If I have eaves ventilation, do I need ridge ventilation?

When the roof pitch is 35 degrees and above, or when the building is 10 metres wide or more, then the British Standard BS 5250 recommends the use of ridge ventilation combined with eaves ventilation. This actually provides a much more efficient system because air passing over the ridge will draw fresh air into the eaves. When there is only eaves ventilation there needs to be enough wind to force air in through one side of the building and out through the other.