Stop damp and wet ingress by installing approved products when building an extension.
Type E Cavitrays above flat roof intersections and Type X Cavitrays above sloping abutments.
Both have been awarded European Technical Approval and are manufactured by the UK cavity tray specialist.
Now there is an accompanying remedy for overcoming dampness at floor level where the original outside wall is exposed.
Access levels and regulations addressed at the same time, for cavity or solid walls.
Ask for the new Technical Manual.