Framing a ceiling service cavity
Planning stage of a new construction… I’d like some input and suggestions on the best way to frame a service cavity in the ceiling. Here are the pertinent planned details of the house…
Simple rectangle with 51’6″ x 40’6″ rough framing dimensions (exterior).
Trussed gable roof with a single ridge running the length of the 51’6″ dimension. Raised heel trusses for insulation. Truss span will be 40’6″ with no load bearing in between.
Vented unconditioned attic. No ducts or mechanicals in the attic.
2×6 exterior walls with liquid flashed ZIP sheathing for an air barrier.
So my question(s) is this…
Once the trusses are in place, I want to attach ZIP or OSB to the bottom of the bottom truss chords to create the air barrier and then create a lowered ceiling below that. Is this practical? Does it make sense to use drywall here instead of OSB for the price?
What’s the (a)best and (b)most economical way to frame the lowered ceiling in this situation that will support the drywall while ensuring the integrity of the ZIP / OSB air barrier above?
House will likely use ductless mini-splits (possibly ducted if service cavity is used) so the primary purpose of the service cavity would be for ERV ducts. Is there a better method for this?
I suppose a better question might be…is the added cost of building a service cavity worth it if all I need is space for ventilation ducts? Would small soffits only where the ducts are needed make more sense?
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