How Building, Occupancy and Social Factors Drive Mould Growth

Mould Growth Is Rarely Down to Just One Cause

When mould appears in a property, the instinct is often to look for a single cause — a leaking pipe, a broken extractor fan, a tenant who doesn't open windows. But the reality, as established by leading research from UCL and BSRIA, is far more complex. Indoor mould growth is driven by three interconnected categories of determinants: building factors, occupancy factors and social factors.

Building Determinants

The physical characteristics of a building play a major role in its susceptibility to mould. Properties at higher risk typically include those that are undermaintained or neglected, with blocked drainage, cracked facades or damaged damp-proof courses. Poorly insulated buildings with thermal bridges and cold surfaces — such as single-glazed windows — create condensation points where mould readily grows. Construction defects, including unsealed joints around windows, can facilitate moisture ingress. And buildings that weren't properly dried out after construction or a leak remain at elevated risk long after the initial incident.

Occupancy Determinants

How a building is used has a profound impact on its moisture profile. A typical household generates between 1,000 and 2,800 litres of moisture per year through everyday activities like cooking, showering, breathing and drying laundry. Each occupant releases approximately one litre of moisture into the air daily just by breathing. When moisture generation outpaces moisture extraction — through inadequate ventilation, for example — the excess accumulates and creates conditions ideal for mould growth.

Overcrowding amplifies this problem significantly. The more people in a space, the more moisture is produced. The Housing Act 1985 sets overcrowding criteria for England and Wales, but many properties in practice exceed safe occupancy levels.

Social Determinants

This is the dimension that is too often overlooked. Age, mobility, socioeconomic status and employment circumstances all influence a building's tendency toward mould. Low-income households are disproportionately likely to occupy poor-quality, undermaintained housing where fuel poverty and overcrowding compound the problem.

As the BSRIA guide states plainly: indoor mould growth is just as much a social problem as it is a technical one, and will require the right social policies to eradicate. The long-standing stigmatisation of people living in mouldy homes has led to inaction and silenced those most affected — particularly in social housing.

The Determinants Are Interconnected

These three categories don't operate in isolation — they influence and amplify each other. A household unable to afford heating may keep windows shut in polluted areas, reducing ventilation. A building with no outdoor drying space forces residents to dry laundry indoors, adding moisture. A landlord who doesn't respond to disrepair complaints allows building conditions to deteriorate further.

Understanding this interplay is essential for any organisation serious about tackling mould. Surface-level fixes — wiping mould off walls without addressing root causes — are not solutions. At Mould UK, our comprehensive reporting examines building condition, moisture sources and occupancy context to give housing providers a complete picture and a clear path to remediation.