ROTTERDAM, 9 January 2025 – A recent study commissioned by HG, a specialist cleaning product manufacturer, has revealed that nearly 89% of Dutch households have dealt with mould, with over three-quarters of cases occurring in the past year. Rotterdam residents face particular challenges due to the city’s housing diversity and coastal climate.

Study highlights mould prevalence and causes

The HG study, conducted among Dutch households aged 25 to 65, sheds light on the widespread nature of mould issues across the country. Poor ventilation and high humidity are identified as the primary causes, with 80% of respondents linking these factors to mould growth. However, fewer people recognise low indoor temperatures as a contributing factor, even though colder air retains less moisture, leading to increased condensation.

“January, as the coldest month of the year, is a prime time for mould formation,” says John Zentveld, a mould expert at HG. “During winter, people keep their windows and doors closed to retain heat, but this results in high humidity and condensation, creating ideal conditions for mould to thrive.”

Rotterdam’s housing and climate exacerbate mould problems

Rotterdam’s unique mix of housing types presents varied challenges for residents tackling mould. In older neighbourhoods such as Delfshaven, pre-war apartments often have limited ventilation and damp basements, making them more susceptible to mould. Modern high-rise flats in areas like Kop van Zuid, while better insulated, can trap humidity if windows are not regularly opened. Converted industrial spaces in Katendrecht, with their large open layouts and exposed materials, are prone to condensation on cold surfaces.

Rotterdam’s coastal climate further complicates matters. The city’s maritime location means higher humidity levels compared to inland areas, making homes more vulnerable to moisture build-up. Daily activities such as cooking and showering contribute an additional 10 to 15 litres of moisture to indoor air, which, without proper ventilation, can settle on walls and other surfaces.

Energy-saving habits contribute to mould formation

The study highlights how rising energy costs have influenced household behaviour, with many residents reducing heating and ventilation to save on energy bills. These changes, while practical, have unintentionally increased mould risks. The cold air and limited airflow during winter months create an environment where mould can grow quickly, particularly in Rotterdam’s older or poorly ventilated homes.

Despite widespread awareness of the health risks posed by mould—78% of respondents believe mould is somewhat or very harmful to health—nearly half delay addressing the problem for two weeks or longer after noticing its presence.

Solutions tailored to Rotterdam homes

To address mould issues, residents of Rotterdam are encouraged to take preventative measures based on their home type. For instance:

• In older buildings, like those in Delfshaven, focus on improving ventilation and addressing damp basements.
• In high-rise flats, such as those in Kop van Zuid, ensure vents remain open, and consider using dehumidifiers.
• In industrial-style homes, like those in Katendrecht, maintain consistent heating to prevent condensation on cold surfaces.

“Ventilation, heating, and airing out rooms are essential for tackling the root causes of mould,” says Zentveld. “Mould won’t disappear on its own; it thrives on moisture and oxygen, which are always present. Cleaning visible mould helps, but without addressing the cause, it will return.”

Directions: common mould-prone areas in Rotterdam

Inspect your home for mould in places such as:

• Behind curtains and furniture in poorly ventilated areas
• Bathrooms and kitchens with high humidity levels
• Basements and other cold, damp spaces