Hepworth HDPE Drainage

Peripheral requirements for removal of waste water

Peripheral requirements for removal of waste water

3.6 Ventilation pipes The ventilation pipe serves to admit and vent air to and from the discharge system. The diameter should be the same as that of the stack, ignoring any reduced section of stack. The diameter may be reduced by one step if all the following conditions are met: - total length of the stack is less than 20 metres; - length of the ventilation pipe is less than 10 metres; - total length of the ventilation pipe including the reduced stack section is less than 10 metres: - there are no more than 4 bends of 90°or 6 bends of 45°; - the reduction does not occur in the combined section of a ventilation pipe. Ventilation pipes may be horizontal. Ventilation pipes for several stacks may be combined into a single roof penetration provided: - the diameter is at least that of the largest stack; - the combined section is not reduced; - no more than 10 stacks are combined.

Particularly where there are several horizontal sections in the stack a balancing line must be provided (illustration 3.15). Each vertical section must be connected to the corresponding vertical section of the stack with a downward-facing 45° T-piece. The diameter of the balan- cing line must be at least 0.8 times the largest diameter in the relevant stack section. Connection-free zones are also applicable here. 3.4.4 Stack diameter This is calculated by taking the sum of the baseline discharges and the largest baseline discharge at the foot of the stack, using Illustration 4.2. Where the stack is connected with horizontal sec- tions as in illustration 2.5, 3.13 and 3.15, then the diameter must be established separately for each section. A reduction by one step in size is permissible for the upper part of the stack, provided the total length of the discharge pipe plus the reduced stack is no more than 10 metres. The diameter of the reduced stack section must of course remain at least as large as that of the connection above. 3.5 Underground pipes For underground pipes taking domestic waste water only, all the criteria apply as set down for stacks. Connecting pipes and stacks must be connected to underground pipes via a side connection, an oblique connection or a top connec- tion at 45° (illustrations 3.5, 3.6 and 3.7).

Illus. 3.13 Transition between stack /

Illus. 3.14 Connection in a connection-free zone.

Illus. 3.15 Example of a balancing line. See also illus. 2.4 and 2.5.

horizontal pipe and connection- free zones.

3.7 Roof penetrations The vent pipe is taken through the roof. A cap is usually fitted to the pipe end. Stench from the waste system may not cause nuisance. A number of require- ments and conditions are set down to achieve this: The outlet area for the outgoing flow must have at least the same surface area as the cross-sectional area of the discharge pipe. The vent pipe must protrude suffi- ciently above the roof (to take account of snow among other things). The vent pipe must not penetrate a wall. The vent pipe opening must be at least 1 metre above the highest point of any air opening (door, roof-light, ventilation opening). The vent pipe must be at least 8 metres from any: - roof terrace or other external space; - air opening (door, roof-light, ventilation opening) in the wall if the roof joins a rising wall.

facility should in any event be provided with an approval mark. Grey and also black water may be so purified that it can be used as a domestic water source. Contact the local authority for more information about the possibilities and obligations.

The foregoing will explain why ventilated roof tiles are strongly discouraged. In the case of buildings higher than 20 metres, or adjacent to buildings above that height it is possible that wind effects will create overpressure or underpressure around the vent opening. In that case the vent must be placed as far as possible from the roof perimeter or adjacent high wall.

Illus. 3.11 Separations and angles for connections to stacks.

3.8 Discharge of waste water

Grey or black waste water may not be discharged into the surface water or infiltrated into the ground without purification. In most cases the waste water will be led off via the local authority sewer. In certain circumstances in outlying areas where no sewer is available it may be permitted to purify the water to the extent that it can be discharged. Depending on the sensitivity of the area a simple or more advanced individual water treatment facility may be required. Such a

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Illus. 3.12 Angled sections in a stack.

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