I found a TOH article describing how to install beadboard on a porch ceiling, but one thing they don't talk about is ventilation.

On our porch, the space above the ceiling is not part of an attic attached to the house, it is just exterior empty space. Currently, the aluminum ceiling has a large vent section running the length of the house. If we replace the aluminum with beadboard, how do we continue to provide good ventilation? Our roof is new, and uses soffit vents. We would like to run the beadboard perpendicular to the house rather than parallel like it is currently.

Any help would be appreciated! Thanks!