Space above ceiling used as non ducted plenum returns

[engprosinc]

I am working on a 1200 sq ft addition to a commercial (bank) building with masonry walls with wooden roof trusses. There is no sprinkler system in the building. Nothing will be stored above the dropped ceiling. The insulation is on the roof, so there will be no insulation in the space above the ceiling. ACT will be installed for the ceiling. All wiring and plumbing above the ceiling will be plenum rated (no PVC, etc.).

Can the space above the ceiling be used as an HVAC plenum return? Sheet metal supply ducts will be installed for all supply diffusers from the RTU. The RTU is 2.5 tons.

 

[steveray]

All new HVAC or just the addition? Codes in effect?

 

[Lucien Benson]

It depends how much space you have. If you are willing to use the space for hvac consult a HVAC service New Jersey technician and seek advice from him. If possible show the area where you are willing to install HVAC.