Words by Jason Bennett, Indoor Air Quality expert at Zehnder Group UK
With stricter energy regulations and rising insulation standards, architects are understandably designing homes to be airtight and therefore more energy-efficient.
Building regulations Approved Document Part L (Conservation of Fuel and Power) sets the bar for energy efficiency in buildings. However, in our determined drive to build airtight homes, it’s ctricial counterpart, Part F (Means of Ventilation), is often unintentionally overlooked. But without effective airflow, these well-sealed homes trap moisture from everyday activities leading to the development of condensation, mould growth and poor indoor air quality.
Condensation & Mould in Airtight Homes
Condensation occurs when warm, moisture-laden air comes into contact with a cold surface, turning water vapour into liquid.
For the building itself, condensation can be a serious structural threat. Persistent dampness on walls and ceilings, particularly during the colder months, can not only damage interior finishes, but the prolonged accumulation of moisture can also lead to the decay of a building’s materials. Over time, this damage can weaken structural components, resulting in costly repairs, and even risk the safety of the building itself.
However, there is another layer to this problem. The moisture caused by condensation also affects insulation. When damp, the materials lose their ability to retain heat effectively, undermining their role of insulating for thermal efficiency. This ongoing battle between warm indoor air and cold external surfaces leads to increased energy demands for heating, driving up energy costs and putting more strain on a building’s HVAC system.
For architects, this presents a significant challenge. Balancing airtightness with effective ventilation requires careful material selection and advanced modelling to calculate suffient flow rates and air changes per hour. The risk of long-term building performance issues and increased operational costs makes this an unsustainable burden for architects who are aiming to meet energy-efficiency and carbon-reduction targets.
But the most concerning issue is the build-up of mould and mildew as a result of condensation. Routine activities such as boiling the kettle, cooking, bathing and showering can produce significant amounts of water vapor – up to 24 pints per day for the average family. Without effective ventilation to manage this moisture, damp conditions become the perfect breeding ground for mould and mildew which release spores into the air.
This can pose significant health risks to residents – exacerbating allergies, causing asthma complications and other respiratory conditions and in serious cases even death, especially in children and the elderly.
A Balanced Approach to Heating and Ventilation
The good news is that condensation doesn’t have to be an inevitable problem. The solution lies in achieving the optimal balance of heating and ventilation throughout the home, and this can be done at the building design phase. Architects must consider these elements from the outset to create homes that are not only energy-efficient but also healthy and sustainable.
The first is a simple yet continuous air system comprising of trickle vents on windows and dMEV extract fans with humidity boost in wet rooms throughout the home. Trickle vents are designed to work harmoniously with extractor fans, forming an effective whole-home ventilation system. By allowing a continuous flow of fresh air into a property, these vents work in tandem with the extractor fans, which efficiently remove the stale, moisture-laden air.
New fans on the market, like the Zehnder Unity CV2.1HT, run constantly with an integrated humidity sensor to give a boost, or more demand ventilation when it is needed, such as after showering or while drying clothes. They are whisper quiet and run at a minimal cost – less than £2 per year. This intelligent air flow system not only enhances indoor air quality but also helps prevent condensation and mould, ensuring a healthier living environment for occupants.
The second option to protect homes against this build-up of poor indoor air quality is a mechanical ventilation system with heat recovery (MVHR). With an MVHR ventilation system stale air is extracted but before leaving the house, the air passes over a heat exchange which recovers the heat that would otherwise be lost outside. A warm, filtered fresh air supply is then fed back into the property. MVHR systems provide ventilation with heat recovery of up to 96%, which can reduce the load on heating systems.
Then in the summer months when cooler air is required, the MVHR activates its modulating bypass to prioritise the recovery of the cooler air through the system. This provides a comfortable climate all year round as well as clean, fresh, filtered air for better occupant health and wellbeing.
While ventilation plays a crucial role in reducing moisture build-up, it is only half the solution. Temperature regulation is just as important and the challenge for architects is to design heating systems that ensure consistent thermal distribution.
The placement of radiators should be specified for optimal thermal output around the home – utilising wall space effectively to avoid them being blocked by furniture or not heating rooms where it is needed most. Radiators can now be hung vertically as well as horizontally to free up wall space, while still providing heat to potential cold spots where condensation could form, and mould develop.
Designing for the future
Meeting the standards set out in building regulations isn’t enough. Ventilation and heating requirements should be specified to the needs and living behaviours of the home. It is not a case of one size fits all, and how we design and build our homes is key to the ultimate health and wellbeing of those that will live in them.
Architects have a responsibility to look beyond the minimum standards and design homes that actively support the health and well-being of their occupants. Homes of the future will see systems working together as one, adopting climate strategies for the property that fundamentally change the layout of a building to assist with how we live in it.
By taking a proactive approach to ventilation and heating, architects can lead us to a new standard of building design which moves beyond quick-fix solutions. The goal shouldn’t just be energy efficiency, but to create homes that also preserve structural integrity and support human health.