One balcony joist bay vent, or two required?

[Yikes]

There was a previous thread where we had discussed continuous balcony vents, and up until now, I assumed that only one continuous vent was required per CBC 2304.12.2.5, which states:
2304.12.2.5 Ventilation Beneath Balcony or Elevated Walking Surfaces

Enclosed framing in exterior balconies and elevated walking surfaces that have weather-exposed surfaces shall be provided with openings that provide a net free cross-ventilation area not less than 1/150 of the area of each separate space.​

The example below from page 90 of the WoodWorks Council seminar on balcony design likewise shows only one long vent.

​

However, on a balcony framed with conventional lumber joists (not open-web trusses), does the phrase "cross-ventilation area" imply at least two rows of continuous vents?

Example: a cantilevered balcony 6' deep, made of 2x12 joists @ 16" o/c. Each joist bay is 14.5" wide x 71.5"long, and has no insulation in it.
A continuous soffit vent like the one shown below runs along the middle of the bay. Because it is going across the entire 14.5" width, is it considered a cross-ventilating soffit?
Or do I need one continuous vent at the back and one at the front in order to get ventilation across the entire 71.5" long direction?



Thanks in advance.

 

[Yankee Chronicler]

How can you have cross ventilation with the vent on only one side?

 

[ICE]

How would convection work if all the vents are at the same elevation? I’ve built miles of balcony soffit that had one or none.

 

[Yikes]

How would convection work if all the vents are at the same elevation? I’ve built miles of balcony soffit that had one or none.

Right. The phrase "cross-ventilation" is not defined in CBC 202.
Maybe the hoped-for air movement in the cavity is achieved not by convection, but just by some hope that turbulent airflow against the balcony on a breezy day will help.

A superintendent on my current multifamily project is asking me the question, because on his last project the inspector made him add a second vent and cited the phrase "cross-ventilation".

 

[Yikes]

How can you have cross ventilation with the vent on only one side?

Good question. It didn't say which way the ventilation has to cross. In post #1 with the Vulcan continuous vent, it cross-vents on the short axis of the joist bay. If the balcony is 6' across, that means that no part of the joist bay is more than 3' away from a vent.
Compare that to CBC 1202.2.1, where the entire top 3' of an attic can be without vents.
So is a continuous vent providing "cross ventilation" if it is continuous across a 14.5" wide joist bay that is less than 6' long?