Roof underlay sagging into gutters and undersized battens
What it looks like
Water tracking behind the fascia, staining at the eaves, or tile courses that lift and rattle in wind.
Why it happens
Underlay not supported at the eaves, no eaves carrier tray, battens below the required section or nailed with the wrong fixings, and tile fixing specification not followed for the exposure zone.
What it costs if it is missed
Water entry at eaves, premature timber decay and, in exposed locations, wind uplift of tiles.
How to inspect for it
Check before tiling: eaves carrier fitted, underlay drape correct, batten size and grade marked, fixing centres and clip specification matching the wind uplift calculation for the site.
How to prevent it
Obtain the fixing specification for the actual site exposure before the roof starts, and inspect the first slope as a benchmark for the plots that follow.
Basis in regulation
Last updated 23 August 2026. This is our editorial summary of publicly available regulation and site practice, not building control approval or a warranty determination.