A building or structure is in “qualifying use” for the purposes of this Part if it is in non-residential use for the purposes of a qualifying activity carried out by the person who has the relevant interest in the building or structure.

But a building or structure is not treated for the purposes of subsection (1) as being in use for the purposes of a particular activity if the extent to which it is in use for those purposes is insignificant.

The extent to which a building or structure is in use for the purposes of a particular activity is to be determined on a just and reasonable basis.

Section 270EB makes provision for the calculation of the allowance in the case of a building or structure that is put to multiple uses.