In summary, the first empty home condition is that the property has been unoccupied for more than two years before works commences.
Provided this condition is met all of the work is reduced-rated. This applies even if the premises start to be lived in while the work is being done. The occupier must, however, move in on a day after the work started, not before (Notice 708, para. 8.3.4 (2014 edn)). If the occupier moves in before work starts reduced rating may be available under the second empty home condition (¶33-780).
The period of non-occupation has been two years since 1 January 2008, before this date it was three years.