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I am seeking some advice!

I have a commercial property that we are renovating which has a 4inch cast main stack running through it. The lady who's property it is wants 6 ensuites spread over 2 stories each with a toilet, shower and basin installed. Is the one soil stack enough at 4inch or would this need increasing to a 6inch or even 8inch?

The largest horizontal run from the stack is roughly 8m and that with 2 ensuites going into the same one. Is this overloading the main stack/ drain?

Thanks in advance

Building regs part h gives the requirements for stacks.

Get the building control guy in early as they will need to approve and inspect. Ask them what they want to see.