The Silent Menace: Tackling Condensation and Mould in Housing through Effective Ventilation Strategies

By Mark Trowers, indoor climate specialist at Zehnder Group UK

Condensation – the often-overlooked adversary in homes that silently creeps into spaces, leaving behind a trail of consequences that can significantly impact the structural integrity, occupant health, and overall efficiency of a property. 

Despite its seemingly innocuous nature, condensation is a pervasive issue that demands attention and proactive measures within the realm of building management.

No building is immune. Older buildings that are not insulated are most at risk but also newer buildings with inadequate airflow can be vulnerable as we seek to better insulate for net zero gains. 

In our efforts to insulate better and make our homes airtight for better energy efficiency many fail to understand the impact it has on indoor air quality. When the property is not able to breathe, stale air and excess moisture get trapped inside creating a sick environment. Effective ventilation is key for keeping homes healthy. 

Condensation occurs when warm, moisture-laden air comes into contact with a cold surface, causing the water vapor to transform into liquid water. It is especially prevalent in homes due to temperature differentials between indoor and outdoor environments, as well as variations within the building itself. Without effective ventilation, the airflow is restricted and humidity build-up exasperates the problem. 

Condensation on its own, shouldn’t be cause for alarm – although can prove an irritant and lead to financial implications. However, where condensation forms on ceilings and walls in colder conditions, the drips can lead to damage of internal finishes as well as affect the health and wellbeing of the residents. What is more alarming, if left alone, condensation can lead to damp and turn into black mould which is toxic to humans.

As highlighted in the Housing Health and Safety Rating System (HHSRS), mould can lead to various health issues for those who spend time in damp and mould affected properties. These health effects can include breathing difficulties, depression and anxiety, and asthma. 

What may initially seem like minor symptoms, such as a blocked nose, sore throat, or itchy skin, can often be mistaken for the common cold, especially in winter. In extreme cases mould can cause severe health issues and even death. For example, a 2022 study by the University of Birmingham found that exposure to mould in buildings was associated with an increased risk of asthma attacks, especially in children.

Building damage and poor indoor air quality

One of the primary concerns associated with condensation is its potential to compromise structural integrity. Moisture accumulation can lead to the decay of building materials, promoting the growth of mould and mildew. Over time, this can weaken the structural components, resulting in expensive repairs and jeopardising the safety of the house. Regular inspections and maintenance are crucial to identifying and addressing these issues before they escalate.

Condensation not only affects the building’s physical structure but also has a direct impact on indoor air quality. We know that the average family produces 24 pints of water vapour a day through routine activity, such as boiling the kettle, cooking, bathing and showering, even breathing! Without extraction, that moisture can build up and find the coldest surface in the house, producing condensation.  

The damp environments created by condensation provide an ideal breeding ground for mould and mildew, releasing spores into the air. Inhalation of these airborne contaminants can lead to respiratory issues, allergies, and other health concerns among building occupants and without effective means to ventilate the building and reduce the humidity in the air, the problem grows or keeps returning. 

It isn’t just health and structural concerns that we need to consider, however. Condensation-induced moisture can also compromise the effectiveness of insulation materials, reducing their thermal resistance and contributing to uncomfortable indoor temperatures. 

This constant battle between warm indoor air and cold exterior surfaces necessitates increased heating or cooling efforts to maintain a comfortable temperature within the building. It is this heightened demand for energy that not only strains HVAC systems but also translates into higher energy costs for the property.

Mitigating the impact

Addressing condensation in social and rented housing requires a multi-faceted approach. Investing in proper insulation and effective ventilation systems can help regulate indoor humidity levels, minimising the conditions conducive to condensation. Routine inspections and maintenance are essential to identify and rectify potential issues before they escalate, safeguarding the structural integrity of the building.

In some cases, a building will have a ventilation system that should work for the building it serves, yet condensation problems still arise. This could mean that the system needs to be reviewed or checked or was installed incorrectly to being with. No ventilation system, inspected and installed correctly by a competent M&E contractor, should have humidity build up to that degree.

Alternatively, if a property is a multi-purpose space or has seen alterations in its layout, be it through expansion or refurbishment, this complexity is further compounded. What may have once constituted an effective method of air circulation during the initial construction may no longer prove suitable. For example, when a house is converted into multiple flats or apartments. 

Adjusting the ventilation system to address these modifications isn’t always a feasible option and, in these cases, systems will need renewed consultation to assess the requirement and maintenance going forward.

A ventilation system, be it mechanical ventilation with heat recovery (MVHR systems) or extract fans and cooker hood extraction, must also be serviced properly to ensure it functions as intended. Regular maintenance of these systems is crucial – such as changing filters and ensuring extract fans are clean and in operation.

Condensation, though often overshadowed by more overt building issues, poses a substantial threat to the structural integrity, residents’ health, and energy efficiency of properties. Acknowledging its presence and implementing proactive measures are paramount to mitigating its impact. 

Addressing condensation is not just a matter of maintenance and blaming tenant behaviours – although education for tenants is an important part of it; it’s a strategic investment in the longevity and performance of housing structures and people’s health.