Hi Lee,
Although we have residential and commercial work, they are just descriptions. A window is a window is a window, and if you can clean it - it's fair game.
Move onto commercial work by all means, but don't think of dropping your residential stuff - the cashflow is normally much better and commercial jobs require invoices before they'll process payment.
If you're looking for other types of work, have you thought of a pressure washer for drives and cladding? That might be worth considering.
All the best for whichever way the business goes.