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 |
PIPES THROUGH WALLS
Arch or lintel over opening to give 50mm
space all round the pipe. |
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 |
| | 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.
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