Architecture
Window-to-Wall Ratio (WWR)
IECC caps prescriptive WWR at 30-40%. Above that you need performance compliance. Plug in window areas + wall area by elevation, get the WWR and compliance check.
FAQ
What counts as fenestration? +
All glazed openings in exterior walls: windows, glass doors, curtain wall vision glass, skylights (technically separate cap). Spandrels are NOT fenestration.
What if I exceed 30%? +
Switch from prescriptive to performance compliance. You'll need an energy model (eQuest, IES, EnergyPlus) showing total building energy use is no worse than the prescriptive baseline.
What about ASHRAE 90.1? +
Same general approach: 40% prescriptive cap for commercial. Performance path lets you go higher with offsetting envelope improvements.