The fire was next door, or in the flat downstairs. Nothing in your home burned, but for days afterwards it smelled of smoke, and now there is a grey film on the window sills that you don't remember being there. Did the smoke get in, and if it did, how much? Fire and Emergency New Zealand attends around 5,000 structure fires a year, and fewer than two in three stay in the room where they started. Smoke doesn't respect property boundaries, and in terraced houses and apartments it very often reaches the neighbours.
How smoke gets from one home into another
Smoke from a fire is hot, under pressure, and full of fine particles. It pushes out through any gap it can find, and the particles settle wherever the air slows down and cools.
- Shared ceiling and roof spaces. In semi-detached houses and townhouses, the ceiling space is often continuous across the dividing wall, or only partly separated.
- Gaps around services. Pipes, cables and ducts pass through walls and floors, and the gaps around them are paths for smoke.
- Stairwells, corridors and lift shafts in apartment buildings, where hot smoke rises and spreads along each floor. In one recent Auckland apartment fire, sprinklers kept the fire to a single unit, but around 300 residents were evacuated because of smoke.
- Ventilation. Shared extract systems, heat transfer kits, range hoods and air conditioning can all draw smoke in and spread it through a home.
- Open windows and doors, and outdoor smoke drawn in through vents, especially for homes downwind of a large fire.
Signs that residue got in
- A smoke smell that returns on warm days, or is strongest inside cupboards and wardrobes
- A grey or black film on window sills, the tops of door frames and light fittings
- Dark lines along the edges of carpet, under doors and around vents, where air carrying particles has passed through
- Discolouration around smoke alarms, extractor fans and ceiling vents
None of these proves fire residue on its own. Ordinary household dust, cooking, candles and wood burners produce similar-looking deposits, which is exactly why a laboratory measurement helps.
Why a measurement matters here
When the fire was in someone else's property, the question of who pays for cleaning is often the first argument. Your insurer, the neighbour's insurer and the body corporate may all have a view on whether your home was affected, and a visual inspection of a room that looks fine rarely settles it. An independent laboratory result, taken before cleaning and compared against a room the smoke didn't reach, replaces opinions with a measurement. We can't tell you which policy responds, but we can tell you whether combustion residue in your home is within normal background or above it.
What a sensible testing plan looks like
- Sample before anything is cleaned. Wiping surfaces removes the evidence. Choose flat, undisturbed surfaces.
- Sample the side closest to the fire: the room against the shared wall, the ceiling below the affected unit, the hallway nearest the stairwell.
- Sample the path: near vents, doors and service penetrations where smoke would have come in.
- Sample a comparison: the furthest room in your home. For air samples, add an outdoor sample taken at the same time.
- Sample again after cleaning to show that residue is back to normal background.
Surface samples are clear tape lifts, and air samples are taken on spore-trap cassettes with a calibrated pump. Each surface sample is reported in counts per square millimetre, with ash, soot and char listed separately from ordinary dust and combined into a total that is read against published normal-background ranges. Air results are reported per cubic metre and compared with the reference sample. The fire residue testing page shows example result cards.
What the test won't do
Fire residue analysis counts particles by microscopy. It doesn't measure the smell, gases or chemical compounds, and it doesn't tell you what burned. If your concern is mainly the smell, read Smoke Smell in Your House After a Fire, which explains why the smell and the residue are different problems. If the building was built before 2000, check WorkSafe's asbestos guidance before any fire debris is disturbed.