A drainage inspection assesses how effectively a property manages water from rainfall, groundwater, and plumbing discharge. Proper drainage directs water away from the building's foundation and prevents accumulation in areas where it can cause structural damage, erosion, damp conditions, or pest problems. Poor drainage is one of the most common contributors to building defects and is a frequent finding in building inspections.
What the Inspection Covers
A drainage inspection examines surface grading and fall direction around the building, gutters and downpipes, stormwater drainage pits and pipes, subsoil drainage (agricultural drains), retaining wall drainage, and the overall site's ability to shed water away from structures. The inspector looks for signs of inadequate drainage including ponding water, erosion channels, damp at the base of walls, water staining, and vegetation patterns that indicate persistent moisture.
Surface Drainage
The ground surrounding a building should slope away from the foundation to prevent water from pooling against walls and footings. Minimum fall recommendations vary by jurisdiction but typically call for at least a 1-2% gradient away from the building for the first few metres. Paved areas, garden beds, and landscaping features that direct water toward the building are common issues identified during inspection.
Subsurface Drainage
Subsurface or agricultural drainage systems are installed below ground to manage the water table and prevent rising damp and hydrostatic pressure against foundations. These systems use perforated pipes set in gravel beds to collect and redirect groundwater. Over time, subsurface drains can become blocked by roots, silt, or crushed pipes, leading to drainage failure that may not be immediately visible at the surface.
Drainage and Pest Risk
Inadequate drainage creates moisture conditions that are highly conducive to mold growth and termite activity. Standing water attracts mosquitoes, and consistently damp soil against a building increases the risk of subterranean termite entry. Addressing drainage deficiencies is often a key recommendation in pest management plans.