Natural ventilation: Enhance your home with fresh air

Natural ventilation is a time-tested practice that has evolved to meet the demands of modern living. By utilising wind pressure and thermal lift, it continuously renews indoor air, enhancing the quality of life across every room in your home.

Natural ventilation relies on two main driving forces: wind pressure and thermal buoyancy. These natural processes allow fresh air to enter and stale air to exit, ensuring constant and beneficial air renewal for your indoor environment.

• Wind pressure: When wind strikes a building’s facade, it creates pressure differences, pushing air into less pressurised areas and enabling a steady flow of fresh air.
• Thermal buoyancy: Warm air rises due to its lower density, escaping through upper openings like roof windows. This upward motion draws in cooler, fresher air from lower openings, facilitating constant renewal.

Maintaining good natural ventilation in your living space is crucial. Here are five reasons why:

1. Improved indoor air quality: Most pollutants in your home originate from within (1). Adequate ventilation helps reduce levels of pollutants such as volatile organic compounds (VOCs), allergens, carbon dioxide, and other contaminants that can build up in poorly ventilated spaces.
2. Prevention of excessive humidity: Damp buildings can lead to mould growth and increase the risk of allergies (2). Natural ventilation helps control humidity levels, preventing mould development and protecting the structural integrity of your home as well as the respiratory health of its inhabitants.
3. Reduction of odours: Natural ventilation removes stale air and replaces it with fresh air from outside. This process keeps your home fresh and significantly reduces lingering odours.
4. Improvement of thermal comfort: Ventilation plays a role in regulating indoor temperatures by bringing in cooler air from outside, particularly during warmer months. This helps improve comfort while reducing the need to overuse air conditioning.
5. Energy savings: Good ventilation reduces the dependency on air conditioning and heating by employing passive strategies to maintain thermal comfort. This can result in significant energy savings.
6. Lastly, a well-ventilated environment positively impacts mental well-being, reducing feelings of confinement and improving your overall mood.(3)

Here are five natural ventilation strategies to optimise airflow in your home.

The aim is to create living spaces that are well-ventilated while maintaining energy efficiency, as well as acoustic and thermal comfort.

These methods can be customised and combined to suit your home’s specific needs, taking into account factors such as climate, geographical location, building orientation, and the layout of your rooms.

Cross ventilation involves opening opposite sides of the building to allow air to flow directly through living spaces. This strategy takes advantage of differences in air pressure created by wind and thermal variations.

For this to work effectively:

• The building design should promote a clear pathway for airflow, avoiding internal obstructions that might hinder its passage.
• Architectural elements, such as sunbreakers, internal courtyards, or strategically positioned openings, can enhance airflow through rooms.

The success of cross ventilation greatly depends on the building’s orientation relative to prevailing winds and the efficiency of the openings in capturing and directing airflow.

Your windows, roof windows, and doors can be equipped with manual or automatic controls to adjust ventilation according to weather conditions and specific needs.

Unilateral ventilation occurs when ventilation is achieved through a single façade. This method is often used when cross ventilation isn’t feasible, such as in certain urban settings or due to building configurations.

This strategy relies on air entering and exiting through openings on the same side of the building. Although less effective in creating airflow, you can improve it by:

• Exploiting vertical pressure differences (the stack effect): Warm air rises and exits, drawing in cooler air from below. This works particularly well in tall buildings or urban apartments where cross ventilation is limited.
• Strategically placing openings to increase airflow within the space. For instance, incorporating architectural features to create air turbulence is effective in large, open rooms.

This method utilises temperature differences between the interior and exterior of the building to create vertical airflow.

Warm air, being lighter, rises toward upper openings such as roof windows, while fresh air enters through lower openings like ground-level windows or grilles. Roof windows play a vital role in this process, allowing accumulated warm air to escape and promoting the upward movement of air.

This strategy is particularly effective in areas with significant temperature differences between day and night. By opening lower-level openings during the cooler hours, you can pre-cool the building, reducing the need for air conditioning during the day.

Good to know: VELUX roof windows have a ventilation flap that allows for continuous airflow without fully opening the window, offering protection from the weather.

This technique harnesses the power of wind to generate air movement throughout the building. It is particularly effective when used in conjunction with ventilation towers or windbreaks, which increase air pressure on one side of the building and encourage airflow through the interior.

The efficiency of wind-driven ventilation depends on wind direction and speed, as well as the design and orientation of the building. When used for short periods at high ventilation rates, it can effectively remove moisture and odours.

Atriums or central courtyards act as light shafts and ventilation wells, serving as buffer zones between the outside and inside of a building.

Fresh air entering the atrium is exposed to sunlight, warming it and causing it to rise through convection. This upward movement creates a draft that extracts stale air from surrounding living spaces.

Atriums not only promote natural ventilation but also flood interiors with daylight, enhancing the overall atmosphere of the home.

