I have 2 sheds in our garden; one is for garden tool storage the other I have made into an office housing my computer and Hi-Fi. Both roofs are covered in felt applied in strips off a roll starting at the bottom edge so the higher ones overlap the lowers. Externally both appear to be intact but both leak in heavy rain. I've tried pinpointing the locations of the leaks from inside the sheds but despite applying sealer externally the leaks occur most times it rains. I appreciate that I will have to apply new covers but would appreciate guidance as to which are the best and longest lasting materials to use. I'm a pensioner so I'd like to keep costs down but reliable leak prevention is more important than cutting cost to the bone. Incidentally both roofs are flat but fall about about 30 cms from back to front. What knowledge I have is about cars, motorcycles and planes; my knowledge of building maintenance is minimal. Any recommendations please??
Robert B

Seal the joints with bitchimun