Reduced-rating the conversion of premises to a different residential use: apportionment
The relevant law
Paragraph 1(3) says an apportionment ‘may be made’. A contractor therefore has the option as to whether or not to make an apportionment. If he chooses not to do so, then his supply is wholly standard-rated.
This may occur when works go beyond the immediate site. Where work includes work beyond the property boundaries or away from the curtilage of the building (if the site is large) then the off-site or off-curtilage proportion should be excluded from the reduced rate.