = 0.8862 x Diameter.