Insulating and Warming up An Extension

[Skavenger]

I have a great 1925 brick built end terrace house with cavity walls. In the 1970s an extension was added to the back of the house to add a kitchen and above it a bathroom with a flat “cold” roof.
Both the kitchen and especially the bathroom suffer with really bad condensation and cold, particularly on the gable end wall which faces west.

I really need to make the bathroom comfortable as in the winter showering or bathing is not a pleasant experience.

To insulate the bathroom I was considering having the exterior clad with either Fortex or Hardie Cement Board and wondered whether I can insulated behind this cladding or not. Doing so would surley make the internal walls warmer and cut down the condensation would it not?

The house has central heating and double glazing but there are no radiators in the bathroom or kitchen.

There are extractors in the kitchen but none in the bathroom. When we redo the bathroom I intend to fit an extractor.

The facia boards on the bathroom exterior need renewing especially on the weather west side so when the roof gets redone it needs to be changed to warm roof. If this increases the roof height will it need planning permission

 

[foxhole]

Insulated plasterboard to interior would be easier and the bathroom needs a radiator. Both need good extraction to avoid condensation and mold problems .