As per title, need to construct a stud wall with an opening for a 610x1981 FireDoor (which I'll probably get someone to fit and sign off). Will buy a suitable FD30 lining at the same time, (30mm thick), but I need to know how big to make the opening in the stud wall to accomodate this. The chap on the end of the phone is telling me I need an opening of width 610+30+30 but I don't have faith in that - surely I need a slightly bigger one?