Drainage Pipes
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RIGID PIPES
Minimum depth under roads 0.7m and 0.4m under fields and gardens. Maximum depth: 7m without additional protection.
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FLEXIBLE PIPES
Minimum depth under roads 0.9m and 0.6m under fields and gardens. Maximum depth: 10m without additional support |
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PIPES THROUGH WALLS
Arch or lintel over opening to give 50mm space all round the pipe. |
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Short length of pipe bedded in wall adjacent
rocker pipes of max length
600mm with flexible joints.
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TRENCHES NEAR BUILDINGS
Where A is less than 1m concrete fill trench to this level. |
Where A is 1m or more concrete fill trench to this level.
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KEY
Selected fill, free from stones larger than
40mm and lumps of clay over 100mm.
Selected backfill free from stones larger
than 40mm.
Granular material. |
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STRUCTURE NEAR PUBLIC SEWERS
R = Radius of pipe
D = Depth
C = Centre line of pipe
W = minimum of 3 metres from edge of foundation to edge of sewer trench.
If line A strikes about bottom of sewer trench then:-
1. W + R to be increased or
2. D to be increased.
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FOUL DRAINAGE
Rigid Pipe
Flexible Pipe
Vitrified clay
uPVC
Concrete
Cast Iron
A drain carrying waste water only should have a diameter of at least 75mm and a drain carrying soil water a diameter of 100mm.
GRADIENT
The traditional rule of thumb of 1:40 for a 100mm drain and 1:60 for a 150mm drain remains good practice - however, with careful laying a 100mm pipe with at least one WC connected can have a gradient of 1:80 and a 150mm with 5 WCs connected can have a minimum gradient of 1:150.
INSPECTION CHAMBERS (Man Holes)
Required at:• on or near head of drain• at a bend or change of gradient• at a change of pipe size• at a junction (unless each run can be cleared from an access point)• to subdivide long runs
MINIMUM INTERNAL DIMENSIONS
| Depth to invert |
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| 0.6m or less |
190mm dia |
| 1m or less |
450mm x 450mm |
| Greater than 1m |
1200mm x 750mm |
TESTING
Drains should be capable of withstanding a suitable water test or air test after backfilling.
RAINWATER DRAINAGE
| METHOD OF CALCULATING THE AREA DRAINED |
| Type of Surface |
Design Area |
| 1. Flat Roof |
Plan Area |
| 2. Pitched Roof at 30% |
Plan area x 1.15 |
| Pitched Roof at 45% |
Plan area x 1.40 |
| Pitched Roof at 60% |
Plan area x 2.00 |
| 3. Pitched Roof over 70% |
Elevation area x 0.6 |
RAINWATER GUTTERS
| Max Design |
Gutter Size |
Outlet |
Flow/Capacity |
| Area m2 |
mm dia |
mm dia |
LTR/sec |
| 18.0 |
75 |
50 |
0.38 |
| 37.0 |
100 |
63 |
0.78 |
| 53.0 |
115 |
63 |
1.11 |
| 65.0 |
125 |
75 |
1.37 |
| 103.0 |
150 |
89 |
2.16 |
SOAKAWAYS
CAPACITY:
Equal to a 12mm rainfall over the drained area.
SITING:
At least 4.5m from any building.
CONSTRUCTION:
A pit filled with hardcore and capped with a thin layer of concrete or polythene sheet. OR a hollow pit lined with brick or concrete rings with a top containing a manhole cover.
Please check with your local building control department before using information contained in this page to ensure that they comply with your local building codes.