Drainage sizing: slope, length, pipe size and hydraulic loads (Plumbing

Last updated October 22, 2026

Values this chapter turns on

flat storm load for 260 fixture units or fewer: 2,360 L; flat storm load for 260 fixture units or fewer
storm load per fixture unit above 260: 9.1 L; storm load per fixture unit above 260
min slope of drainage pipe NPS 3 or smaller: 1 in 50; min slope of drainage pipe NPS 3 or smaller
max design fill of a vertical sanitary pipe: 29%; max design fill of a vertical sanitary pipe

Sizing is where the All Buildings exam earns its calculation marks. The house version of this topic stops at a few bathrooms and a downspout. Here you size stacks for apartment towers, building drains for a few thousand fixture units, storm drains for large flat roofs and parking lots, and combined sewers that carry both. The method never changes: total the load, pick the table that matches the pipe's job, then apply the minimum size rules that override the table.

Slope and length

Drainage pipes of NPS 3 or less slope at least 1 in 50 (OBC Div. B 7.4.8.1.). A force main is exempt, and a flatter slope is allowed only if it still gives at least 0.6 m/s gravity flow. Larger pipes can run at any slope the sizing tables list. A fixture outlet pipe is limited to 1,200 mm developed length, except for grouped floor drains, showers and similar fixtures on one trap (7.4.8.2.).

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Rules that beat the tables

Rule	Where
A minimum-size pipe cannot drain into a smaller one (heat recovery units excepted for non-solid waste)	7.4.9.1.
A drain passing through a wall or floor to a stack keeps full size	7.4.9.1.
Pipe serving a water closet: NPS 3 minimum	7.4.9.2.
Branch or building drain downstream of the third water closet: NPS 4 minimum	7.4.9.2.
Stack serving more than 6 water closets: NPS 4 minimum	7.4.9.2.
Building drain and sewer downstream of the main cleanout, and every storm building drain and sewer: NPS 4 minimum	7.4.9.4.
Common outlet of a 3-compartment sink: one size larger than the largest compartment outlet	7.4.9.3.
Leader offset under the roof, 6 m or less, at 1 in 50 or steeper: no size change; longer offsets are sized as a storm drain	7.4.9.5.

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What counts in the load

The load on a pipe is everything upstream: connected fixtures, fixtures with provision for future connection, and all roofs and paved surfaces draining to it (OBC Div. B 7.4.10.1.). Loads come from four places:

Listed fixtures take the fixture units in Table 7.4.9.3.. Commercial fixtures matter on this exam: flush valve water closets, the different urinal types, commercial dishwashers, potato peelers and multi-head showers each have their own row.
Unlisted fixtures take a load from their trap size in Table 7.4.10.2..
Continuous flow (a pump or air conditioning unit) is 31.7 fixture units per L/s on a sanitary system, but 900 L per L/s where it drains to a storm or combined sewer (7.4.10.3.). Semi-continuous flows use Table 7.4.10.12. by trap size and flow band.
Roofs and paved surfaces: the 15 minute rainfall from SB-1 (in mm) multiplied by the horizontal projected area plus half of the largest adjoining vertical wall, in m². Millimetres times square metres gives litres (7.4.10.4.).

To put fixture units into a storm or combined calculation, convert them to litres (7.4.10.5.): any total of 260 fixture units or fewer counts as a flat 2,360 L, and above 260 each fixture unit is 9.1 L.

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Which table for which pipe

Pipe	Table	Read it by
Stack (no long offset)	7.4.10.6.-A	total load and the per-storey limit
Branch	7.4.10.6.-B	total load
Sanitary building drain or sewer	7.4.10.6.-C	load and slope
Stack with an offset of 1.5 m or more	7.4.10.6.-B or -C, whichever is less restrictive	load (and slope)
Storm or combined building drain or sewer	7.4.10.9.	litres and slope
Roof gutter	7.4.10.10.	litres and slope
Leader	7.4.10.11.	litres, circular or non-circular

Design limits behind the tables: a vertical sanitary pipe runs at no more than 29% full (7.4.10.6.), a horizontal one at no more than 65% full (7.4.10.8.).

