Rule of thumbRecommended
3-way switches at every entrance to every room ≥ 100 sqft AND at top + bottom of every stair
ROT/EXT-THREE-WAY-SWITCH-LOCATIONSDescription
Every room ≥ 100 sqft with two entrances should have 3-way switches at both entries — the user can illuminate the room from wherever they enter. Same for halls + stairs: 3-way switch at top + bottom of every stair, and at both ends of any hall over 10 ft. 4-way switches for halls + rooms with 3+ entries.
Why this exists
Inconvenient lighting is a daily-use frustration. The 3-way switch rule is cheap to design in + costly to retrofit. Architects should explicitly note 3-way pairs on the electrical plan.
Categories
ElectricalCirculation
Source
Professional consensusno manifest entry
IES Residential Lighting Design (—)
Section: Residential design conventions
Published 2024-01-01 · last verified 2026-05-15
Solver enforcement
Browsable only — the solver does not currently enforce this directive (no spec-level data to check against). This entry exists so the architect personas can cite it in conversation and the user can read what the rule says.
Related directives
- Dining room sizing · DINING-ROOM-SIZE
- Mudroom sizing · MUDROOM-SIZE
- Half bath near public zones · HALF-BATH-NEAR-PUBLIC
- Stairs not from bedrooms · STAIRS-NOT-FROM-BEDROOM
- Hallway budget 6-12% of total · HALLWAY-BUDGET
Last reviewed 2026-05-15.