Natural ventilation is an integral part of home design. Sometimes referred to as passive ventilation, it can be as simple as opening a window. However, it can also be as complicated as passive stack ventilation. Irrespective of how it is created, ventilation is crucial to the indoor air quality and overall health of the home and its occupants. As such, the UK Building Regulations set out several barometers for natural ventilation in the home. Passivhaus standards also require a certain level of ventilation, all of which we will discuss in today’s article.

What is natural ventilation?

Natural ventilation is a method for promoting the flow of air through indoor spaces without the use of mechanical systems like fans or air conditioners. This type of ventilation relies on the natural forces of wind and buoyancy to circulate fresh air into a building and expel stale air out. The objective is to maintain a comfortable and healthy indoor environment by facilitating air movement, regulating temperature, and dissipating moisture and odours.

Passive ventilation involves leveraging architectural elements like windows, vents, and chimneys to allow air to move naturally through a building. There are no fans or mechanical systems; instead, the building is designed to facilitate the flow of air effectively.

Wind – When wind hits the surface of a building, it creates different pressure zones. Vents or openings on opposite sides of a room can facilitate airflow from a high-pressure zone to a low-pressure zone.

Buoyancy – Also known as the “stack effect,” buoyancy-driven ventilation occurs because hot air rises and cold air falls. Warmer, lighter air tends to move upward, creating a vacuum that draws cooler, denser air into the space.

Design Elements

1. Windows: Their placement, size, and type (awning, casement, slider, etc.) significantly affect ventilation.
2. Vents: Wall or roof vents can help facilitate airflow, especially in areas that are far from windows.
3. Chimneys and Flues: Primarily found in older buildings, these create an excellent channel for buoyancy-driven ventilation.
4. Orientation and Layout: The way a building is oriented can enhance or impede the effect of natural forces, affecting how well natural ventilation works.
5. Landscaping: Outdoor features like trees or shrubs can either channel wind towards openings or obstruct it. Even bodies of water can affect the microclimate around a building.

Certainly, the mechanisms of natural ventilation can largely be categorised into three main types. Single-sided ventilation involves air entering and exiting through openings on just one side of the room, often due to constraints in building design. Cross ventilation takes advantage of windows or openings on opposite sides of a space. The design allows air to flow freely from one side to the other. Finally, stack ventilation utilises the natural buoyancy of hot air rising to facilitate air movement. Vertical shafts or atriums are used to enhance this effect.

UK Building Regulations

The regulation of ventilation in the United Kingdom is primarily overseen through Approved Document F of the Building Regulations. This comprehensive document serves as a guideline for architects, builders, and contractors to ensure that new constructions or major renovations meet minimum standards for adequate ventilation.

Increasingly, new buildings are being designed to be airtight for energy efficiency. In such scenarios, Approved Document F places extra emphasis on ensuring adequate ventilation to offset the reduction in natural air leakage.

Categories of Ventilation

1. Background Ventilation: This refers to the continuous low-level ventilation that helps to maintain acceptable indoor air quality. Approved Document F specifies minimum air flow rates for different rooms, often measured in litres per second (l/s) per square meter of the room area. Trickle vents in windows or permanent openings in walls are commonly used for this purpose.
2. Purge Ventilation: Also known as “rapid” or “boost” ventilation, this is meant for quickly removing pollutants and odours, especially in bathrooms, kitchens, and utility rooms. The guidelines indicate that controllable openings like windows should have a combined area equivalent to at least 1/20th of the floor area of the room to facilitate purge ventilation.
3. Mechanical Ventilation: While our focus is on natural ventilation, it’s worth noting that the regulations also set out specific requirements for mechanical systems, particularly in spaces where natural ventilation is impractical. These systems must be energy-efficient and comply with noise constraints.

Specifics by Room Type

• Kitchens: Extractor fans or cooker hoods are recommended, with a minimum extraction rate specified.
• Bathrooms: Mechanical extract fans are often required, with different air change rates specified depending on whether it’s a shower room, a bathroom, or a lavatory.
• Utility Rooms: Specific air extraction rates are set, especially if the space contains appliances like washing machines or dryers that produce moisture.

Benefits of natural ventilation

Natural ventilation offers a range of benefits that go beyond merely conserving energy. Firstly, it’s highly energy-efficient, relying on natural forces like wind and temperature gradients rather than electricity-driven mechanical systems. This translates to reduced operational costs over the building’s lifecycle. This lowers both utility bills and maintenance expenses for heating, ventilation, and air conditioning (HVAC) systems.

Secondly, natural ventilation significantly improves indoor air quality by continually refreshing the indoor environment and removing pollutants. This leads to a healthier living space, mitigating issues such as condensation and mould growth. These are common in poorly ventilated buildings. Enhanced air quality can also alleviate symptoms related to respiratory conditions and contribute to overall well-being.

Lastly, there’s a psychological aspect to consider. The feeling of a breeze, the scent of outside air, and the subtle changes in temperature throughout the day can greatly improve occupants’ comfort and satisfaction levels. Studies have shown that naturally ventilated environments can boost productivity and even enhance cognitive function. This makes them ideal for settings ranging from homes to offices and educational institutions.

Thus, natural ventilation serves not just as an eco-friendly choice but as a holistic approach. It addresses economic, health, and psychological factors, enriching the quality of indoor life.

Ventilation and the Passivhaus standard

The Passivhaus standards originated in Germany but have gained international attention, including in the UK. This standard places rigorous requirements on energy efficiency and also on ventilation. For a building to be certified under Passivhaus, it must maintain an air change rate of approximately 0.3 to 0.5 air changes per hour under normal conditions, using highly efficient heat recovery ventilators.