Energy-code path: prescriptive vs. performance

What governs

Oregon adopts the Oregon Residential Specialty Code (ORSC) with the Oregon Energy Efficiency Specialty Code (OEESC) as its energy chapter. The 2023 cycle is in effect and meaningfully stricter than 2017 — it pushes hard toward heat pumps and tighter envelopes.

You comply one of two ways:

1. Prescriptive. Follow a checklist of minimum R-values, U-factors, and equipment efficiencies. Easiest for small DADUs. Submitted as a REScheck or equivalent worksheet.
2. Performance. Hire an energy modeler to show the design beats the prescriptive baseline by some margin. Adds $1,500-$3,000 in modeling fees, but gives you flexibility (bigger windows in exchange for better insulation elsewhere, for example).

What it drives

• Wall assembly: typical 2x6 with R-21 cavity + R-5 continuous exterior insulation
• Windows: U-0.27 max, with SHGC limits depending on orientation
• Air sealing: blower-door test ≤3.0 ACH50 commonly required
• Mechanical: heat pump strongly preferred (essentially required to pass the prescriptive path on small units)

How to pick

• Standard rectangular DADU, conventional windows, all-electric? Prescriptive — you'll sail through.
• Larger windows on a south-facing view, vaulted ceiling, or an unusual envelope? Performance, so you can trade off.