Undrained Air Conditioner Overflow
Split-system and ducted air conditioners produce condensate that must be piped away from the building. Where the overflow line terminates against the wall or discharges onto soil at the perimeter, repeated wetting creates conducive conditions for subfloor moisture, termite activity, and rising damp in adjacent masonry or framing.
Severity rationale
Across 2,254 observations the modal score is 3, recorded in 1,448 cases (64%). Severity 2 accounts for 35%, and severity 4 for only 7 observations (0.3%). Severity 5 is not recorded and the ceiling is 4. The average of 2.65 places this in the moderate band. Most findings are a straightforward pipe extension job; what drives a score toward 4 is evidence of consequential damage - moisture penetration into the wall cavity, staining on internal linings, or termite conducive conditions created at the wet perimeter.
Causes
- Overflow line terminated short - discharging against the wall cladding rather than into a drain
- No overflow piping installed at all, condensate dripping from the unit base onto the perimeter slab or soil
- Original drain connection disconnected during renovation or re-roofing work
- Overflow piped to a location that has since been blocked or raised by landscaping
- Multiple units sharing a single overflow that is undersized or incorrectly fall-graded
Symptoms to look for
- Visible water staining or wet patch on wall cladding or slab below the AC unit
- Overflow pipe terminating against the wall or discharging onto soil within 500 mm of the building
- Efflorescence or rising damp in masonry adjacent to a unit installed on an external wall
- Persistent wet soil at the building perimeter beneath or near the AC installation point
- No visible drain connection or directed outlet for the overflow line
Remedies
- Extend the overflow line to discharge clear of the building perimeter, ideally into a stormwater drain or ag-drain
- Where a drain connection is not feasible, terminate at minimum 1 m from the wall and grade the soil away
- Engage a licensed plumber or air conditioning technician to re-pipe the overflow correctly
- Inspect the wall cavity and subfloor for moisture damage at the affected location
Where we see this most
These suburbs show the highest concentration of undrained air conditioner overflow in our inspection data (minimum five observations). Click a suburb to see its full defect profile.
Worth asking our inspector about this specifically.
This is a plumbing correction rather than a structural repair and is typically low cost. Our inspectors recommend rectification before the first summer cooling season to prevent cumulative perimeter wetting.