What are signs of poor ventilation in a home? This checklist answers it room by room, from Jordan Statham, director of The Conduction Company and a registered electrician and electrical inspector who assesses Auckland homes for ventilation. It covers where to look, what each sign means, and what gets fixed first. For condensation itself, The Conduction Company has a separate guide to the causes of condensation and how to stop it .
The Conduction Company reads poor ventilation from a musty, damp smell as you walk in, mould or a damp sheen on ceilings, wet windows in the morning, and mould on clothes in wardrobes. Bathrooms show it first, then laundries and bedrooms. The most common cause is moisture with no extraction to remove it at the source.
How do I know if my house has poor ventilation?
The Conduction Company can usually tell as soon as it walks in: a badly ventilated house smells musty and damp, and you can feel the damp straight away.
Condensation on the windows in the morning is a clear sign, but it is not the only one. Look for mildew and mould building up anywhere in the house, mould spots on the ceilings, and a sheen on a ceiling that shows moisture is present. Bathrooms with poor extraction are the usual place to see it.
"For us as installers and assessors walking into a home, we can tell straight away, just with the odour of a property, whether or not they have a moisture issue," says Jordan Statham, director of The Conduction Company.
It is common. The 2023 Census found 20.1% of Auckland homes were damp at least some of the time, and 17.4% had mould larger than an A4 sheet (Knowledge Auckland, March 2025).
What does a badly ventilated house smell like?
Musty and damp. Jordan Statham of The Conduction Company says the smell is a combination of three things. A damp, slightly warm house is the perfect breeding ground for bacteria, and the gas they give off causes the odour. Mould and mildew each add their own distinctive smell on top.
The catch is that the people who live there get used to it and may stop noticing it. Someone who does not live there, like an assessor walking in, notices it at once.
What are the signs of poor ventilation room by room?
Mould shows up first where the moisture is made. Here is where The Conduction Company looks in a house, and what each sign means.
What are the signs of poor ventilation in a bathroom?
Mould is the sign, and The Conduction Company finds it in the bathroom first in most homes, unless the bathroom has an extractor fan.
Look for mould spots and a damp sheen on the ceiling. An extractor fan is a form of ventilation: it is negative pressure ventilation, pulling the wet air out. A bathroom without one is usually where the mould shows up first.
What are the signs of poor ventilation in a laundry?
Mould in a laundry usually means the moisture from washing has nowhere to go. The Conduction Company sees it most where the dryer is not ducted to the outside, or where clothes dry on a rack in a laundry with no extractor. Both are a high-moisture situation.
What are the signs of poor ventilation in a bedroom?
Moisture on the ceiling is the sign, and The Conduction Company finds it in bedrooms because the people sleeping there breathe moisture into the air all night.
With no proper ventilation, that moisture from breathing in and out settles on the ceiling, which is a breeding ground for mould and mildew. Two people in a smaller room double the amount of moisture being produced.
What do you find in wardrobes and behind furniture?
Mould and mildew patches on clothes, shoes and the backs of couches. The Conduction Company finds wardrobes especially bad, because there is zero air movement and only one way in and out, so the air stays damp.
Clothing holds moisture, and the mould can ruin it, leather in particular. Shoes collect mould too, and so do the backs of couches, where there is limited air movement. Fabrics and textiles hold moisture, so drier air around them pulls the moisture back out and reduces the mould and mildew.
What do you find in the roof space?
Usually warm, dry air. In the vast majority of homes The Conduction Company works in, no moisture is produced in the roof space, so it is significantly warmer and drier than the house below. That is where a positive pressure ventilation system draws its air from.
Older homes with gable-end passive ventilation tend to stay very dry up there, because the roof space ventilates naturally. Age is not a reliable guide, though. Some really modern homes, especially those with tin roofs, get heavy condensation forming on the tin roof and leaking into the ceiling void. Some roof spaces are also quite dirty from years of dust and debris.
How to tell if the air in your house is making you sick?
The pattern clients describe to The Conduction Company is a household that keeps getting sick in a damp house, and the people who complain most are usually those prone to asthma and respiratory illness.
We have been in homes with very high moisture and an overcrowded family, where the owners told us their children were continuously sick and they did not really know why. Jordan Statham's read of those homes is simple: too much moisture and too many people breathing in it.
In some of those homes, The Conduction Company has installed a ventilation system and got it working properly. After a couple of weeks the home is significantly drier. When we go back a couple of months later, clients tell us it is the best thing they have ever done, and that their children are no longer getting sick, or nowhere near as sick, especially during winter.
It is not only moisture. In a house that is shut up in mid-winter with the windows closed, everything you put into the air by cooking, breathing and living there stays put, because it has nowhere to go.
If someone in your home is unwell, see your GP. The Conduction Company can tell you whether the house is damp.
How do you test your house for air quality?
The Conduction Company tests a house for damp air mostly by walking through it: the smell tells you straight away whether a place has a moisture problem, and there is no particular two-minute test beyond that.
Sometimes we use a humidity sensor to get more granular. It compares the relative humidity inside with the reading outside. If the number drops off sharply once you step outside, the house is holding more moisture than the outdoor air is carrying, and that points to a moisture problem. Jordan Statham says the meter rarely tells The Conduction Company much more than the symptoms people describe.
Why can a well-kept home still be badly ventilated?
Because the family is doing the ventilation by hand. The Conduction Company has been into homes with a real humidity problem that felt relatively dry on the way in, because the people living there were expertly managing it.
