When using a breathable underlay do you need any other roof ventilation?

It is best practice to ventilate roofs in all situations and our recommendations are in accordance with BS 5250: 'Control of Condensation in Buildings'. Particular consideration should be given to the use of Shingles and Shakes which are a tight fitting roof covering and unlike other roofing products, such as interlocking tiles and double lap plain tiles, do not allow fortuitous air movement through the laps and joins. It is therefore necessary to provide a 50mm ventilated batten cavity above the underlay and below the covering.