I am currently building a timber frame house in Scotland so Scottish Water regulations.  Can anyone advise how many double check valves I need to fit and where.  I am aware I need (at the incoming mains) an isolator, double check valve and drain point which I have already installed.  I have heard conflicting reports that I need them at every appliance ie dishwasher, washing machine, showers etc.  Others say just at the incomer.  Any one know the definitive answer to the question.  Regards 

No just the one on the incoming.

 

and one on the site stand pipe.

 

And one on the feed to the static caravan.