The energy assessment is based on building regulations.
These standards have changed dramatically over the last 100 years.
When an EPC states that the walls are insulated (assumed), this means that the energy assessor has stated that the property is a certain age, that the minimum building regulations at that time would have required the walls to be insulated and that they meet a particular u-value
(thermal value).
There would be no other signs of extra insulation so the assessor has ticked ‘as built’.
