Skylight or light shelf? Best daylighting strategy for a passive ADU in zone 6 – GreenBuildingAdvisor

Hi everyone,

I’m designing an ADU in Climate Zone 6 (Portland, ME) and targeting Passive House level performance. I want to bring more daylight into the deeper interior spaces, but I’m concerned about the energy penalty that skylights can introduce in a cold climate.

For a Passive House project in Zone 6, which strategy generally performs better without compromising thermal performance or airtightness?

1. A small, high-performance triple pane skylight

OR

2. A south-facing light shelf with exterior overhang designed to bounce light deeper into the space

I’m trying to avoid both winter heat loss and summer overheating, while still improving interior daylighting.

If anyone has experience comparing skylights vs  light shelves in cold climates or suggestions, I’d appreciate any insight.

Thank you!

@Michellebuenoarch