9.18.5.1 — Drainage

(1) Unless it can be shown to be unnecessary, drainage shall be provided at the bottom of every foundation wall that contains the building interior. (2) Except as provided in Sentences (4) and (5), where the insulation on a foundation wall extends to more than 900 mm below the adjacent exterior ground level, (a) a drainage layer shall be installed adjacent to the exterior surface of a foundation wall consisting of, (i) not less than 19 mm mineral fibre insulation with a density of not less than 57 kg/m3, or (ii) not less than 100 mm of free draining granular material, or (b) a system shall be installed that can be shown to provide equivalent performance to that provided by the materials described in Clause (a). (3) Where mineral fibre insulation, crushed rock backfill or other drainage layer medium is provided adjacent to the exterior surface of a foundation wall, (a) the insulation, backfill or other drainage layer medium shall extend to the footing level to facilitate drainage of ground water to the foundation drainage system, and (b) any pyritic material in the crushed rock shall be limited to a concentration that will not damage the building to a degree that would adversely affect its stability or the performance of assemblies separating dissimilar environments. (4) Except when the insulation provides the drainage layer required in Clause (2)(a), when exterior insulation is provided, the drainage layer shall be installed on the exterior face of the insulation. (5) The drainage layer required in Sentence (2) is not required, (a) when the foundation wall is not required to be dampproofed, or (b) when the foundation wall is waterproofed. (6) Where drainage is required in Sentence (1), the drainage shall conform to Subsection 9.14.3. or 9.14.4.