Always choose the smallest pipe whose tabulated value is equal to or greater than your load, at a slope you will actually build. If your slope is between two columns, use the flatter one.

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Worked example 1: office washroom branch

Fixtures on one branch: 3 water closets with direct flush valves (6 each = 18), 2 wall washout urinals (1½ each = 3), 3 domestic-type lavatories with NPS 1¼ traps (1 each = 3), and one floor drain with an NPS 2 trap (2). Total = 26 fixture units.

Table 7.4.10.6.-B allows 27 on an NPS 3 branch, so the load alone says NPS 3. But the branch is downstream of the third water closet, so 7.4.9.2. forces NPS 4. The override wins.

Worked example 2: apartment stack

A 10-storey building has, on each floor, 2 bathroom groups with flush tanks (6 each), 2 domestic kitchen sinks (1½ each) and 2 domestic clothes washers (1½ each): 18 fixture units per storey, 180 in total.

On Table 7.4.10.6.-A, NPS 3 allows 102 total and 18 per storey, so the total fails. NPS 4 allows 540 total and 100 per storey: it passes. The stack also serves 20 water closets, more than 6, so NPS 4 is required anyway.

Worked example 3: building drain and slope

A building drain carries 800 fixture units. On Table 7.4.10.6.-C at 1 in 100, NPS 6 allows 700 (too small) and NPS 8 allows 1,600, so NPS 8. Steepen it to 1 in 50 and NPS 6 allows 840, so NPS 6 works. Slope buys pipe size.

Worked example 4: flat roof storm drain and leaders

A roof is 40 m by 30 m (1,200 m²). A wall rises 6 m above the roof along the 30 m side (180 m²), so half of it, 90 m², is added. Assume SB-1 gives a 15 minute rainfall of 25 mm.

Load = 25 × (1,200 + 90) = 32,250 L.

Storm building drain, Table 7.4.10.9.: at 1 in 100, NPS 8 carries 26,700 L (too small) and NPS 10 carries 48,500 L, so NPS 10. At 1 in 50, NPS 8 carries 37,800 L, so NPS 8.

Four equal leaders share the roof: 32,250 / 4 = about 8,063 L each. Table 7.4.10.11. gives 5,000 L for a circular NPS 3 and 10,800 L for NPS 4, so each leader is NPS 4.

Worked example 5: combined sewer

A combined building sewer takes 300 fixture units plus a 2,000 m² parking lot, with 25 mm of rainfall. The fixtures are over 260, so 300 × 9.1 = 2,730 L. The lot gives 25 × 2,000 = 50,000 L. Total 52,730 L. At 1 in 100, NPS 10 carries 48,500 L (fails) and NPS 12 carries 78,700 L, so NPS 12. At 1 in 50, NPS 10 carries 68,600 L.

If the same sewer took only 120 fixture units, the sanitary part would be the flat 2,360 L, not 120 × 9.1.

Continuous flow

A 0.5 L/s cooling discharge to a sanitary drain adds 0.5 × 31.7 = 15.85 fixture units. The same flow to a storm sewer adds 0.5 × 900 = 450 L.

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Flow control roof drains

Large flat roofs often use flow control drains (7.4.10.4.). Conditions: drain down within 24 h, a roof designed for the stored water, scuppers not more than 30 m apart that handle up to 200% of the 15 minute rainfall and cap ponding at 150 mm, drains within 15 m of the roof edge and 30 m of each other, and at least one drain per 900 m². A parapet over 150 mm high (or higher than the wall flashing) requires overflows or scuppers and at least 2 roof drains.

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Common traps

Using the branch table for a stack, or the stack table for a building drain. Match the pipe's job.
Forgetting the per-storey column on the stack table.
Converting 200 fixture units as 200 × 9.1 L. At 260 or fewer the answer is 2,360 L.
Forgetting half of the adjoining wall on a roof calculation, or adding the whole wall.
Using 31.7 fixture units per L/s for a flow that goes to a storm sewer.

Chapter review

Chapter at a glance

One line per section: the idea to carry into the exam. Then the answers that most often catch candidates out.

