We are trying to achieve LEED CI v2009 Certification. The project is a 6,237 SF office space tenant in a 336,510 SF building occupying approximately 50% of the 11th floor. We are 3 weeks into construction and have identified a possible issue affecting IAQ:

The existing main HVAC duct is insulated on the outside of the duct and is not currently foil wrapped. Is this exposed insulation in an open return plenum a concern?

The present suite location causes some return air flow from the adjacent spaces to enter the return air ceiling space above the suite, via return air transfer boots. We believe that, for LEED, we can emphasize the LEED project boundaries to prevent a complete mitigation of the main duct insulation on this floor.

Within our space limits, if the existing condition of the bare, unwrapped duct insulation around the main core duct is problematic for USGBC, our mechanical engineer is suggesting that we keep the existing 'bare' insulation and cover it with a FSK (foil-scrim-kraft) paper cover only, instead of replacing the existing with new foil-faced insulation, due to the cost.

Can anyone offer advice in this situation?