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Ian McChesneyHi Sarah
Attached is an article from Build magazine from a few years ago about roof underlay. BRANZ has further information that might be helpful as well.
As the article suggests, underlay has multiple purposes – providing a second line of defence against any water leak from the roof and a collector/channel for condensation, reducing draftiness, and reducing ingress of dust/debris.
Houses vary in being prone to roofing condensation, draftiness etc. So ripped underlay may not present any immediate issues in some houses. In others it might result in any leakage or condensation being channelled into the ceiling space rather than out to the guttering, and increase ceiling cavity draftiness, debris etc.
regards
Ian