Chapter at a glance: the key idea in each section
Section	Key idea
Slope and length	Drainage pipes of NPS 3 or less slope at least 1 in 50. A force main is exempt, and a flatter slope is allowed only if it still gives at least 0.6 m/s gravity flow.
What counts in the load	The load on a pipe is everything upstream: connected fixtures, fixtures with provision for future connection, and all roofs and paved surfaces draining to it.
Which table for which pipe	Design limits behind the tables: a vertical sanitary pipe runs at no more than 29% full, a horizontal one at no more than 65% full.
Continuous flow	A 0.5 L/s cooling discharge to a sanitary drain adds 0.5 × 31.7 = 15.85 fixture units.
Flow control roof drains	Large flat roofs often use flow control drains.

Slope and length
Drainage pipes of NPS 3 or less slope at least 1 in 50. A force main is exempt, and a flatter slope is allowed only if it still gives at least 0.6 m/s gravity flow.
What counts in the load
The load on a pipe is everything upstream: connected fixtures, fixtures with provision for future connection, and all roofs and paved surfaces draining to it.
Which table for which pipe
Design limits behind the tables: a vertical sanitary pipe runs at no more than 29% full, a horizontal one at no more than 65% full.
Continuous flow
A 0.5 L/s cooling discharge to a sanitary drain adds 0.5 × 31.7 = 15.85 fixture units.
Flow control roof drains
Large flat roofs often use flow control drains.

Usual exam traps

Using the branch table for a stack, or the stack table for a building drain. Match the pipe's job.
Forgetting the per-storey column on the stack table.
Converting 200 fixture units as 200 × 9.1 L. At 260 or fewer the answer is 2,360 L.
Forgetting half of the adjoining wall on a roof calculation, or adding the whole wall.
Using 31.7 fixture units per L/s for a flow that goes to a storm sewer.

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Questions on Drainage sizing: slope, length, pipe size and hydraulic loads, in the exam format, every answer explained and cited to its article. Sign in to start; a free account gets the free questions.

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Code cited in this chapter

Based on the official 2024 Building Code Compendium on ontario.ca.

