"I am hearing R8 is optimum" quite the contrary, R8 is often the minimum. "When located within the building envelope assembly, at least R-8 shall be applied between the duct and that portion of the assembly farthest from the conditioned space."..... at least j

I'm confused - does that specify a minimum building assembly R value of 8 if any ductwork exists in the space?

If they want R8 around ducts in conditioned space, what do they want for ducts outside of conditioned space 12? 16? 20?

What I heard was r4 was code for unconditioned spaces and they then upped it to r8. I could see where on long runs, you would want to insulate but I don't know of any codes. Not that codes are any more than minimums. Anyone got sources?

Codes vary by state and local jurisdiction - you'll need guidance specific to your area

Aren't all the states now doing National code?

Sources?
I quoted the MRC (Michigan amended IRC or international residential code). Most of it is the same as the
IRC, but I wouldn't know which parts were exclusive to MI.
Here is the duct insulation info.
1601.3.4 ".....following requirements...."
1) "vapor retarder.....on exterior of insulation on cooling supply ducts that pass through nonconditioned spaces conducive to condensation."
2) "Exterior duct systems shall be protected against the elements."
3) "....coverings shall not penetrate a fireblocked wall or floor."
4) "All....shall be insulated...to R5 when system components are located within the building but outside conditioned space and R-8 when located outside the building. When within a building.....at least R8....between the duct and...(surface) farthest from the conditioned space."
Exception: Exhaust...ducts...

There is some ambiguity, you can check IRC yourself or whatever local enforcing agency follows.
It has caused some problems in MI where exterior wall ducts require R8 so you might be trying to get a 3" duct and 2" of insulation in a 3.5" wall cavity....not a good fit.

The exhaust duct exception is unfortunate in my mind as well as condensation issues can arise both in and out of the pipe.

Many portions of codes are ambiguous or even conflicting.

IMO the thrust of this section is 90% condensation and 10% conservation. There is certainly nothing to prevent a home owner from throwing an extra blanket over attic ducts, but where insulation is concerned, I would not expect more than code minimum from your contractor. Diminishing returns apply as well, extra money spent on insulating window blinds, may save more than moving from R8 to R19 on your ducts.
j

I will be insulating my ducts. a chance to save labor costs and I will be fussy enough to spend time doing it completely. My thought is to get a kit and go crazy doing the closed cell around the duct and down to the ceiling under the duct. leave the original fiberglass in place as a release from the sheetrock. Was planning flex from trunk to register but may just do in metal and insulate. foam and maybe throw the old batts on top instead of tossing. I will be making a foam hatch for the fold up attic stairs too.