Page 570 - The City and Guilds Textbook: Plumbing Book 1 for the Level 3 Apprenticeship (9189), Level 2 Technical Certificate (8202) and Level 2 Diploma (6035)

The City & Guilds Textbook: Plumbing Book 1

32mm
50mm 40mm

To prevent induced siphonage on a multiple appliance installation from a single waste
pipe connected to a primary ventilation system, the waste pipe must increase in size to
50mm as shown before entering the soil stack

p Figure 9.12 Multiple appliance installations

General sanitary pipework requirements

As well as the requirements we have already looked at, sanitary pipework
systems should follow the general rules listed below.
● Where a ventilation stack is installed within 3 m of an opening window, the
stack should be installed at least 900 mm above the window.
● A cage should be fitted to the top of the vent pipe to prevent birds nesting at
the top of the stack. Birds’ nests have the effect of blocking off the air supply
to the stack, causing waste pipes to lose their trap seal.
● A vent cowl should be fitted in exposed or windy positions to prevent
‘wavering out’, where the wind blowing across the top of the stack causes
the trap water to move from side to side, potentially resulting in trap seal
loss by the momentum of the water.
● Access should be provided above the spill-over level of the highest appliance,
to allow for clearing blockages.
● When installing a soil stack for waste pipes only, the size of the stack must
be at least the same size as the largest trap or branch connection to it.

Access cover positioned above the
spill-over level of the highest appliance
900 mm

Less than 3m

p Figure 9.13 The position of a vent stack next an opening window p Figure 9.14 The position of access

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