The Ontario Building Code | Hydraulic Loads on Horizontal Storm Drains
7.4.10.9. Hydraulic Loads on Horizontal Storm Drains
(1) The hydraulic load that is drained to a horizontal storm drainage pipe shall conform to Table 7.4.10.9., based on the size and slope.
Table 7.4.10.9.
Maximum Permitted Hydraulic Load Drained to a Horizontal Storm drainage Pipe
Forming Part of Sentences 7.4.10.9.(1) and 7.4.10.10.(2)
| Item | Column 1 | Column 2 | Column 3 | Column 4 | Column 5 | Column 6 | Column 7 | Column 8 |
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| Size of Drain or Sewer, in. | Maximum Hydraulic Load, L |
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| Slope(1) |
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| 1 in 400 | 1 in 200 | 1 in 133 | 1 in 100 | 1 in 68 | 1 in 50 | 1 in 25 |
| 1. | 3 | ------ | ------ | ------ | ------ | ------ | 2 770 | 3 910 |
| 2. | 4 | ------ | ------ | ------ | 4 220 | 5 160 | 5 970 | 8 430 |
| 3. | 5 | ------ | ------ | 6 760 | 7 650 | 9 350 | 10 800 | 15 300 |
| 4. | 6 | ------ | ------ | 10 700 | 12 400 | 15 200 | 17 600 | 24 900 |
| 5. | 8 | ------ | 18 900 | 23 200 | 26 700 | 32 800 | 37 800 | 53 600 |
| 6. | 10 | ------ | 34 300 | 41 900 | 48 500 | 59 400 | 68 600 | 97 000 |
| 7. | 12 | 37 400 | 55 900 | 68 300 | 78 700 | 96 500 | 112 000 | 158 000 |
| 8. | 15 | 71 400 | 101 000 | 124 000 | 143 000 | 175 000 | 202 000 | 287 000 |
Notes to Table 7.4.10.9.:
(1) Slope is the ratio of rise to run, in whatever measurement units are chosen.
In Plain Language
Horizontal storm drains have their own maximum hydraulic load table based on pipe size and slope, reflecting that storm flow calculations differ from sanitary sewage flow calculations.
This is a plain-language summary of the 2012/2017 Ontario Building Code text above, for general understanding only and not a substitute for the Code. Always confirm current requirements against the 2024 edition (O.Reg. 163/24) or a qualified professional before construction.