Existing fixture upgrades

You'll need to us the baseline rates from the LEED Ref. Guide. Sadly no extra credit for replacing water hogs. (Although if you get the whole existing building (assuming it's a pretty big existing building) to retrofit all the restrooms (beyond the ones the addition occupants will use), you could potentially get extra credit if it's enough other restrooms... But again the baseline would be from the LEED Ref. Guide...) BTW, just remember that older drain lines don't necessarily slope as much as they should so make sure you have some water flowing down those pipes (be it from the final urinal farthest from the drain/main having flush as opposed to waterless or some water in all, etc...)