outbuilding got flat roof roughly 5 pitch angle. it got double layer osb3 which it got double 18mm (total 36mm thick) with roof felt with roof adhesive sealing also it already got roof underlay which it under the osb . it well prefect. and also it got fascia round the building. but there water ingress there. what it cause problem?? please help?
it could be condensation, giving the illusion of water ingress, try leaving a window slightly open to see if it disappears, or water penetration through the walls, blocked gutter? its a process of elimination, try hosing the roof in area where you think in may be problematic, it could be a tear in the felt