Insulation Board Application

[i_a_b39]

Hi there. I’m wanting to put insulation board, internally, on my external walls. These are cavity walls. I’m looking for advice on how to apply them. Someone has already suggested I create strapping and put the boards onto that in order to create a gap between the wall to help with possible condensation. However, I’ve read that using an adhesive is the best option. The walls currently are plasterboard with wall paper. Will I need to expose brick work for either method? Thanks