OBC Div. B 7.4.8.1. Minimum Slope
(1)Except as provided in Sentences (2) and (3) and Articles 7.4.10.8. and 7.4.10.9., drainage pipes that are NPS 3 or less shall have a downward slope in the direction of flow of at least 1 in 50. (See Note A-7.4.8.1.(1))
(2)Sentence (1) does not apply to a force main.
(3)Where it is not possible to comply with Sentence (1), a lesser slope may be used if it will produce a gravity flow of not less than 0.6 m per second.
Open OBC Div. B 7.4.8.1. in the code viewer
OBC Div. B 7.4.8.2. Length of Fixture Outlet Pipes
(1)Except for fixture outlet pipes installed in conformance with Sentence 7.4.5.1.(3), the developed length of fixture outlet pipes shall not exceed 1,200 mm.
Open OBC Div. B 7.4.8.2. in the code viewer
OBC Div. B 7.4.9.1. No Reduction in Size
(1)Except as permitted in Sentence (3), no drainage pipe that is of minimum size required by this Part for the purpose for which it is installed shall be so connected as to drain to other drainage pipe of lesser size.
(2)Where a building drain connects to a stack through a wall or floor, the drain shall retain its full size through the wall or floor.
(3)A sanitary drainage pipe may be connected to a pre-engineered waste water heat recovery system that incorporates piping of a lesser size than required by Sentence (1) provided that it does not convey sewage
(a)from a sanitary unit, or
(b)that contains solids.
Open OBC Div. B 7.4.9.1. in the code viewer
OBC Div. B 7.4.9.2. Serving Water Closets
(1)Drainage pipes that serve a water closet shall be not less than NPS 3.
(2)Branch and building drains downstream of the third water-closet fixture drain connection shall be not less than NPS 4.
(3)Stacks that serve more than 6 water closets shall be not less than NPS 4.
(4)Discharge pipes serving a macerating toilet system shall be not less than NPS 3/4 .
(5)No vertical leg of the drainage pipe from a water closet or other fixture that has an integral siphonic flushing action shall exceed 1,000 mm.
Open OBC Div. B 7.4.9.2. in the code viewer
OBC Div. B 7.4.9.4. Minimum Size of Building Drain and Sewer
(1)Building drains and building sewers connected to the public sewer system downstream of the main cleanout (see Sentence 7.4.7.1.(6)) shall be not less than NPS 4.
(2)Storm building drains and storm building sewers shall be not less than NPS 4.
Open OBC Div. B 7.4.9.4. in the code viewer
OBC Div. B 7.4.9.3. Size of Fixture Outlet Pipes
(1)Except as provided in Sentence (2), the nominal pipe size of fixture outlet pipes shall conform to Table 7.4.9.3.
(2)The part of the fixture outlet pipe that is common to 3 compartments of a sink shall be one NPS larger than the largest fixture outlet pipe of the compartments that it serves. (See Note A-7.4.9.3.(2))
(3)Where clothes washers do not drain to a laundry tray, the trap inlet shall be not less than NPS 2 and be fitted with a vertical standpipe that is not less than 600 mm long measured from the trap weir and terminates above the flood level rim of the clothes washer. (See Note A-7.4.9.3.)
(4)In an individual dwelling unit, where multiple shower heads are served by one shower receptacle, the fixture outlet pipe shall be not less than NPS 2.
Open OBC Div. B 7.4.9.3. in the code viewer
OBC Div. B 7.4.9.5. Offset in Leaders
(1)No change in the nominal pipe size of a leader with a nominally horizontal offset is required if the offset
(a)is located immediately under the roof,
(b)is not more than 6 m long, and
(c)has a slope of not less than 1 in 50.
(2)If the horizontal offset is more than 6 m long, the leader shall conform to Table 7.4.10.9.
Open OBC Div. B 7.4.9.5. in the code viewer
OBC Div. B 7.4.10.1. Total Load on a Pipe
(1)The hydraulic load on a pipe is the total load from
(a)every fixture that is connected to the system upstream of the pipe,
(b)every fixture for which provision is made for future connection upstream of the pipe, and
(c)all roofs and paved surfaces that drain into the system upstream of the pipe.
Open OBC Div. B 7.4.10.1. in the code viewer

