Few things generate as much friction in a multi-unit building as a leak nobody can source. A stain appears on one owner's ceiling, the unit above says their plumbing is fine, the roof was checked last year, and the committee is left with a growing repair question and no evidence to base a decision on. Shared walls, roofs, balconies and common services mean that water can travel a long way from where it enters to where it shows.
Non-invasive thermal and moisture scanning gives committees and body corporate managers a way to work through that problem methodically. This post covers how moisture and leak detection is used to locate the source of shared-wall, roof, balcony and other general leaks from unknown sources, and why a scheduled annual exterior check helps committees find problems before owners report them.
Why leaks in multi-unit buildings are hard to pin down
In a standalone house, a leak usually has one owner and one building envelope. In an apartment block or townhouse complex, water can enter through the roof, a balcony, a window head or a cladding junction and track along framing, through floor and wall cavities, and across unit boundaries before it becomes visible. The place where a stain shows is often not the place where the water gets in.
That is where disputes start. Unit owners want the problem fixed, the committee needs to know whether it is common property or an individual unit, and anyone commissioning repairs wants to be confident the work is aimed at the right location. Guesswork is expensive, and opening up linings without a clear target can disturb several units for little result.
How non-invasive scanning locates the source
Our moisture and leak detection service combines two methods. A thermal imaging survey scans walls, ceilings, floors and exterior surfaces for temperature patterns that indicate moisture, because wet building materials behave differently from dry ones. Calibrated moisture meters then confirm and measure moisture at the locations the scan identifies, without drilling or cutting into linings.
For a multi-unit building, the value is in how the findings are used. Readings are mapped to specific locations, so the committee can see where moisture is present, how far it extends and which parts of the building it relates to. We explained the same approach for individual homes in our post on how track and trace leak detection finds hidden leaks.
Common leak sources in shared buildings
Shared walls and cladding
Moisture in a party wall or exterior wall can come from failed sealants, flashing details, cladding joints, or services running within the wall. A scan can show whether the moisture pattern follows the exterior envelope, a plumbing run or something else, which helps narrow the investigation before any linings are opened.
Roofs and rooftop penetrations
Roof leaks often show up some distance from the roof defect. Thermal and moisture scanning of ceilings and upper-level walls helps trace the path of the water back toward a likely entry point, such as a flashing, junction or penetration.
Balconies and decks
Enclosed balconies and decks are a recognised area of risk. MBIE's guidance on maintenance notes that balconies enclosed with solid walls often suffer weathertightness problems and need frequent checks for signs of swelling, cracking and corrosion around bolts and flashings, and that drainage outlets should be kept clear. Scanning the adjoining ceilings, walls and floors helps identify whether water is getting in around the balcony.
General leaks from unknown sources
Sometimes the first report is simply damp or staining with no obvious cause. Scanning the affected unit and the surrounding areas helps establish whether the moisture is isolated, tracking from elsewhere, or part of a wider pattern across the building.
Documented evidence for the committee
A committee making decisions on behalf of all owners needs more than an opinion. The written report from a moisture and leak detection inspection includes annotated thermal images, moisture meter readings with locations, plain-language explanations of what each finding means, and recommended next steps.
That record helps committees decide where to focus repair investigation, supports conversations with contractors and insurers, and gives owners visibility of the evidence behind decisions. It may also give the committee a record of how a reported problem was investigated.
Where annual exterior maintenance checks fit
Under the Unit Titles Act 2010, the body corporate is responsible for maintaining common property, and government guidance on unit title maintenance emphasises planning ahead for that work. In practice, that means finding out the condition of the building before problems force the issue.
MBIE's guidance on protecting your investment recommends checking roof cladding, chimneys and flashings once a year, checking cladding regularly for signs of water getting in, keeping balcony and deck drainage clear, and getting involved in body corporate maintenance planning. For homes built since the early 1990s that carry any risk of being leaky, it recommends a careful cladding inspection at least once a year. The guidance is written mainly for homeowners but covers apartments, balconies and body corporates. It is guidance on good practice rather than a requirement that every building be inspected annually, and each body corporate should confirm its own obligations with its manager and lawyer.
An annual exterior check puts that guidance into practice. A scheduled thermal and moisture scan of the building, focused on roofs, balconies, cladding junctions and shared walls, can identify areas of developing moisture before there are stains, complaints or damage to linings. Findings can be fed into the long-term maintenance plan and budget, so repair work is planned and funded rather than reactive. The report also builds a year-by-year record of the building's condition.
Where the question is the overall weathertightness risk of the building envelope, a weathertightness report is the appropriate service, and it can sit alongside annual scanning.
What scanning does and does not do
Scanning locates moisture and helps trace likely sources. It is an assessment, and it does not repair anything. HS Building Inspections does not carry out remedial work, which keeps the findings independent of any repair scope that follows. Where a finding needs further investigation, such as invasive testing or specialist input, the report will say so. Committees should take advice from their body corporate manager and lawyer on how findings affect common property responsibilities and any insurance or legal process.
Planning an inspection in an occupied building
Multi-unit inspections involve access to individual units as well as common areas, so planning ahead helps. Committees or managers can notify owners and tenants of the inspection window, identify the units or areas of concern, and arrange access to roof spaces, balconies and plant areas. Because the method is non-invasive, it does not require linings to be opened.
Frequently asked questions
Does a leak detection scan damage walls or finishes?
No. Thermal imaging and moisture meter readings are taken through existing surfaces without drilling or cutting.
Who is responsible for a leak in a unit title building?
That depends on where the water is entering and what is affected, since common property and individual units are treated differently under the Unit Titles Act and the body corporate rules. A detection report helps establish the location and extent of the moisture, but your body corporate manager or lawyer should advise on responsibility.
How often should a multi-unit building have an exterior check?
MBIE guidance recommends annual checks of roofs and regular checks of cladding, with an annual cladding inspection for buildings built since the early 1990s that carry any risk of being leaky. Many committees adopt an annual scan as a practical way to meet that guidance. It is good practice rather than a general legal requirement.
Can scanning find the exact source of every leak?
Not always. Scanning narrows down the likely source and maps where moisture is present. In some cases further investigation is needed to confirm the entry point, and the report will recommend appropriate next steps.
Can the report be shared with contractors and insurers?
Yes. The report is a written record that the committee can share with its manager, contractors and insurer as appropriate.
Check your body corporate rules and insurance policy, and take advice from your lawyer or body corporate manager before acting on anything in this article.
