The terms renovation, refurbishment and retrofit are often taken to mean the same thing, or used as if they are interchangeable. However, they have different specific meanings:
Retrofitting means “providing something with a component or feature not fitted during manufacture or adding something that it did not have when first constructed” (Ref Retrofit 2050: Critical challenges for urban transitions). It is often used in relation to the installation of new building systems, such as heating systems, but it might also refer to the fabric of a building, for example, retrofitting insulation or double glazing.
Refurbishment on the other hand implies a process of improvement by cleaning, decorating, and re-equipping. It may include elements of retrofitting.