The use of these roofing underlays/membranes and requirements for ventilation depend on other factors, often outside the control of the roofer, so these must be considered.
If the roof covering is not sufficiently ‘air open’, then ventilation openings will need to be provided anyway. It might be argued that air permeable membranes are more effective in allowing the dissipation of moisture, but their use needs to be considered in the tile fixing specification as there will be increased wind loading on the tiles.
If there is any doubt about the permeability of the ceiling construction or air openness of the outer roof covering, then ventilation openings should be provided.
