Advice on attic options (Climate Zone 2) – GreenBuildingAdvisor

Long-time reader, first-time poster. Thanks to everyone active in these forums; I’ve learned a lot from the discussions here!

I have secured land to build a small (1,200 sq. ft.) high-performance home in Lafayette, Louisiana. I am weighing three options for the attic assembly and would love some advice:

1. Conditioned Attic: Mineral wool batts against the roof deck with a vapor diffusion port at the ridge & supply air to the attic. Main downside: high cost of mineral wool insulation.

2. Sealed, Unconditioned Attic: Insulation at the ceiling plane with buried ductwork and a vapor diffusion port. This is the cheapest option, but I worry about long-term condensation risk if ducts ever start to leak.

3. Vented Attic with Plenum Trusses: Bring ductwork into the conditioned space and achieve air sealing using the detail from this FHB article. I have two concerns with this approach:

* Requires a structural engineer to design a truss-to-wall connection that meets Louisiana’s wind uplift requirements which adds to cost.

* Scheduling: Complicates the workflow, requiring framers and drywallers to make multiple trips to finish the plenum and interior ceiling.

I believe options 1 & 3 are similar in cost, and I like that option 1 gives me easier access to the attic for maintenance and ability to place mechanical equipment in the attic. My Manual J analysis shows similar cooling loads across all three approaches.

Any thoughts on which approach balances risk and buildability best for this climate?