We have a flat roof garage. It is single brick with cement coating on the inside. With all the rain we have been having we noticed a large patch of damp cement on the inside of the garage starting about 1 metre down from the roof. On the outside of the roof we have the metal ridged sheets, then felt and then wooden boards. From the inside the roof is dry and the top of the wall. When we went up on the roof everything looks fine can't see any problems. But my neighbour thought that between my garage and next door's there is a 5inch gap so rain does go down there. When the garage was built about 17 years ago on the outside of the wall large blobs of cement were left on the bricks so my neighbour thinks that because we have had the 4 wettest months that when is rains the blobs of cement are getting wet and the water is soaking through into the inside. Due to lack of dry weather these blobs of cement are not drying out just constantly staying wet. We have not had any previous problems. Could this be the answer or is it more likely to be the roof? Due to there being a 5inch gap between the garages only able to look down form the roof. Would putting guttering on the side of the garage help the problem.
Any advice would be greatly appreciated