Hello everyone, quick back story. I'm building a home at a estates that's close to a riverbank. So because of potential unstable soil you need a Engineered Raft Foundation. And to cut back on overhead costs we decided to go with a Engineered raft Slab Foundation instead of a dug basement, and then we started looking at Radiant heat to put right in the slab which ended up being to expensive.

So here is my question, we need to go with forced air and we have a Slab foundation. At the current moment we are thinking of putting a open web engineered floor truss on top of the slab so we can run ducting. Is there any other options we could do that would be more cost effective.

PS. Many might suggest a crawl space but we have already had the slab engineered

If you're dead-set on the venting blowing the heated or cooled air upwards, then you could consider running the duct-work in the foundation itself. This is not uncommon.

Also not uncommon is running the duct-work above the ground floor so that the vents blow downward.

... or am I missing something?