Our customer reported a bad leak into the plaster board ceiling of their home office which had been converted from a garage. This happened after their neighbour had work carried out on the adjoining flat roof.
It seems that the garage originally had an internal drain pipe carrying water from the flat roof through the garage to the drain but this pipe had been removed many years ago. When the builders did the garage conversion they didn't spot the hole where the drain pipe had been removed and plasterboarded the inside of the garage ceiling.
When the neighbour had work done, their contractor failed to seal the gap between our clients roof and theirs resulting in water leaking under the felt on the garage conversion. Eventually it found its way down the hole, through the insulation, and into the plasterboard.
We removed the entire roof and found the beams to be OK. We replaced the boards, fitted new ones, and installed a new Firestone rubber roof before ensuring the joins to the property and next door were all correctly sealed. The client now has a roof that will last for many years and can now get the office ceiling repaired knowing that there will be no more water entering the property.
There a couple of useful things to note: