(1)The following provisions apply to the interpretation of "house", "flat", "dwelling-house" and "relevant time" when used in this Chapter.
(2)A dwelling-house is a house if, and only if, it (or so much of it as does not consist of land included by virtue of section 50(2) of this Act) is a structure reasonably so called; so that—
(a)where a building is divided horizontally, the flats or other units into which it is divided are not houses; and
(b)where a building is divided vertically, the units into which it is divided may be houses; and
(c)where a building is not structurally detached it is not a house if a material part of it lies above or below the remainder of the structure.
(3)Any dwelling-house which is not a house is a flat.
(4)There shall be treated as included in the dwelling-house any land used for the purposes of the dwelling-house which the landlord and the tenant agree to include.
(5)The relevant time is the date on which the tenant's notice claiming to exercise the right to buy is served; except that, if that notice is served within six months of the commencement of this Chapter, the relevant time is the date on which this Act is passed.