Exposed ductwork? – GreenBuildingAdvisor

I want to build on stem walls with a slab floor.  I’m aware trusses with duct chases can be built, but they have their air sealing issues and don’t address the branch ducts which need to supply conditioned air over windows. Why not build 1′ taller and hang spiral or oval ductwork?  This would also make additions, or in my case, enlarging a one bedroom into a three bedroom via an oversized garage possible for a new owner.  

Thanks