Vent placement: high, low, and ridge options
Why a single vent never works, what to use for low inlets and high outlets, and where ridge vents earn their cost.
Ventilation in a coop is a two-port system. Air enters one place, leaves another. A coop with vents on only one wall has air sitting still, regardless of total square inches.
Low inlets sit near the floor, ideally on the windward wall so prevailing wind helps. Pull cool fresh air in below roost height. Louvered vents handle this well because they shed rain. Hardware cloth over a framed opening also works for keepers who prefer maximum airflow over weatherproofing.
High outlets sit at or near the ridge. Warm air rises, picks up moisture, and leaves through these openings. The outlet area should match the inlet area, roughly half the total vent area each. Gable vents, soffit vents, and ridge vents all qualify.
Ridge vents earn their cost in two situations: tall coops where the ridge is hard to reach for seasonal adjustment, and humid climates where keepers want the maximum continuous outlet. They are more expensive than two gable vents but they remove the ladder.
The 50/50 inlet/outlet split is a starting point, not a law. In hot humid climates, lean a little heavier on outlet area. In cold dry climates, lean a little heavier on inlet area. The calculator handles the basic split, you tune from there.