Three Alternative Solutions dependant on roof span
Cold roofs with vapour permeable underlays and well-sealed ceilings
The ventilation requirements for cold roofs with vapour permeable underlays (low resistance) and 'normal' ceilings can be met by either a ridge ventilation solution or an eave-to-eave solution for all roof pitches for buildings up to a span of 10 metres. Large buildings with spans greater than 10 metres require eave and ridge ventilation. Providing a well-sealed ceiling reduces the amount of ventilation required.
The ridge ventilation specified in this detail can be used on all roof pitches up to and including building of 10 metres span.
Where the span of the roof is greater than 10 metres eaves ventilation must be added at 5,000 mm2 / m.
Alternatively, eave to eave ventilation of 3,000 mm2 / m. can be provided on roofs of any pitch and up to 10 metres. This is an alternative to the ridge specification given in the first detail above.