While often linked to mechanical ventilation systems, double flow ventilation can be integrated passively in eco-friendly building designs.

This technique aims to recover heat from exhausted air to preheat incoming fresh air, without relying on mechanical systems. Instead, passive heat exchangers and smart architectural designs facilitate this process, supporting sustainable construction goals.

The energy and indoor climate visualisation tool developed by VELUX Group allows the ventilation rates achieved through natural aeration to be measured.

An experiment conducted in Berlin, Germany, evaluated ventilation rates achieved with different window configurations:

• Combined stack effect and cross ventilation: 5.0 to 6.5 ACH
• Stack effect alone: 4.5 to 6.0 ACH
• Cross ventilation alone: 2.5 to 5.5 ACH
• Single-sided ventilation: 1.5 to 2.5 ACH

These results show that combining the stack effect with cross ventilation achieves the highest air change rate per hour (ACH), with rates significantly higher than the standard background ventilation rate of 0.5 ACH. Larger opening areas further increase ACH values.

In the Air and Light House built by VELUX in Essonne, France, up to 20 ACH was measured during the summer of 2012 (4), demonstrating the potential of innovative building designs for optimising natural ventilation.

Note: ACH, or air changes per hour, measures the efficiency of an air filtration system by calculating how often the air inside a space is replaced per hour.

Roof windows offer numerous advantages for improving natural ventilation in a home. From thermal management to indoor air quality and light intake, they contribute to a healthier and more comfortable living environment.

Roof windows utilise the chimney effect, where warm air rises due to its lightness compared to cooler air outside. By opening a roof window, the warm air escapes, creating a vacuum that draws in fresh air through lower openings, such as wall windows. This constant natural airflow improves ventilation throughout the home.

When roof windows are paired with side openings, they amplify the efficiency of cross ventilation. Fresh air enters through side openings, flows across the living space, and exits through roof windows, creating a refreshing and cooling airflow.

Roof windows are effective for expelling excess moisture and pollutants such as carbon dioxide, VOCs, and allergens. Opening roof windows regularly - especially after moisture-generating activities like cooking or showering - maintains a healthier indoor environment.

Roof windows provide direct control over the ventilation of your home. You can open and close them to regulate airflow based on weather conditions or personal preferences. Many modern roof windows come equipped with rain sensors that close automatically during bad weather and allow smartphone control for added convenience.

Spaces under the roof can overheat quickly, especially during warm weather. Strategically placed roof windows allow hot air to escape, reducing overheating and improving thermal comfort. This reduces reliance on air conditioning, lowering energy costs and promoting sustainability.

In addition to promoting air circulation, roof windows bring in extra natural daylight, visually transforming interiors and reducing the need for artificial lighting.

Expert tip: Incorporating roof windows into a building's design improves indoor air quality, enhances occupant comfort, and boosts energy efficiency, aligning with sustainable construction principles.

The success of a natural ventilation system relies on a carefully considered design that is tailored to the specific climatic and architectural characteristics of each project. Below are three important elements to take into account when designing your building project:

The orientation of the building plays a critical role in determining the efficiency of natural ventilation.

By aligning the building with the prevailing wind directions, you can maximise opportunities for natural air renewal. This ensures that fresh air circulates through the space effectively, enhancing the overall indoor environment.

The choice and positioning of windows are fundamental to the effectiveness of natural ventilation. Properly placed windows, both in terms of height and orientation, can significantly enhance cross-ventilation and promote optimal air circulation within the building.

The careful selection of window types, combined with strategic placement, ensures that airflow is not obstructed and can move freely throughout the space.

Incorporating materials with high thermal mass into your building design can help moderate indoor temperature fluctuations. Materials such as concrete, brick, or stone absorb and store heat during the day and release it at night, creating a more stable and comfortable indoor climate. This not only improves the overall thermal comfort but also enhances the effectiveness of natural ventilation systems by reducing reliance on mechanical temperature control methods.

The adaptability of natural ventilation makes it an effective solution for a wide range of climatic conditions, providing custom-tailored approaches for various environments.

In temperate climates, natural ventilation benefits from daily and seasonal variations to maintain a comfortable indoor environment.

Cross-ventilation, combined with a technique known as night flushing, is particularly effective in these areas. By using cooler night temperatures to refresh living spaces, night flushing helps reduce the need for air conditioning systems, creating a sustainable and energy-efficient solution for maintaining indoor comfort.

The high heat and humidity characteristic of tropical climates present unique challenges for natural ventilation. One effective strategy in these regions is stack ventilation, which utilises the temperature differences between the interior and exterior of a building to create a vertical airflow. This technique helps to cool the indoor spaces efficiently.

Additionally, architectural designs that include features for shading and weather protection further enhance living conditions by reducing heat gain while maintaining adequate air circulation.

