“back filling” means the material with which a trench or excavation is refilled;

“butt exposure” means the length of a slate, shingle or tile which is exposed below the edge of the next row of units above when laid on the roof;

“corrosion-resistant” means having the ability to resist gradual chemical or electro-chemical change caused by atmosphere, moisture or other agents;

“damp-roof” means having the ability to prevent passage of moisture in the absence of hydrostatic pressure;

“finished ground-level” means the permanent surface of the ground adjoining the building as distict from the ground-level before commencement of building-operations;

“glazing -bars” means bars made with rebates or of special shapes to support panes of glass in position, and to which the panes may be secured;

“habitable room” means any room designed for human occupation, but excluding bath-rooms, water-closets, stairways, passageways, lift-cars, photographic dark rooms, sculleries, domestic laundries, cold rooms or garages used for parking only;

“roof-pitch” or “roof-slope” means the inclination of a rather or roof to the horizontal measured in degrees of arc;

“safety-glass” means laminated safety-glass, solid heat-treated safety-glass (toughened glass), wired glass or polished wired glass;

“side-lap” or “end-lap” means the distance by which one roofing-unit overlaps the next at its side or end;

“waterproof” means having the ability to prevent the passage of water under hydrostatic head;

“water-table” means the level of the free surface of undisturbed water which will stand in any excavation on the upper limit of the zone of saturation by water in the ground;

“weatherproof” means having the ability to prevent the entry of water into a building under unobstructed conditions of run off.