I had a feeling it might mean adding another G at the top end as a C chord must have a G in it anyway or it is no longer a C chord. Therefore Cadd5 would have two Gs in it not one and the additional one would be the top note (an octave higher than the real G)...

The G is the highest note in a C chord in a pure 3 note standard form in any case so I would personally find this second G to be superfluous (mind you, I play Country/Folk where the rule is KISS). OTOH, on a guitar an Open C chord would have E on the top, followed by C, followed by G. The strictest purest form would be to mute the top two strings and the bottom string and play only the 3rd, 4th and 5th strings - CEG.

So, is this Cadd5 actually a full Open C with G on the top string? I think so. It sounds logical to me but then to go to that amount of trouble with the left hand would imply a full six string strum with the right hand and therefore it should really be Cadd5/E (032013) or Cadd5/G (332013). But all of this is really hypothetical BS - (a)the chord does not officially exist and (b)a full Cadd5 would be physically impossible to finger on one hand on a standard size piano, I should imagine, and hence unlikely to ever appear in a book of chords as most chord nomenclature is focused on piano voicings.

In its simplest form I would plump for the C5 to emphasis_ the G by removing the E.

Ergo => for Cadd5 read C5

Follow That Dream

Sam
Karaoke King

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Turning that corner again - I have to keep following that dream, no matter what