1101.8 Areaway Drains

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 PIPING^{1, 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.