Once we worked out how the family was operating, the routine gave it away: vacuuming the condensation off the windows every morning, dehumidifiers in pretty much every room, and the windows open in winter, freezing themselves just to get some airflow. Other families clean the mould off the ceilings every other week. You can still smell the damp when you walk in. They are keeping on top of it, but it is a daily task, worst in mid-winter.
A ventilation system operates completely automatically, and Jordan's view is that it can resolve all of that. "You can get all of that time back, and you can relegate the window vacuum to the cupboard where it belongs," says Jordan Statham of The Conduction Company.
Which Auckland house types are worst for poor ventilation?
Old and shaded homes are the worst culprits for humidity problems, in The Conduction Company's experience across Auckland.
That means older homes that have not had much work done on them, colder homes, homes that are locked up tight, and homes with more people living in them, because overcrowding makes a huge difference. Homes blocked from the sun are badly affected too. In areas like Titirangi and Huia, a lot of homes are surrounded by bush. The air around them is damp air off the bush, and they are constantly shaded, so they miss the drying effect of the sun that other homes get.
What is the most common cause of poor indoor air quality?
A lack of extraction, says The Conduction Company, along with drying clothes inside.
Clothes hold a lot of water after washing, even after a spin cycle. Hang them on a rack inside, or put them in a dryer that is not ducted to the outside, and all of that moisture goes back into the house. It is the same moisture that appears on your windows in the morning. Showers and other wet areas without adequate extraction do the same. With no way to force the moisture out and push fresh air in, the house becomes a high-humidity environment.
What do people try first that does not work?
A dehumidifier, says Jordan Statham of The Conduction Company. Dehumidifiers do work, but they are a very energy-intensive way to pull humidity from the air, and they only work in the spot where they sit.
Put one in a laundry where you dry your clothes with no extraction, and the moisture comes off the clothes, then you spend a significant amount of energy pulling it back out of the air into the dehumidifier's drip container. It is an inefficient and expensive way to reduce the moisture in a home.
How do you fix poor ventilation in a house?
The Conduction Company fixes extraction first, in every case: a rangehood in the kitchen, and extractor fans in the bathrooms and laundry, because it is much easier and more efficient to remove moisture at its source.
Extracting from the wet areas makes an enormous difference, especially in a laundry where the dryer is not ducted to the outside. In some homes that turns out to be the main reason for the mould and mildew: many washing loads a day, and the moisture from every load pushed back into the house.
At the same time, we look at positive pressure ventilation. It pushes fresh, warm, dry air into the dry rooms of the house, while the extractor fans pull wet air out of the wet rooms. That push and pull creates a continuous path of air through every room, which The Conduction Company has found is the best way to ventilate a whole home. If you are choosing a system, The Conduction Company compares HRV, DVS and SmartVent home ventilation systems in a separate guide, and sets out what a home ventilation system costs in NZ in another.
In short
A badly ventilated home gives itself away by its musty, damp smell, mould or a damp sheen on the ceilings, and mould on clothes and shoes in wardrobes. Bathrooms usually show it first, then laundries and bedrooms, and old or shaded homes are the worst affected. The most common cause is a lack of extraction, often with clothes dried inside, so extraction is the first thing The Conduction Company fixes, alongside positive pressure ventilation. That checklist comes from Jordan Statham's own assessments of Auckland homes, in his words above.
If your home has these signs, The Conduction Company offers home ventilation assessments and installation across Auckland . Happy to help.
Frequently asked questions
What are the symptoms of poor air quality in a house?
The symptoms The Conduction Company sees most are a musty, damp smell, mould or a damp sheen on the ceilings, wet windows in the morning, and mould on clothes and shoes in wardrobes. Clients also describe a household that keeps getting sick in a damp house, most often those prone to asthma and respiratory illness.
What causes poor ventilation in a home?
In The Conduction Company's experience, the most common cause is a lack of extraction, often with clothes dried inside. Moisture from showers, laundries and people breathing has no way out, and with no fresh air pushed in, the house becomes a high-humidity environment.
What are the signs of poor ventilation in a house in winter?
Winter is when The Conduction Company sees the signs at their worst, because the house is shut up: condensation to vacuum off the windows every morning, mould to clean off the ceilings every other week, and families opening the windows and freezing just to get some airflow.
What are the effects of poor ventilation in a room?
The Conduction Company finds moisture settling on the ceiling, mould and mildew growing there, and stale, damp air that leaves mould and mildew patches on clothes, shoes and the backs of couches. In a bedroom, two people sleeping in a smaller room double the moisture being produced.
What are the risks of poor ventilation?
Clients tell The Conduction Company about children who are continuously sick in a damp, overcrowded house, and those prone to asthma and respiratory illness complain most. Mould can also ruin clothing, leather in particular, and keeping on top of it by hand becomes a daily task.
How do you fix poor ventilation in a bedroom?
The Conduction Company fixes extraction in the wet areas first, then adds positive pressure ventilation, which pushes fresh, warm, dry air into the dry rooms of the house, bedrooms included, while extractor fans pull the wet air out. That push and pull keeps air moving through every room.
Do tenants and owners describe the problem differently?
Yes, says The Conduction Company. Tenants are usually concerned about their health and the extra work of keeping on top of the damp. Owners are worried about protecting their investment and keeping their tenants happy. Two different lenses, but they are looking at the same problem.
