Leaking low pitched roofs are less common than on flat roofed buildings.
Even a 10 degree incline is usually sufficient to ensure a satisfactory dispersal of incidental rainwater.
When leaks do occur, the two most common sources of ingress will be either at the junction of the high point of the roof and any adjoining valley, roof or vertical surface, or close to the bottom edge of the roof – where there may be a subtle flattening of the incline to accommodate a fillet or batoning to which are fixed barge-boards or gutter brackets etc.
Where roofing felt, EPDM, or other sheet materials are in situ, look for splits at those points mentioned above; also look for for lifted edges along upstands and seams.
If tiled or slated – check for units that may have been dislodged from the under-batoning; also look for slates or tiles that may be broken or just cracked on the surface. Even a small crack can be the source of water migrating into the lining or voids in a roof.
A useful tip is to use a piece of timber baton wrapped in a bit of old polypropolene sack or tarpaulin offcut to act as a “dam” to catch any drips; these can then be worked back into the Rubba-Roof Reinforcing Fleece.