Drainage / Waste routes and plans for extensions and renovations

[OldieNewbie]

With extensions and renovations, who specifies the drainage routes etc? 
 

It would hardly be an architect would it?

 

Or would it be down to the contractor to know. So for example if the architect specified a toilet here and a sink there, it is expected the builder knows what he is doing? 
 

Or would there be drawings for such things?

 

I seen a ground worker on Tik Tok on a large scale site having a drawing. 

[ETC]

Should be a drawing by your agent.

[OldieNewbie]

14 hours ago, ETC said:

Should be a drawing by your agent.

What’s an agent?

[Marvin]

In construction, a site agent will normally be responsible for inspecting construction works as they proceed on behalf of a client, identifying problems with and providing solutions for to ensure project costs are controlled.