Layout Query

new user and liking the software a lot, using it to set music for a 4pt male Voice choir.

I now have a song with a unison verse (so only need one stave) and then a 4-part chorus (needs two staves).
I can't work out how to switch from 1stave to 2.
When I create the new layout, I can get either 2 staves or 1 stave but don't have an option to start with 1 stave and then add another stave.

I can't be the first to meet this issue so what do I have to do?

Suggestions welcomed as always.