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ABOVE GROUND DISCHARGE SYSTEMS

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					                                                                                  UNIT 7
                                                ABOVE GROUND
                                                   DISCHARGE
                                                     SYSTEMS
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                                          Summary
                                          Above ground discharge systems (AGDS) are essential to ensure that
                                          we are able to keep outselves and our household environment clean
                                          and hygienic. In the unit on AGDS we will look at:
                                          • Sanitary systems
                                          • Sanitary appliances
                                          • Sanitary pipework and fittings, and the various appliances on the
                                             market, and how to install them
                                          • How to test and maintain systems
                                          • Rain water drainage – that is guttering and fall pipe systems
                                          • De-commissioning systems.




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         262   Plumbing




               Sanitary systems                  Introduction
                                                 The majority of systems in new domestic dwelling installations
                                                 are known as primary ventilated stacks. You may still hear this
                                                 referred to as ‘single stack on site’.
                                                 Plumbers are involved in maintenance work and some of the
                                                 earlier above ground discharge systems you may still come across
                                                 were loosely classified as ‘two pipe’. This is where the pipework
                                                 from the WC was separate from that of the washbasin, bath
                                                 and sink. The waste water only joined forces once it entered
                                                 the drain.
                                                 Today, all pipework systems used on domestic dwellings are based
                                                 on an one-pipe system with four variations on the theme.
                                                 The design and installation of systems must comply with Building
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                                                    Regulations Part H1 2002, which supersedes the 1992 edition. As
                                                 well as the guidance given in H1, BS 8000 - 13; Workmanship on
                                                 building sites Part 13: Code of practice for above ground drainage
                                                 and sanitary appliances provides additional information on good
                                                 practice related to AGDS.
                                                 BS EN 12056 provides additional guidance on such a pipework
                                                 system design including waste pipe connections, trap seal and
                                                 ventilation of system pipework.
                                                 H1 2002 can be downloaded from the website called the Planning
UNIT 7




                                                 Portal, www.planningportal.gov.uk. If you do not have internet
                                                 access, their address is:
                                                 Communities and Local Government
                                                 Eland House
                                                 Bressenden Place
                                                 London
                                                 SW1E 5DU
                                                 Tel: 020 7944 4400
                                                 BS 8000 Part 13 and BS EN 12056 can be obtained from BSI on
                                                 020 8996 9001, but there will be a cost, alternatively you can try
                                                 the library, but your college or centre should have a copy.

                                                 Types of systems
                                                 There are four types of systems in use today and these are:
                                                   ●   Primary ventilated stack systems
                                                   ●   Stub stack and systems using air-admittance valves




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                                                                                      Above ground discharge systems    263




                                             ●   Ventilated discharge branch systems
        Key point                            ●   Secondary modified ventilated stack systems.
        H1 lays down a number of ‘rules’
        that you need to remember
                                           All these systems can be installed either inside or outside the
        which relate to any system         building.
        design.
        The H1 rules are based around:
        ●     The size of the discharge    Primary ventilated stack system
              pipes                          You are most likely to install this type of system in the majority of
          ● The maximum length of the
                                             domestic dwelling situations.
              discharge pipes
          ● The gradient of the              Figure 7.1 is an example of a primary ventilated stack, which
              discharge pipes                complies with H1.
          ● The location of branch
              connections                    There are limitations to the minimum pipe sizes, maximum
          ● The connection of the soil       lengths of the branch connections and their gradients.
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              pipe to the drain.
                                           These can be summarised as shown in Table 7.1
                                           In this system you should have the appliances grouped closely
                                           together. There is some flexibility, however. For example, if you
                                           did install a shower with a 50 mm waste it could be located up to
                                           4 m away from the stack as opposed to 3 m if using 40 mm pipe.
                                           The size of the branch pipes should always be at least the same
                                           diameter as the trap.




                                                                                                                              UNIT 7
                                                                                            32 mm
                                                                                            diameter
                                                                           40 mm
                                                                           diameter
                                                                                                WB     WC   40 mm
                                                                  Bath
                                                                                                            diameter
                                                                               Bidet




                                                        50 mm parallel junction                 32 mm
                                                            to avoid crossflow                  diameter

                                                                                                WB     WC
                                                                              Sink
                                             Washing Machine
                                              (or dishwasher)

                                                                40 mm                           450 mm      75–100 mm
                                                                diameter                        min         diameter


      Figure 7.1    Primary ventilated                                            Long radius
      stack                                                                       bend




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         264   Plumbing




                                                   Table 7.1

                                                                 Pipe size    Max Length            Slope
                                                                 (mm)         (m)
                                                    Basin         32          1.7                   18–80 mm fall per m run
                                                    Bath          40          3.0                   19–90
                                                    *Shower       50          4.0                   18–90
                                                    WC           100          6.0                   18 h mm/m min



                                                   Branch connections
                                                    The location of a branch pipe in a stack should not cause cross flow
               Key point                            into another branch pipe (cross flow happens when two branches
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                The primary ventilated stack        are located opposite to each other). Cross flow can be prevented by
                system is popular because it        working on the following details, as shown in Figure 7.2.
               costs less in materials and
               installation time, as it does not   You might find on some installations that it is easier to run the
               need a separate ventilating pipe    kitchen sink waste pipe into a gulley rather than pipe to the stack.
               like other one-pipe systems.        This is allowed as long as the pipe end finishes between the grat-
               This is good for the plumber        ing or sealing plate and the top of the water seal. These branch
               and good for the environment        connection principles also apply to the ventilated discharge
               (less material production).         branch and secondary ventilated stack systems mentioned a little
                                                   later.
UNIT 7




                                                                                              45°

                        21
                         2
                     Diameter                                                                                  1     1
                                                                                                            87 2°–67 2 °
                                      250 mm
                                      max



                                                                                          200 mm                   50 mm
                                                                                                                   radius
                         radius not more
                             than 25 mm
                                                                                                                    Permitted
                                                                                                                    connections



                  (a)                                                               (b)
                  Figure 7.2     Branch pipe locations




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