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// CODE SNIPPET

1101.8 Areaway Drains

California Plumbing Code 2016 > 11 Storm Drainage > 1101.0 General > 1101.8 Areaway Drains
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Open subsurface space adjacent to a building, serving as an entrance to the basement or cellar of a building, shall be provided with a drain or drains. Such areaway drains shall be not less than 2 inches (50 mm) in diameter for areaways at a maximum of 100 square feet (9.29 m2) in area, and shall be discharged in the manner provided for subsoil drains not serving continuously flowing springs or groundwater (see Section 1101.6.1). Areaways in excess of 100 square feet (9.29 m2) shall not drain into subsoil drains. Areaway drains for areaways exceeding 100 square feet (9.29 m2) shall be sized in accordance with Table 1101.8.
TABLE 1101.8
SIZING OF HORIZONTAL RAINWATER PIPING1, 2
SIZE OF PIPE FLOW
(1/8 inch per foot
slope)
MAXIMUM ALLOWABLE HORIZONTAL PROJECTED ROOF AREAS
AT VARIOUS RAINFALL RATES
(square feet)
inches gpm 1 (in/h) 2 (in/h) 3 (in/h) 4 (in/h) 5 (in/h) 6 (in/h)
3 34 3288 1644 1096 822 657 548
4 78 7520 3760 2506 1880 1504 1253
5 139 13360 6680 4453 3340 2672 2227
6 222 21400 10700 7133 5350 4280 3566
8 478 46000 23000 15330 11500 9200 7670
10 860 82800 41400 27600 20700 16580 13800
12 1384 133200 66600 44400 33300 26650 22200
15 2473 238000 119000 79333 59500 47600 39650

SIZE OF PIPE FLOW
( 1/4 inch per foot
slope)
MAXIMUM ALLOWABLE HORIZONTAL PROJECTED ROOF AREAS
AT VARIOUS RAINFALL RATES
(square feet)
inches gpm 1 (in/h) 2 (in/h) 3 (in/h) 4 (in/h) 5 (in/h) 6 (in/h)
3 48 4640 2320 1546 1160 928 773
4 110 10600 5300 3533 2650 2120 1766
5 196 18880 9440 6293 4720 3776 3146
6 314 30200 15100 10066 7550 6040 5033
8 677 65200 32600 21733 16300 13040 10866
10 1214 116800 58400 38950 29200 23350 19450
12 1953 188000 94000 62600 47000 37600 31350
15 3491 336000 168000 112000 84000 67250 56000

SIZE OF PIPE FLOW
( 1/2 inch per foot
slope)
MAXIMUM ALLOWABLE HORIZONTAL PROJECTED ROOF AREAS
AT VARIOUS RAINFALL RATES
(square feet)
inches gpm 1 (in/h) 2 (in/h) 3 (in/h) 4 (in/h) 5 (in/h) 6 (in/h)
3 68 6576 3288 2192 1644 1310 1096
4 156 15040 7520 5010 3760 3010 2500
5 278 26720 13360 8900 6680 5320 4450
6 445 42800 21400 14267 10700 8580 7140
8 956 92000 46000 30650 23000 18400 15320
10 1721 165600 82800 55200 41400 33150 27600
12 2768 266400 133200 88800 66600 53200 44400
15 4946 476000 238000 158700 119000 95200 79300
For SI units: 1 inch = 25 mm, 1 gallon per minute = 0.06 L/s, 1/8 inch per foot = 10.4 mm/m, 1 inch per hour = 25.4 mm/h, 1 square foot = 0.0929 m2

Notes:
1   The sizing data for horizontal piping are based on the pipes flowing full.
2   For rainfall rates other than those listed, determine the allowable roof area by dividing the area given in the 1 inch per hour (25.4 mm/h) column by the desired rainfall rate.

Related Code Sections


1101.8 Storm Drainage, Areaway Drains
or drains. Such areaway drains shall be not less than 2 inches (50 mm) in diameter for areaways at a maximum of 100 square feet (9.29 m 2 ) in area, and shall ...
California Plumbing Code 2016 > 11 Storm Drainage > 1101.0 General > 1101.8 Areaway Drains
1101.8 Storm Drainage, Areaway Drains
or drains. The areaway drains shall be not less than 2 inches (50 mm) in diameter for area ways at a maximum of 100 square feet (9.29 m 2 ) in area, and shall ...
California Plumbing Code 2019 > 11 Storm Drainage > 1101.0 General > 1101.8 Areaway Drains
1101.0 Storm Drainage, General
in Section 1101.6 shall prevent drains that serve either subsoil drains or areaways of a detached building from discharging to a properly graded open area ...
California Plumbing Code 2019 > 11 Storm Drainage > 1101.0 General
1101.6 Storm Drainage, Subsoil Drains
Nothing in Section 1101.6 shall prevent drains that serve either subsoil drains or areaways ...
California Plumbing Code 2016 > 11 Storm Drainage > 1101.0 General > 1101.6 Subsoil Drains
1101.6 Storm Drainage, Subsoil Drains
Nothing in Section 1101.6 shall prevent drains that serve either subsoil drains or areaways ...
California Plumbing Code 2019 > 11 Storm Drainage > 1101.0 General > 1101.6 Subsoil Drains
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