It measures the building, not the household
What it measures
The fabric and the heating system at a standard assumed occupancy. Nothing about how you actually live in it.
What it is useful for
Comparing two buildings, and the recommendations page, which is often the most practical energy advice available for that specific house.
What it is not useful for
Predicting your bills. The assumed occupancy is a family heating to twenty-one degrees for a fixed pattern that suits almost nobody.
