I had a new envirotech eva flat roof professionally installed three years. Where it meets with my neighbours on our semi detached houses it has started to leak. On examination the join where it meets has started to detach. The envirotech Eva is overlaid on the felt and it appears the contractor has used some form of adhesive to connect the two materials. Does anyone know if this was the correct method and can anyone advise a solution. The contractor guarantees the installation for 10 years against water ingress.