Inadequate Surface Water Drainage
Where surface water cannot drain freely away from the building perimeter, it accumulates against footings and walls, creating persistent soil moisture that is a primary conducive condition for termite activity and footing movement. The BCA requires finished ground levels to fall away from the building at a minimum 1:100 grade for at least 1 metre at every external wall.
Severity rationale
The modal score across 902 observations is 3, with 755 findings (84%) sitting at score 3. Score 2 accounts for 115 findings (13%) and typically reflects minor grading issues or cases assessed in dry conditions. Score 4 is present in 31 observations (3%) where active ponding against footings or confirmed sub-floor entry was observed. No score 5 findings exist in the dataset, consistent with this being a conducive condition rather than active structural failure. The score is pushed higher when poor drainage is combined with high termite risk or visible footing distress.
Causes
- Ground levels not graded to fall away from external walls - flat or reverse-fall sites
- Insufficient site grading during original construction or landscaping modification
- Downpipes discharging to surface rather than connecting to a stormwater system
- Poor site drainage or clogged subsurface drains allowing water to pond near footings
- Dry conditions at inspection time preventing full assessment of drainage behaviour
Symptoms to look for
- Ground levels at or above the wall base, with no visible fall away from the structure
- Soil or garden beds sitting against external walls rather than stepping down from them
- Evidence of past ponding - staining, erosion channels, or dead grass along wall lines
- Water appearing to track toward footings during or after rainfall
- Potential for surface water entering sub-floor or rising against perimeter walls
Remedies
- Re-grade garden beds and lawn areas to achieve a minimum 1:100 fall for 1 metre from all external walls
- Assess drainage performance during a rainfall event - deficiency may not be visible in dry conditions
- Engage a plumber or landscaper to assess and rectify where surface water appears to reach sub-floor or pond against walls
- Connect downpipes to the stormwater system if they currently discharge to surface near the building perimeter
- Engage a qualified landscaper for drainage solutions including agricultural drains or detention basins on flat sites
Where we see this most
These suburbs show the highest concentration of inadequate surface water drainage in our inspection data (minimum five observations). Click a suburb to see its full defect profile.
Worth asking our inspector about this specifically.
Poor surface drainage is a low-cost fix that significantly reduces termite conducive conditions. Assess during a rain event if possible, then engage a landscaper or plumber to regrade and connect downpipes before the next wet season.