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OBC Div. B Table 7.4.9.3. Minimum Permitted Size of Fixture Outlet Pipe and Hydraulic Loads for Fixtures[1]
Table 7.4.9.3. — Minimum Permitted Size of Fixture Outlet Pipe and Hydraulic Loads for Fixtures[1] Forming Part of Sentences 7.4.9.3.(1) and 7.4.10.2.(1) Fixture | Minimum Nominal Pipe Size of Fixture Outlet Pipe, NPS | Hydraulic Load, fixture units Autopsy table | 1½ | 2 Bathroom group (a) with flush tank | N/A | 6 Bathroom group (b) with direct flush valve | N/A | 8 Bathtub (with or without shower) | 1½ | 1½ Bath: foot, sitz or slab | 1½ | 1½ Beer cabinet | 1½ | 1½ Bidet | 1¼ | 1 Chinese range | 1½ | 3 Clothes washer (a) domestic[1] | N/A | 1½ with NPS 2 trap Clothes washer (b) commercial | N/A | 2 with NPS 2 trap Cup sinks | 1¼ | ½ Dental unit or cuspidor | 1¼ | 1 Dishwasher (a) domestic type | 1½ | 1 (no load when connected to garbage grinder or domestic sink) Dishwasher (b) commercial type | 2 | 3 Drinking fountain | 1¼ | ½ Fish tank or tray | 1½ | 1½ Floor drain[2] | 2 | 2 with NPS 2 trap 3 with NPS 3 trap Garbage grinder, commercial type | 2 | 3 Icebox | 1¼ | 1 Laundry tray (a) single or double units or 2 single units with common trap | 1½ | 1½ Laundry tray (b) compartments | 1½ | 2 Lavatory (a) barber or beauty parlor | 1½ | 1½ Lavatory (b) dental | 1¼ | 1 Lavatory (c) domestic type single, or 2 single with common trap | 1¼ | 1 with NPS 1¼ trap 1½ with NPS 1½ trap Lavatory (d) multiple or industrial type | 1½ | According to Table 7.4.10.2. Macerating toilet system | ¾ | 4 Potato peeler | 2 | 3 Shower drain Total volume of discharge from all shower heads and body sprays: (a) from 1 head | 1½ | 1½ Shower drain Total volume of discharge from all shower heads and body sprays: (b) from 2 or 3 heads | 2 | 3 Shower drain Total volume of discharge from all shower heads and body sprays: (c) from 4 to 6 heads | 3 | 6 Sink (a) domestic and other small types with or without garbage grinders, single, double or 2 single with a common trap | 1½ | 1½ Sink (b) other sinks | 1½ | 1½ with NPS 1½ trap 2 with NPS 2 trap 3 with NPS 3 trap Urinal (a) pedestal, siphon jet or blowout type | 2 | 4 Urinal (b) stall, washout type | 2 | 2 Urinal (c) wall (i) washout type | 1½ | 1½ Urinal (c) wall (ii) other types | 2 | 3 Water closet (a) with flush tank | 3 | 4 Water closet (b) with direct flush valve | 3 | 6 Notes to Table 7.4.9.3.: (1) See Note A-Table 7.4.9.3. (2) No hydraulic load for emergency floor drains.
Open OBC Div. B Table 7.4.9.3. in the code viewer
OBC Div. B Table 7.4.10.2. Permitted Hydraulic Load from a Fixture Based on Size of Trap
Table 7.4.10.2. — Permitted Hydraulic Load from a Fixture Based on Size of Trap Forming Part of Sentence 7.4.10.2.(2) Nominal Pipe Size, NPS | Hydraulic Load fixture units 1¼ | 1 1½ | 2 2 | 3 2½ | 4 3 | 5 4 | 6
Open OBC Div. B Table 7.4.10.2. in the code viewer
OBC Div. B 7.4.10.3. Hydraulic Loads from Fixtures with a Continuous Flow
(1)Except as provided in Sentence (2), the hydraulic load from a fixture that produces a continuous flow, such as a pump or an air-conditioning fixture, is 31.7 fixture units for each litre per second of flow.
(2)Where a fixture or equipment that produces a continuous or semi-continuous flow drains to a combined sewer or to a storm sewer, the hydraulic load from the fixture is 900 L for each litre per second of flow.
Open OBC Div. B 7.4.10.3. in the code viewer
OBC Div. B Table 7.4.10.12. Maximum Permitted Hydraulic Load from Fixtures with a Semi-continuous Flow —
