Insulating a 1930s semi

[wwwebber]

I used 50mm insulated plasterboard dot and dabbed directly onto all external walls in an 1880s house. Not had a single problem, toasty and quiet.

 

[Leofric]

If you look on the websites of insulation companies they have technical data sheets giving information on the recommended details for adding insulation to the inner face of external walls using their products. You should be able to see the U values achieved by different thicknesses of insulation depending on the existing wall construction.