How properties are built, refurbished and maintained has evolved over time in response to changes in technology, product innovation, aesthetic trends, the climate emergency, material availability, and policies and standards. Buildings, including homes, are now increasingly airtight, which can result in condensation, mould and poor indoor air quality due to insufficient ventilation.
Previously, it was commonplace to open a window and perhaps use a cooker hood or bathroom fan, operated by a light switch if there was no window, to ventilate a property. This was usually sufficient for older housing stock, which tends to be draughty with many leakage gaps around windows, doors, letterboxes, air bricks and chimneys, as there was enough background air leakage alongside these ventilation solutions.
Homes are now being built to a higher level of air tightness, as required by Building Regulations Part L, meaning traditional ventilation methods are not always sufficient. Approved Document F now requires additional measures, including a high number of trickle vents in windows, which is seemingly counterintuitive when every effort has been made to reduce any leakage. Mechanical ventilation solutions are increasingly required as the air tightness levels mean that natural options may no longer be feasible.
Did you know?
An average family home creates sixteen pints of moisture a day, from general everyday activities.
But where does all this moisture go? Without the correct ventilation in a modern home, this will lead to higher humidity and moisture levels, which are unable to escape, creating condensation, which then leads to dampness, mould, and overall poor indoor air quality.
Air tightness, or how ‘leaky’ a building is, is generally measured using a door blower test or a pulse test.
The door blower test involves using a large fan that covers a doorway. All windows, air bricks, loft hatches, etc., are closed or sealed before the fan is powered. The fan forces air into the building and records how much additional air is required to maintain the air pressure. This enables the level of air leakage to be measured. Any leakage points can be identified and rectified if necessary.
The pulse test involves using specialist equipment that is pressurised up to a set level in line with the volume of the building envelope. Once this is complete, one or more pulses of air are released into the building, creating a pressure difference between the interior and exterior of the building.
With both measurement options, once the data has been retrieved and an air permeability level measured, appropriate remedies can be undertaken (if required) to meet the level required by the building designer or contractor to show compliance with the Building Regulations.
Things to consider:
- If a property is significantly airtight, what happens to any pollutants from things like deodorants, candles, paints, carpet fibres or glues used to seal furniture? Whilst a window could be opened to assist with the removal of these contaminants, it may not be practical due to poor weather, noise, safety and external pollution.
- Poor indoor air quality can lead to health issues, mould and condensation and affect the fabric of the building.
- Condensation and mould are key areas of concern when it comes to determining the breathability of a building. Condensation is formed when warm, humid air meets colder surfaces such as windows and exterior walls or ceilings. With good ventilation levels, temperatures can be evened out, providing a better mixture of air and better control of moisture, and therefore reducing the levels of condensation. The use of suitable ventilation and mitigation against this, alongside the sufficient heating of the area, will prevent mould formation.
- Mechanical ventilation should be used alongside either reduced or zero-trickle ventilators. When using an MEV or Mechanical Extract Ventilation unit, the background ventilation requirement is significantly reduced compared to intermittent on/off extractors. For the use of MVHR or Mechanical Ventilation with Heat Recovery, there is no requirement for background ventilation as the system also supplies filtered air and extracts the stale, moist air from wet rooms.
- What options are available if an internal ducting layout or route isn’t suitable for the property? Those intermittent fans can be upgraded to Decentralised Mechanical Extract Fans, commonly known as d-MEV. These are usually 100mm in size, similar to the older fans and provide a continuous method of ventilation.
How would you know if the air in a building is poor?
Sensors are available that can be used in conjunction with ventilation systems, allowing an indication of Volatile Organic Compounds (VOCs) such those found in glues and carpet fibres. CO2, temperature and RH (Relative Humidity) sensors are also available depending upon the needs and requirements of the building.
The effect of not having good-quality air in a home is dramatic. The average person spends 90% of their time indoors, and 70% of this time is spent in their own home. The indoor living environment is therefore crucial to the health of the occupants.
With modern homes being constructed to more airtight methods because of material usage, off-site construction and carbon reduction, the importance of suitable ventilation for dwellings with improved insulation, glazing, and other energy saving measures has never been more important to allow for a healthy home.
The right ventilation solution for the property should be determined using the Approved Documents, layout, occupancy and general living variables such as the number of pets, heating schedules, any pollution or acoustic issues and overheating concerns.
Once this has been determined, a competent, knowledgeable installer should be chosen to fit the system. This could range from a whole house MVHR system to an improvement of the extractor fans from intermittent to continuously running d-MEV fans.
Types of Ventilation Solutions
- Positive Input Ventilation (PIV) is a whole-house air ventilation system that works by drawing filtered air into a property from outside. PIV systems help create a healthy living environment by supplying filtered air centrally into a property, diluting and displacing indoor contaminants.
- Intermittent extract fans work in conjunction with natural ventilation and background ventilators (trickle vents) and are a functional and practical solution for controlling excess humidity, or unwanted odours. On a basic level, any extractor fan draws out the moisture at source which creates a negative pressure in the dwelling, allowing the extracted moisture laden air to be replaced by external air.
- Mechanical Extract Ventilation (MEV) systems can be either whole-house centralised units or decentralised fans. The centralised MEV systems are typically in a loft or hallway cupboard. Multiple ducts run from the unit to the kitchen, bathroom, en-suites, and other wet rooms of a property to simultaneously draw moisture-laden air from these wet rooms to control humidity levels. Decentralised systems continuously run extract fans in each individual wet room. Continuous running extract ventilation is more controlled and energy-efficient to ventilate a dwelling than a traditional on/off fan.
- Mechanical Ventilation with Heat Recovery (MVHR) systems are sophisticated whole-house ventilation and condensation control units. The systems work by extracting stale, moisture-laden air from the wet rooms such as bathrooms, which passes over a high-efficiency heat exchange cell before reaching the atmosphere. Simultaneously, filtered air is drawn into the unit from outside and is warmed by the heat exchange cell before being delivered through supply vents into the living, dining, and bedroom areas. Systems typically recover 85-95% of the heat being extracted, reducing the heating demand for the dwelling.
Ventilation is considered a controlled service and should be specified and installed by persons competent to do so.
There are Competent Persons Schemes for mechanical ventilation installers, such as the NICEIC, which offers training courses like the Domestic Ventilation Course.
Using an installer who is a member of a Competent Persons Scheme will ensure that the right solution is designed, installed, commissioned and certified.
Use this postcode search to find a competent person in your area.
The NHIC wishes to thank WG2 | Consumer Voice members for contributing to this guide.
Please note that this guidance document produced by the NHIC was correct when created. However, information and regulations may have changed since its publication. Therefore, seeking the most up-to-date information and expert advice is always advisable before making any decisions related to improving your home.
