• Description

Drainage Pipes

 

RIGID PIPES
Minimum depth under roads 0.7m and 0.4m under fields and gardens. Maximum depth: 7m without additional protection.



 

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.

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.

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.

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.

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.