Source of seepage
AC drain lines
Condensate water from split AC indoor units
How water travels
From the source to your wall.
A split AC's indoor unit collects condensate in a tray and drains it through a pipe, usually run outside through the wall or concealed in the wall to a drain point. If the pipe is blocked, kinked, not sloped, disconnected inside the wall, or simply left to drip onto a ledge or the wall face outside, water soaks into the wall below the unit or into the external wall. Upstairs units dripping onto a lower ledge can wet another flat's wall.
When it shows: Summer and the humid months when ACs run most.
The pattern it leaves
- Damp patch directly below an indoor AC unit
- Damp running down along the line of a concealed drain pipe
- Damp on the outside wall below the pipe outlet, sometimes showing inside
- Worse in the months the AC is used heavily, not tied to rain
- Stains on the ceiling below an upstairs flat's AC position
How it's confirmed
Meter, thermal, eyes.
- Meter readings below and around the indoor unit and along the likely pipe route, against the dry reference
- Thermal scan of the wall, ideally with the AC running, though cold air from the unit can cool the wall around it without any leak, so every cool area is confirmed with the meter
- Visual check of the drain pipe outlet, its slope and whether it drips onto the wall
- Checking the tray and pipe connection where visible without opening the unit
Who is usually responsible
It depends on where the water starts.
- Owner
- Usually responsible for the AC and its drain line, including drips onto the wall of a neighbour's flat.
- Neighbour above
- Usually responsible if their AC drain wets your wall or ledge, depending on the society's bye-laws, which vary.
- Tenant
- In a rented flat, routine upkeep of an AC the tenant uses may fall to the tenant, depending on the rent agreement and your state's tenancy law.
Typical repair approach
What a fix usually involves.
Described for understanding, not as a recommendation. Megahedge does not do repairs or recommend contractors.
- 01Clearing the drain pipe and tray
- 02Re-routing the pipe with a steady fall to a proper drain point instead of letting it drip on the wall
- 03Replacing a disconnected or cracked concealed section
- 04Drying and repairing the affected plaster
Questions buyers ask
Can an AC really cause wall damp?
Yes. A split AC produces a steady stream of condensate in humid weather, and if it does not drain properly it soaks into the wall.
Do you open the AC unit?
No. The inspector checks the wall, the visible pipe and its outlet. Servicing the unit is for an AC technician.
The damp is near the AC but it is not running in winter. Can you still tell?
Old damp may still read, and salts and staining help. If it is unclear, the report notes it and a re-scan in the AC season can confirm it.
Find the damp before you pay for it.
Book a moisture and thermal inspection. Report on WhatsApp within 24 hours.