What is the widest house on which a ridge vent will be effective?

Here is some information about width guidelines when using a ridge vent.

The widest house/building the ridge vent can be put on is 75 ft. This assumes the house/building has two gable ends, the ridge vent provides 18 square inches of Net Free Area per linear foot, and the attic ventilation requirement is the 1/300 ratio. The length of the house/building has no limitation, but the maximum width (defined here as eave to ridge to eave horizontally measured footprint of the house regardless of roof pitch) -- s 75 ft. That's the way the numbers work out using building code requirements and the available NFA of the ridge vent. The only way to go wider than 75 feet is to source a commercial style ridge vent that provides more than 18 square inches of NFA per linear foot.