FAQ
Check the back of the tile as some manufacturers will state the profile, if you are unsure please contact a roofer or send Ubbink UK a picture with dims and we can help identify.
Free Vent Area is the total unobstructed area within a vent opening which air can freely flow. Having a larger free vent area means less vents are needed to meet the local legislation saving cost to your project and install time.
The British Standard BS5250:2021 
A vent will allow natural ventilation into the roof void to meet BS5250 standards maitaing a healthy cold roof void. Terminals and connected to ducting offering supply or extract to an mechancial fan or system. There will be different requirements depending on the size of the roof and the output of the fan being terminated.