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The granular layer technique is applicable to any type of foundation that includes a sump. Drainage layers may be applied to the outside of the basement wall to direct any infiltrating rainwater that comes into contact with the foundation wall down to the drain pipe or granular layer and away from the wall. Consult the local building department to determine whether drainage layers or membranes are required. Wall drainage layers normally consist of 19 mm (3⁄4 in.) or thicker mineral-fibre insulation with a density of at least 57 kg/m3 (3.6 lb./cu. ft.) or other commercially available wall drainage materials. Alternatively, free-draining granular material may be used as backfill. It is important that the drainage layer direct water to the drain pipe, avoiding any ponding at the base of the
foundation wall. The granular fill surrounding the drain pipe should also cover the drainage layer at the base of the wall. Basement windows that extend below ground level require window wells (Figure 51) to direct water away from them. Corrugated steel frames are commonly used for this purpose. When the backfill is not a granular material, the bottom of the window well should be drained by a pipe or hole 150 mm (6 in) in diameter installed through the backfill material to the drain pipe and filled with crushed stone. Where a bedroom window with sliders, casement or inward-opening awning opens into a window well, it must have a clearance of at least 760 mm (30 in.) in front of the
51 Window well at basement wall provide adequate clearance for escape from egress window building foundation slope directing surface drainage away from building basement window corrugated metal window well anchored to foundation backfill
drainage tile filled with crushed stone leading to weeping tile