protected enclosure

For a protected corridor, do you need to put 2 layers of fireline plasterboard on both side of the timber wall? Or can you just put 2 layer of fireline plasterboard on the protected corridor side and one layer of normal plasterboard on the other side ?

hi, I am renovating an old house which has a mixture of brick and timber stud walls with Lathe and plaster. Some day, I might like to do a loft conversion. To do this I'm pretty sure I'll need the stairwell to be a 'protected enclosure' will all walls having at least 30min fire resistance. In...