Table 7.4.10.12. Maximum Permitted Hydraulic Load from Fixtures with a Semi-continuous Flow — Forming Part of Sentence 7.4.10.12.(1) Nominal Pipe Size of Trap, NPS | Flow, L/s | Hydraulic Load, fixture units 1½ | 0.000 - 0.090 | 3 2 | 0.091 - 0.190 | 6 3 | 0.191 - 0.850 | 27 4 | 0.851 - 5.700 | 180
Open OBC Div. B Table 7.4.10.12. in the code viewer
OBC Div. B 7.4.10.4. Hydraulic Loads from Roofs or Paved Surfaces
(1)Except as provided in Sentence (2), the hydraulic load in litres from a roof or paved surface is the maximum 15 min rainfall determined in conformance with MMAH Supplementary Standard SB-1, "Climatic and Seismic Data," multiplied by the sum of
(a)the area in square metres of the horizontal projection of the surface drained, and
(b)one-half the area in square metres of the largest adjoining vertical surface.
(2)Flow control roof drains may be installed, provided
(a)the maximum drain down time does not exceed 24 h,
(b)the roof structure is designed to carry the load of the stored water,
(c)one or more scuppers are installed not more than 30 m apart along the perimeter of the building so that
(i)up to 200% of the 15-minute rainfall intensity can be handled, and
(ii)the maximum depth of controlled water is limited to 150 mm,
(d)they are located not more than 15 m from the edge of the roof and not more than 30 m from adjacent drains, and
(e)there is at least one drain for each 900 m².
(3)Reserved.
(4)Where the height of the parapet is more than 150 mm or exceeds the height of the adjacent wall flashing,
(a)emergency roof overflows or scuppers described in Clause (2)(c) shall be provided, and
(b)there shall be a minimum of 2 roof drains.
Open OBC Div. B 7.4.10.4. in the code viewer
OBC Div. B 7.4.10.5. Conversion of Fixture Units to Litres and Gal/min
(1)Except as provided in Sentence 7.4.10.3.(2), where the hydraulic load is to be expressed in litres, fixture units shall be converted as follows:
(a)when the number of fixture units is 260 or fewer, the load is 2,360 L, and
(b)when the number of fixture units exceeds 260, the load is 9.1 L for each fixture unit.
(2)Where the hydraulic load is to be expressed in gal/min, fixture units shall be converted in accordance with Table 7.4.10.5.
Open OBC Div. B 7.4.10.5. in the code viewer
OBC Div. B Table 7.4.10.6-A. Maximum Permitted Hydraulic Load Drained to a Stack
Table 7.4.10.6.-A Maximum Permitted Hydraulic Load Drained to a Stack Forming Part of Sentences 7.4.10.6.(1) and 7.5.7.3.(2) and Table 7.5.8.4. Nominal Pipe Size of Stack, NPS | Maximum Hydraulic Load, fixture units | Maximum Fixture Units Drained from any 1 Storey 1¼ | 2 | 2 1½ | 8 | 2 2 | 24 | 6 3 | 102 | 18 4 | 540 | 100 5 | 1,400 | 250 6 | 2,900 | 500 8 | 7,600 | 830 10 | 15,000 | 2,700 12 | 26,000 | 4,680 15 | 50,000 | 9,000
Open OBC Div. B Table 7.4.10.6-A. in the code viewer
OBC Div. B Table 7.4.10.6-B. Maximum Permitted Hydraulic Load Drained to a Branch
Table 7.4.10.6.-B — Maximum Permitted Hydraulic Load Drained to a Branch Forming Part of Sentences 7.4.10.6.(2), 7.4.10.7.(1) and 7.5.7.3.(2) Nominal Pipe Size of Branch, NPS | Maximum Hydraulic Load, fixture units 1¼ | 2 1½ | 3 2 | 6 3 | 27 4 | 180 5 | 390 6 | 700 8 | 1,600 10 | 2,500 12 | 3,900
Open OBC Div. B Table 7.4.10.6-B. in the code viewer
OBC Div. B Table 7.4.10.6-C. Maximum Hydraulic Load, fixture units[2]