In cold climates, the main challenge is achieving sufficient ventilation without causing excessive heat loss.

Natural ventilation solutions in these areas often include the use of systems like Canadian wells or controlled ventilation systems. These methods preheat the incoming fresh air using heat recovery techniques, ensuring that indoor spaces remain warm while still benefiting from fresh air circulation.

By balancing air exchange with the conservation of thermal energy, these strategies create a comfortable and energy-efficient indoor environment even in the coldest conditions.

The theory behind natural ventilation becomes tangible through real-life examples that showcase its benefits across various types of buildings. Below are examples from residential applications that demonstrate the effectiveness of natural ventilation strategies.

Residential buildings can incorporate multiple solutions to optimise airflow and improve thermal comfort. Here are three key strategies:

Materials with high thermal inertia can absorb, store, and release heat over extended periods, helping to minimise temperature fluctuations throughout the day and between night and day.

• Concrete: This material is widely used in floors, walls, and ceilings. It absorbs heat during the hottest hours of the day and releases it when temperatures drop, stabilising indoor temperatures.
• Natural stone: Used in interior structures or walls, natural stone helps maintain stable indoor conditions by moderating temperature changes.
• Brick walls: Known for their strong thermal storage capacity, brick walls help keep indoor climates comfortable.
• Earth constructions: Materials such as adobe or rammed earth walls provide excellent thermal inertia, making them particularly suitable for climates with significant temperature differences between day and night.

Outdoor design elements can greatly influence natural ventilation and thermal comfort by modifying the microclimate around buildings and directing airflow.

• Vegetation: Trees, hedges, and climbing plants provide shade and reduce air temperatures around buildings. They can also act as windbreaks, limiting cold wind penetration in winter while allowing cooling breezes in summer.
• Pergolas and shade sails: These features create shaded areas that reduce direct solar gain on facades and roofs, while still permitting airflow around and through them.
• Green walls and roofs: Beyond offering insulation and supporting biodiversity, green walls and roofs cool the surrounding air and improve the indoor thermal environment.
• Water features: Elements like water basins and fountains lower nearby air temperatures through evaporation, contributing to a more comfortable microclimate.

Integrating ventilation strategies at the design stage ensures improved comfort for occupants while reducing energy consumption. This proactive approach also helps prevent common issues found in homes lacking proper ventilation, such as humidity, mould, and unpleasant odours.

Commercial buildings, with their large spaces and high occupancy levels, face unique challenges when it comes to ventilation. A key question arises: how can we ensure optimal indoor air quality while minimising the energy costs associated with heating, air conditioning, and mechanical ventilation systems?

Educational establishments often face limited space per student in classrooms, leading to increased risks of high CO2 concentrations.

Good indoor air quality is essential for the concentration and well-being of students and staff. A study by the University of Salford (5) demonstrated a clear link between well-designed environments, air quality, and academic performance in reading, writing, and mathematics. Simply put, a well-ventilated, bright room fosters better academic outcomes.

For effective natural ventilation in schools, the proportion of the window opening area in relation to the number of students and the floor space plays a crucial role. (6)

Maximising the use of window openings during breaks helps reduce CO2 levels, while installing ventilation shutters and grilles during classes ensures better air quality and minimises drafts during colder periods.

In addition, visual CO2 indicators and automated natural ventilation systems, tailored to the school calendar, can optimise air quality and ensure consistent airflow. (7,8)

In cold climates, hybrid ventilation systems, which combine natural and mechanical ventilation, are recommended to save energy while reducing drafts and maintaining comfort. (9)

While natural ventilation offers many benefits, it also presents challenges. Here are three key considerations and their solutions:

The quality of indoor air can be affected by external pollutants, particularly in densely populated urban areas. Addressing this requires careful planning:

Design stage: Openings should be strategically placed to minimise exposure to pollutants.

Post-construction measures: Air filters and indoor plants that purify the air can maintain optimal air quality and promote health.

Balancing natural ventilation with energy efficiency is essential, especially in extreme climates. Strategies include:

Phase change materials (PCM): PCMs absorb or release heat as they change state (e.g., from solid to liquid). They can be integrated into walls, floors, ceilings, or even surface coatings and paints to regulate indoor temperatures.

Thermal inertia: Intelligent use of a building's thermal mass helps reduce temperature peaks, minimise the need for heating and cooling, and ensure consistent air renewal.

Concerns about noise and security can deter the adoption of natural ventilation. Here are practical solutions:

Multi-point locking windows: These enhance resistance to intrusions by securing windows at multiple points.

Security grilles: Installed on windows or ventilation openings, these grilles allow air and light to enter while preventing unauthorised access.

Shutters: Lockable shutters provide added security, particularly when the building is unoccupied. Some designs also allow ventilation through slots or specific openings.

Integrated security systems: Modern ventilation systems may include built-in security features such as alarms or mechanisms to prevent external opening.