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Why indoor air quality is important and how to improve it

By VELUX Commercial
University of Southern Denmark featuring VELUX Modular Skylights
University of Southern Denmark featuring VELUX Modular Skylights

Did you know that well-designed classrooms have a significant influence on academic performance? Studies have found that improved physical characteristics of classrooms can boost the learning outcomes of students.

In this article, we take a look at the importance of air quality and present some of the best ways that architects and designers can improve air quality in classrooms.

"The physical characteristics of primary schools have a substantial impact on the learning progress of students."

This was the overriding conclusion of researchers from the University of Salford, Manchester, in the Clever Classrooms Study, 2015¹. The study looked at the performance of 3,766 students and found that factors such as light, temperature and air quality account for 16% of the variations in academic progress made over the space of a year.

Let’s start by looking at some of the ways that air quality affects both health and performance in students.

ebook: Designing great schools: 8 examples of how skylights improves learning

The importance of indoor air quality

Since students spend most of their time indoors, it is crucial to understand how air quality affects them. Indoor air quality is generally a product of two factors: pollutants generated indoors; and the levels of pollution in outdoor air surrounding the building. Indoor air with high levels of pollutants can cause general discomfort and a range of negative health effects, including irritation of the eyes, nose and throat.

Good indoor air quality creates a sense of comfort and well-being. The pleasant sensation of pollution-free air, as well as its positive effects, can be felt immediately when a person enters a room. It can improve general well-being and even mental performance.

A recent study² conducted to improve ventilation in 16 classrooms demonstrated how high-quality indoor air improves the learning progress of students. Computerised tasks performed by more than 200 students showed "significantly faster and more accurate responses for choice reaction, colour word vigilance, picture memory and word recognition, at higher ventilation rates"².

CO2 as a key indicator

We now know that indoor air quality affects both health and performance. But which indicator for indoor air quality is generally used in schools and other learning environments?

CO2 – carbon dioxide – is the most relevant indicator for indoor air quality as it relates to people, whether in homes, offices or schools. CO2 is measured in parts per million (ppm).

Levels indoors rise as a result of human activity and can only be lowered through ventilation. The more CO2 that is present in a room, the more pollutants you are likely to experience overall.

What constitutes good air quality?

Outdoor CO2 levels are approximately 400 ppm. As breathing generates CO2, indoor air will always have a higher concentration when people are present.

A CO2 level of up to around 1,150 ppm is considered good air quality. 1,400 ppm will be acceptable in most situations, although not for prolonged periods. CO2 levels above 1,600 ppm indicate lower air quality, and exposure time above this level should be minimised.

With our key indicator in place, it’s time to look at how designers and architects can improve air quality in buildings.

How to improve air quality

There are three commonly used ways to ensure good indoor air quality:

  1. Minimise indoor emissions
  2. Keep rooms dry
  3. Ventilate well

On top of these, there are other methods that designers and architects can consider when designing classrooms.
Researchers from The University of Salford, describe some of them in their Clever Classrooms study (2015)¹:

  • Big window opening sizes, at different levels and orientations increase the air exchange rate and provide ventilation options for different conditions. Window controls should be easy to access and use.
  • Increasing the ceiling height can improve air quality in the short term by absorbing more stale air, but proper ventilation is still needed.
  • User-controlled ventilation allows users to ventilate the room effectively, ideally with access to windows with large opening sizes.
  • A CO2-meter in classrooms allows teachers and pupils to easily see when they need to correct their environment.
  • Natural ventilation through windows and skylights provides large volumes of fresh air on demand. Mechanical ventilation can also improve air quality when there is limited space for windows.


  1. Clever Classrooms (2015), Summary report of the HEAD project, University of Salford, Manchester
  2. Bakó-Biró, Z., D. J. Clements-Croome, N. Kochhar, et al. (2012), "Ventilation rates in schools and pupils’ performance." Building and Environment 48 (0): 215-223.

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