External Wall Insulation is not classed as an extension to the building walls as you are only adding another layer and increasing the depth of the wall by around 2 to 3 inches. However, this often means some degree of alteration to exterior fittings and fixtures and as such a Building Notice is required under L1B of the Building Regs.
In the vast majority of cases you only need to serve the Council’s Building Control with a Building Notice under Building Regs L1B and the Inspector from Building Control will pop along on the first day to meet the installer and again at the end of the job to sign it off and give you an Approval Certificate.
If your house boundary directly abuts a public pavement or pathway then the extra depth to your home can be viewed as an encroachment onto public space and so you will need to apply for Planning Permission.
If your home is listed, is in an Area of Outstanding Beauty or a Conservation Area then again you must apply for Planning Permission before work is started.
We are very experienced in working with the Building Inspectors and can answer their questions on your behalf and we also provide product drawings and specifications for the Planning Department upon request.