Shower waste - what size pipe?

[Ar484]

Hi, I have a new shower tray to install that has come with a shower waste trap with 40mm output. The waste needs to run around 3.5m to 4m before connecting to vertical soil stack. I understand building regs require 50mm pipe to be used for this length of run? Do I therefore need a new trap with 50mm output, connect the 40mm pipe to 50mm at first opportunity or something else?
Thanks!

 

[snowhead]

40mm trap and waste from the shower then change up to 50mm at the earliest most convenient point.

 

[Ric2013]

Hi, I have a new shower tray to install that has come with a shower waste trap with 40mm output. The waste needs to run around 3.5m to 4m before connecting to vertical soil stack. I understand building regs require 50mm pipe to be used for this length of run? Do I therefore need a new trap with 50mm output, connect the 40mm pipe to 50mm at first opportunity or something else?
Thanks!

While I agree with Snowhead, don't get too hung up on the dimensions in ADH. What you quote is the Approved Document for Part H. Approved Documents are merely guides as to how to satisfy the requirements of the building regulations itself. The UK is not like the USA or Zimbabwe which both have specific "codes" which MUST be followed.

If you end up with (to make a point) a 4.1m run in 50mm or a 3.1m run in 40mm and it doesn't block or restrict flow, self siphon, or induce siphonage, then it's fine. Obviously there is no harm in oversizing. What I would be more concerned about is good practice in making the joints, proper pipe deburring, use of swept bends, and consideration for clearing of possible blockages.

It is encouraging to see you asking such questions, however.