As far as I know PU injection means injecting some substance through some areas perimeter of the walls or ceiling through some holes
And these substance will fill up crack or holes
Anyone can correct me if I wrong
Better ask where the root cause
If rooftop tiles break then need to replace rooftop tiles
If concrete slab then maybe PU injection is not a bad idea
My kitchen extension side walls is leaking badly during heavy thunderstorm. Above is concrete slab.
Suspect is the joint between slab floor with wall side but I dunno
So now I paint waterproofing and it stop the leak