Ideal Setup For HVAC Installation?

KesslerDweller

We are designing a couple new houses that are geared towards energy efficiency (particularing cooling in Texas) and wanted to ask some questions. These are two story, 3,000 square foot houses.

Are 18" open web trusses (between the first and second floor) two small for duct work and return air? We have used 18 inch trusses in past and it seems the AC guys end up choking some of the lines more than I would like. I don't know if they are inadequate or just like to whine about it. Obviously 24 inch trusses would be better, but they are more expensive.

What about I-joists?

Is insulated ductboard better than flex duct?
http://www.owenscorning.com/comminsu...sp?product=271

Thanks!