Ecotect is a not an addon to any program. It was created by some university in England ( i think so) and i find it nice for sun calculation. I worked on it when doing my master degree.
But if you want to work on Ecotect, you have to do the model from the beginning regarding the zoning of the building.
cheers
The BIMster @ AllesWirdGut
Currently: Archicad 26
User since Archicad 6.5 (2001)