Cj,
You have to at least cover the outer edge at a minimum, the rest is based on how much tolerance for birds your client has.
If these are high rise balcony ledges I'd expect no tolerance due to people and the mess.
Bird barrier and all manufacturers will give you free advice with a quick phone call or email. I typically spread my rows (if multiple are needed) about 3-4" apart for pigeons. That for me is typically close enough together for birds of that size whereas smaller birds can land between less space (sparrows and such).
I'd encourage you to build a relationship with a supplier, they hear and see many scenarios and this advice can save you time, money, frustration and client issues.
You can still do what you like after they advise you and certainly not saying you won't get some thoughts here or from colleagues but a good place to start.
If you want an idea of how many rows sign up for an account with bird barrier it is free and enter in your ledge specs and it will spit out what they recommend that you can at least start from. It's not perfect but a great hel when you are starting to use more products.
Best,
Justin
Last edited by HD_Wildlife; 03/03/15 07:32 PM.