Table 7.4.10.6.-C[1] — Maximum Hydraulic Load, fixture units[2] Forming Part of Sentence 7.4.10.6.(2) and Article 7.4.10.8. Nominal Pipe Size of Drain or Sewer, NPS | Slope: 1 in 400 | Slope: 1 in 200 | Slope: 1 in 133 | Slope: 1 in 100 | Slope: 1 in 50 | Slope: 1 in 25 3 | N/A | N/A | N/A | N/A | 27 | 36 4 | N/A | N/A | N/A | 180 | 240 | 300 5 | N/A | N/A | 380 | 390 | 480 | 670 6 | N/A | N/A | 600 | 700 | 840 | 1,300 8 | N/A | 1,400 | 1,500 | 1,600 | 2,250 | 3,370 10 | N/A | 2,500 | 2,700 | 3,000 | 4,500 | 6,500 12 | 2,240 | 3,900 | 4,500 | 5,400 | 8,300 | 13,000 15 | 4,800 | 7,000 | 9,300 | 10,400 | 16,300 | 22,500 Notes to Table 7.4.10.6.-C: (1) See Note A-Table 7.4.10.6.-C. (2) Slope is the ratio of rise to run, in whatever measurement units are chosen.
Open OBC Div. B Table 7.4.10.6-C. in the code viewer
OBC Div. B Table 7.4.10.9. Maximum Permitted Hydraulic Load, L[1]
Table 7.4.10.9. — Maximum Permitted Hydraulic Load, L[1] Forming Part of Sentence 7.4.9.5.(2) and Article 7.4.10.9. Nominal Pipe Size of Drain or Sewer, NPS | Slope: 1 in 400 | Slope: 1 in 200 | Slope: 1 in 133 | Slope: 1 in 100 | Slope: 1 in 68 | Slope: 1 in 50 | Slope: 1 in 25 3 | N/A | N/A | N/A | N/A | N/A | 2,770 | 3,910 4 | N/A | N/A | N/A | 4,220 | 5,160 | 5,970 | 8,430 5 | N/A | N/A | 6,760 | 7,650 | 9,350 | 10,800 | 15,300 6 | N/A | N/A | 10,700 | 12,400 | 15,200 | 17,600 | 24,900 8 | N/A | 18,900 | 23,200 | 26,700 | 32,800 | 37,800 | 53,600 10 | N/A | 34,300 | 41,900 | 48,500 | 59,400 | 68,600 | 97,000 12 | 37,400 | 55,900 | 68,300 | 78,700 | 96,500 | 112,000 | 158,000 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.
Open OBC Div. B Table 7.4.10.9. in the code viewer
OBC Div. B Table 7.4.10.10. Maximum Hydraulic Load, L
Table 7.4.10.10. — Maximum Hydraulic Load, L Forming Part of Article 7.4.10.10. Nominal Pipe Size of Gutter, NPS | Area of Gutter, cm² | Slope: 1 in 200 | Slope: 1 in 100 | Slope: 1 in 50 | Slope: 1 in 25 3 | 22.8 | 406 | 559 | 812 | 1,140 4 | 40.5 | 838 | 1,190 | 1,700 | 2,410 5 | 63.3 | 1,470 | 2,080 | 2,950 | 4,170 6 | 91.2 | 2,260 | 3,200 | 4,520 | 6,530 7 | 124.1 | 3,250 | 4,600 | 6,500 | 9,190 8 | 162.1 | 4,700 | 6,600 | 9,400 | 13,200 10 | 253.4 | 8,480 | 12,000 | 17,000 | 23,600
Open OBC Div. B Table 7.4.10.10. in the code viewer
OBC Div. B Table 7.4.10.11. Maximum Permitted Hydraulic Load Drained to a Leader
Table 7.4.10.11. — Maximum Permitted Hydraulic Load Drained to a Leader Forming Part of Sentence 7.4.10.11.(1) Circular Leader: Nominal Pipe Size of Leader , NPS | Circular Leader: Maximum Hydraulic Load, L | Non-Circular Leader: Area of Leader, cm² | Non-Circular Leader: Maximum Hydraulic Load, L 2 | 1,700 | 20.3 | 1,520 2½ | 3,070 | 31.6 | 2,770 3 | 5,000 | 45.6 | 4,500 4 | 10,800 | 81.1 | 9,700 5 | 19,500 | 126.6 | 17,600 6 | 31,800 | 182.4 | 28,700 8 | 68,300 | 324.3 | 61,500
Open OBC Div. B Table 7.4.10.11. in the code viewer
OBC Div. B 7.4.10.6. Hydraulic Loads to Soil or Waste Pipes
(1)Except as provided in Sentence (2), the hydraulic load that is drained to every stack shall conform to Table 7.4.10.6.-A.
(2)Where the nominally horizontal offset in a stack is 1.5 m or more, the hydraulic load that is served by it shall conform to Table 7.4.10.6.-B or Table 7.4.10.6.-C, whichever is the less restrictive.
(3)Vertical sanitary drainage pipe shall be designed to carry no more than 29% of its full capacity.
Open OBC Div. B 7.4.10.6. in the code viewer
OBC Div. B 7.4.10.8. Hydraulic Loads on Sanitary Building Drains or Sewers
(1)Except as permitted by Article 7.4.10.7., the hydraulic load that is drained to a sanitary building drain or a sanitary building sewer shall conform to Table 7.4.10.6.-C.
(2)Horizontal sanitary drainage pipe shall be designed to carry no more than 65% of its full capacity.
Open OBC Div. B 7.4.10.8. in the code viewer