Definitions: Thermal element

"Thermal element" means a wall, floor or roof (but does not include windows, doors, roof windows or rooflights) which separates a thermally conditioned space from— (a) the external environment including the ground; or (b) in the case of floors and walls, another part of the building which is— (i) thermally unconditioned; (ii) an extension falling within Class 8 of Schedule 2; or (iii) in the case of a building other than a dwelling, conditioned to a different temperature, and includes all parts of the element between the surface bounding the conditioned space and the external environment or other part of the building as the case may be;