I am adding a pedestal sing in a new bathroom I adding to my home. I was wondering if a self-tapping valve is an acceptable way of connectong to the existing water supply. I have 1/2" copper lines in the wall directly behind where I am placing the sink. Any suggestions would be appreciated!
You're not going to find a piercing valve suitably sized to provide the volume necessary for a ped sink.
In a word, piercing valves 'suck'. They generally always begin to leak, sooner or later. There is no real reason, other than your own lack of skill or confidence, that you need to hot tap a line inside a dwelling.