Planning permission is not normally required for fitting insulation.
External wall insulation
External wall insulation does not require planning permission providing it does not project from the wall of the house by more than 16cm.
However, if the building is listed or is in a conservation area you should consult your local planning authority.
Disclaimer - Wales
This is an introductory guide and is not a definitive source of legal information. This guidance relates to the planning regime for Wales. Policy in England may differ. If in doubt contact your Local Planning Authority.