Drainage Fixtures - Unit Loads and Sanitary Piping
Maximum Drainage Fixture Unit - DFU - loads for sanitary piping
The relationship between volume flow and fixture units is not constant, but varies with the number of fixture units. A Fixture Unit is not a flow rate unit but a design factor based on the rate of discharge, time of operation and frequency of use of a fixture. A fixture unit is equal to one cubic foot of water drained in an 1 1/4 pipe over one minute (≈ 7.48 US gpm, ≈ 0.47 l/s).
Maximum Drainage Fixture Units (DFU) in Stacks and Horizontal Fixture Branches
Maximum Drainage Fixture Units (DFU) | |||||
---|---|---|---|---|---|
Pipe Size | Horizontal fixture branch | Stacks3) less than three stories in height | Stacks more than three stories high | ||
NPS (inches) | DN (mm) | ||||
Total for stack | Total for one story | ||||
1 1/20) | 40 | 3 | 4 | 8 | 2 |
20) | 50 | 6 | 10 | 24 | 6 |
2 1/20) | 65 | 12 | 20 | 42 | 9 |
3 | 80 | 201) | 481) | 722) | 201) |
4 | 100 | 160 | 240 | 500 | 90 |
5 | 125 | 360 | 540 | 1100 | 200 |
6 | 150 | 620 | 960 | 1900 | 350 |
0) No water closet permitted
1) Maximum two water closets
2) Maximum six water closets
3) Stacks - vertical runs of plumbing waste or drainage lines
Maximum Drainage Fixture Units (DFU) in Building Drains and Building Drain Branches from Stacks
Maximum Drainage Fixture Units (DFU) | |||
---|---|---|---|
Pipe Size | Slope (in/ft (cm/m)) | ||
NPS (inches) | DN (mm) | ||
1/4 (2.1) | 1/2 (4.2) | ||
20) | 50 | 21 | 26 |
2 1/20) | 65 | 24 | 31 |
3 | 80 | 421) | 501) |
4 | 100 | 216 | 250 |
5 | 125 | 480 | 575 |
6 | 150 | 840 | 1000 |
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