Why is my home so humid?
Indoor humidity rises when moisture is added faster than it is removed. Everyday life adds several litres of water to the air each day — cooking, showering, drying laundry, even breathing. In a home with good ventilation, that moisture is carried away and humidity stays comfortable. In a home where ventilation is poor or the building has become more airtight without a ventilation upgrade, the moisture accumulates. Once relative humidity climbs above about 60%, mould thrives and the home feels clammy.
High humidity is the common thread behind condensation, mould and that persistent musty smell. Rather than treating each symptom separately, a humidity investigation tackles the root: too much moisture, too little ventilation, and surfaces cold enough to condense it.
Where the moisture comes from
Identifying the sources is half the solution. Kitchens and bathrooms are the biggest generators, especially without effective extract. Drying laundry indoors releases litres of water directly into the air. Unvented tumble dryers, aquariums and even a large number of houseplants contribute. And in some homes, an underlying damp problem adds moisture from the structure itself. We help you see which sources matter most in your home.
Why the moisture isn't leaving
The other half is ventilation. Extract fans that are underpowered, poorly sited or simply not used; trickle vents that are closed or absent; and homes made airtight by new windows and draught-proofing without a matching ventilation strategy — all leave moisture with nowhere to go. The aim is not to make the home draughty again, but to remove moist air deliberately and efficiently. We assess how your home ventilates and where it falls short.
How Retrofit IQ investigates high humidity
We measure relative humidity, temperature and moisture across the home, not with a single spot reading. Dew-point analysis shows how close your air is to condensing. We review the ventilation provision room by room, and use thermal imaging to find the cold surfaces where high humidity turns into condensation and mould. Where relevant we test airtightness. You receive a clear picture of your moisture balance and a prioritised plan to correct it.
Part of a full Building Performance Investigation
Humidity, ventilation, insulation and air leakage are all connected. A high humidity investigation is most valuable as part of a full Building Performance Investigation, which ties them into one prioritised plan — the reliable way to a comfortable, healthy indoor climate.
Why humidity problems cluster in winter
High humidity is usually most troublesome in the colder months, and understanding why helps make sense of the problem. In winter, windows and doors stay closed, so less moisture escapes; surfaces are colder, so the air reaches its dew point more easily; and heating drives more moisture-generating activity indoors. The result is that the same household habits produce far worse symptoms in January than in July. If your damp, clammy feeling and mould appear or worsen with the cold, it points firmly at the combination of trapped moisture and cold surfaces that our investigation measures.
New-builds and airtight retrofits
Modern, airtight homes and recently retrofitted properties are surprisingly prone to humidity problems. The very airtightness that saves energy also removes the accidental ventilation older homes relied on, so moisture accumulates unless a proper ventilation strategy is in place. This is why so many owners of new or upgraded homes are puzzled to find condensation and a clammy feel in a property that should be efficient and comfortable. The solution is not to make the home leaky again, but to add the controlled ventilation it needs — which the assessment identifies.
Monitoring your humidity
A simple, inexpensive hygrometer is a useful ally in understanding a humidity problem. Placed in the rooms that concern you, it shows how relative humidity rises and falls through the day and in response to cooking, showering and drying laundry. Seeing the numbers climb after particular activities makes the moisture sources obvious and shows whether ventilation is coping. Our investigation goes further with calibrated measurement and dew-point analysis, but ongoing monitoring afterwards is a good way to confirm that improvements are keeping humidity in the healthy range.
Humidity, comfort and heating
Humidity affects how warm a home feels and how much it costs to heat. Damp air feels colder and takes more energy to warm than dry air, so a humid home can feel chilly even when the thermostat is up — tempting you to burn more energy chasing comfort. Bringing humidity into a healthy range makes the same temperature feel warmer and more pleasant, and reduces the condensation that damages finishes. Comfort, health and running costs all improve together when the moisture balance is right, which is the outcome the investigation is designed to deliver.
What you receive
The health effects of living with high humidity
Persistently high humidity does more than make a home feel clammy. It creates the conditions for mould, which can affect respiratory health, and it encourages house dust mites, a common trigger for asthma and allergies. Damp, humid air is also linked to poorer sleep and general discomfort. For households with children, older people or anyone with a respiratory condition, bringing humidity back into a healthy range is not just about protecting the building — it is about protecting the people in it. This is why we treat humidity as a health issue as much as a building one.
Humidity, dust mites and allergens
House dust mites thrive in humid conditions and struggle when relative humidity is kept below about 50 per cent. For allergy and asthma sufferers, controlling indoor humidity is one of the most effective environmental measures available, reducing the mite population and the allergens they produce. High humidity also keeps mould spores in circulation. Measuring and managing humidity therefore has benefits that reach well beyond condensation on the windows — which is why our investigation quantifies it precisely rather than relying on how the air feels.
Practical moisture control, room by room
Because moisture is generated in specific places, control starts there. Kitchens need effective extract during and after cooking, and lids on pans. Bathrooms need extract that runs long enough to clear the moisture from a shower, not just while someone is in the room. Laundry should ideally be dried outside or in a ventilated space rather than on radiators, which release litres of water into the air. Our investigation identifies which sources matter most in your home and pairs source control with the right ventilation, so you are not fighting a losing battle against moisture you keep generating.
Why a whole-home approach beats a dehumidifier
A dehumidifier can take the edge off a humidity problem, but it treats the symptom and runs up an electricity bill doing so. It does nothing about the moisture sources, the ventilation gaps or the cold surfaces where condensation forms. A whole-home approach — reducing moisture at source, ventilating deliberately and warming the cold surfaces — addresses the causes together, so humidity stays in a healthy range without a machine running in the corner. The investigation is what reveals the right combination of measures for your specific home.
- Measured humidity, temperature and dew-point findings
- Identified moisture sources in your home
- A room-by-room ventilation assessment
- Thermal images of the surfaces where condensation forms
- A prioritised plan to bring humidity into a healthy range
A real-world investigation example
A homeowner whose home felt persistently clammy, with steamed-up windows and mould appearing in several rooms, was surprised to measure relative humidity consistently above 65 per cent. Monitoring showed it spiking sharply whenever laundry was dried on radiators and after showers, while the bathroom extract fan was too weak to clear the moisture and several trickle vents had been painted shut. The moisture was being generated faster than the home could remove it. Drying laundry in a ventilated space, upgrading the extract and reopening the background ventilation brought humidity down into the healthy 40–60 per cent range, and the mould stopped spreading.
Common homeowner mistakes
A common mistake is running a dehumidifier continuously and treating that as the solution, paying to remove moisture while the sources and ventilation gaps remain. Another is drying washing on radiators indoors, which releases litres of water into the air, then wondering why the home is damp. Homeowners frequently close trickle vents and seal draughts for warmth, removing the very ventilation that keeps humidity in check. And addressing mould room by room, rather than the whole-home moisture balance driving it, means it simply reappears somewhere else.