The following provisions apply to the interpretation of "house", "flat" and "dwelling-house" when used in this Part.
A dwelling-house is a house if, and only if, it (or so much of its as does not consist of land included by virtue of section 184) is a structure reasonably so called; so that—
where a building is divided horizontally, the flats or other units into which it is divided are not houses;
where a building is divided vertically, the units into which it is divided may be houses;
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.
A dwelling-house which is not a house is a flat.