The ventilation of mono-pitched roofs at ceiling level only may allow air to stagnate at the apex of the roof. To prevent this, high level or ridge ventilation, equivalent in total area to that given in the table, should be provided in addition to the ventilation at ceiling level.
Similarly, air stagnation may occur in duo-pitched roofs of more than 20 degree pitch, or 10.00m span and consideration should be given to the provision of additional high level or ridge ventilation, equivalent to a continuous gap 5mm wide.
When insulation material is close to the roof covering, as at the eaves, or where it is placed at rafter level to form a warm roof space, (as in attic and
raised tie construction),