Waste Traps and Waste Pipes
Building Regulations require that all points of discharge into a drainage system should be fitted with a trap (e.g. a water seal trap) to prevent foul air from the system entering the building. Under working and test conditions traps should retain a minimum seal of 25mm of water or equivalent.
Installation Requirements
All Traps, Waste Pipe, Waste Fittings and Soil Fittings When Installed in Buildings should be installed in compliance With:
1) The Building Regulations 2000 (as amended) England and Wales.
2) The Building Standards (Scotland) Regulations 1990 (as amended).
3) The Building regulations (Northern Ireland) 2000.
Alternatively the relevant recommendations of BS EN 12056 should be followed.
All traps should be accessible and provided with an adequate facility for cleansing, for example, traps that are capable of being readily removed or dismantled. In general a trap which is not an integral part of an appliance should be attached to, and be immediately beneath, its outlet. However, traps that are not connected to the appliance should be as close as possible. There should be no more than one trap on the discharge pipework from any appliance.
Types of Trap
Bottle Traps
 This type of trap has a division between the inlet and outlet legs formed by a dip tube or vane within the body of the trap, with the lower part of the trap being removable for access. Bottle traps should only be used with wash basins.
Tubular Traps
 Tubular Traps can be supplied in either "P" or "S" configuration and there are many variations and modifications to make them particularly suitable for any application.
Trap Seals
Traps with outlets for pipes up to and including DN50 should have a minimum water seal of 50 mm on baths and showers, provided they are fitted with flush-grated wastes without plugs on spray-tap basins; 75 mm trap seals should be used with all other appliances.
Traps with outlets for pipes over DN 50 should have a minimum water seal of 50 mm.
Traps used on appliances with flat bottoms (trailing waste discharge) and discharging to a gully with a grating may have a reduced water seal of not less than 38 mm.
Table 6 - Limitations for Unventilated Branch-Discharge-Pipes, System III
|
Appliance |
Diameter (DN) |
Min Trap Seal Depth (mm) |
Max Length (L) of Pipe from Trap Outlet to Stack (m) |
Pipe Gradient (%) |
Max Number of Bends (No) |
Max Drop (m) |
|
Washbasin, Bidet (30mm diameter trap) |
30 |
75 |
1.7 |
2.2(1) |
0 |
0 |
|
Washbasin, Bidet (30mm diameter trap) |
30 |
75 |
1,1 |
4.4(1) |
0 |
0 |
|
Washbasin, Bidet (30mm diameter trap) |
30 |
75 |
0.7 |
8.7(1) |
0 |
0 |
|
Washbasin, Bidet (30mm diameter trap) |
40 |
75 |
3.0 |
1.8 to 4.4 |
2 |
0 |
|
Shower, Bath |
40 |
50 |
No Limit(2) |
1.8 to 9.0 |
No Limit |
1.5 |
|
Bowl Urinal |
40 |
75 |
3.0(3) |
1.8 to 9.0 |
No Limit(4) |
1.5 |
|
Trough Urinal |
50 |
75 |
3.0(3) |
1.8 to 9.0 |
No Limit(4) |
1.5 |
|
Slab Urinal |
60 |
50 |
3.0(3) |
1.8 to 9.0 |
No Limit(4) |
1.5 |
|
Kitchen Sink (40mm diameter trap) |
40 |
75 |
No Limit(2) |
1.8 to 9.0 |
No Limit |
1.5 |
|
Household Dishwasher or Washing Machine |
40 |
75 |
3.0 |
1.8 to 4.4 |
No Limit |
1.5 |
|
WC With Outlet Up To 80mm(6) |
75 |
50 |
No Limit |
1.8 Min |
No Limit(4) |
1.5 |
|
WC With Outlet Greater Than 80mm(6) |
100 |
50 |
No Limit |
1.8 Min |
No Limit(4) |
1.5 |
|
Food Waste Disposal(7) |
40 Min |
75(8) |
3.0(3) |
13.5 Min |
No Limit(4) |
1.5 |
|
Sanitary Towel Disposal Unit |
40 Min |
75(8) |
3.0(3) |
5.4 Min |
No Limit(4) |
1.5 |
|
Floor Drain |
50 |
50 |
No Limit(3) |
1.8 Min |
No Limit |
1.5 |
|
Floor Drain |
70 |
50 |
No Limit(3) |
1.8 Min |
No Limit |
1.5 |
|
Floor Drain |
100 |
50 |
No Limit(3) |
1.8 Min |
No Limit |
1.5 |
|
4 Basins |
50 |
75 |
4.0 |
1.8 to 4.4 |
0 |
0 |
|
Bowl Urinals(8) |
50 |
75 |
No Limit(3) |
1.8 to 9.0 |
No Limit(4) |
1.5 |
|
Maximum of 8 WCs(6) |
100 |
50 |
15.0 |
0.9 to 9.0 |
2 |
1.5 |
|
Up to 5 Spray Tap Basins(9) |
30 Max |
50 |
4.5(3) |
1.8 to 4.4 |
No Limit(4) |
0 |
Notes
- Steeper gradient permitted if pipe is less than maximum permitted length.
- If length is greater than 3 m noisy discharge may result with an increased risk of blockage.
- Should be as short as possible to limit problems with deposition.
- Sharp throated bend should be avoided.
- For slab urinal for up to 7 persons. Longer slabs to have more than one outlet.
- Swept - entry branches serving WCs.
- Includes small potato-peeling machines.
- Tubular not bottle or resealing traps.
- Spray tap basin shall have flush-grated wastes without plugs.
Extract from BS EN 12056-2:2000 Gravity drainage systems inside buildings
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