Design for the Range, Not the Average: The Prejudice and Inadequacies of Indoor Environment Standards

I recently presented at the Comfort at the Extremes (CATE) conference in Edinburgh. The delegates were a mix of researchers and medics in the fields of indoor air quality and thermal comfort in offices, homes, schools and hospitals. I recognised many from my days as a thermal comfort research back in the 1990s - it was good to catch up after some 25 years. It was also an opportunity for me to have another jibe at the prejudice and inadequacies of current indoor environment standards. This is what I said …

Many years ago, when my kids where younger, and much shorter, I visited Colchester Zoo. I was impressed by the way that each animal enclosure was meticulously designed to ensure each species could thrive as well as survive. I know humans are all one species, but we are very different animals. Then I returned to my homogenous corporate office, a serried sea of open plan desks. That when I thought, surely this environment does not cater for the range of individual human needs and preferences.

Since then, I have been conducting research to understand how we can accommodate the needs of the variety of people that occupy our offices. We reportedly have five generations in the workplace we different needs. I have conducted several surveys exploring the impact of noise on different personality types. I have also helped to design a workplace more suited to neurodiverse occupants - more corporates are employing such people due to their high cognitive performance. Also, more organisations are global attracting staff from a wide variety of cultures and ethnic minorities. From an inclusivity and diversity perspective it is our responsibility to acknowledge and accommodate the needs of such a range of office workers. We must specify and design for the range and not the average, whatever that is. Let’s not forgot that 49.99% of us are below average and 49.99% of us are above average.

My day job is mostly related to the planning and design of offices. But I want to focus here on the indoor environmental conditions. My own database of almost 100 buildings and others, such as the Leesman Index, consistently show that noise, thermal comfort and indoor air quality are the key causes of dissatisfaction with the physical environment in offices. This is not surprising because they are psychophysical variables, and also related to what Herzberg called the hygiene factors. For example, perceived thermal comfort is not the same as temperature (°C), perceived space is not the same as physical size (m²), noise is not simply sound level (dB) and light is not just illuminance (lux). This makes providing for such variables somewhat challenging for building services engineers.

Psychophysics is the study of how people perceive, interpret and react to the world, or more precisely the psychological and physiological response to a physical stimulus. For example, in psychoacoustics, air pressure waves hit the ear drum and through our ear and brains physiology we are able to perceive those waves as sound. However, cognition then kicks in allowing us to interpret that sound and decide whether it is a noise or not. The interpretation depends on multiple personal and situational factors including context, meaning, experience, expectation, activity and personality.

Noise is defined as unwanted sound, which means it depends on the individual and their situation. This is verified by many researchers who only find a weak relationship between sound level and noise annoyance, typically physical sound measurements explain only 25% of the variation in noise annoyance. Logically that means that up to 75% of the variance could be due to psychological and physiological factors. This relationship is further confounded by acousticians arguing over the best physical measure (dB, RT, STI etc.) whereas they should be focussing on their efforts on understanding the 75% non-physical factors.

Over the last few years, Paige Hodsman and I have been researching the effect of noise on different personality types to help mitigate noise issues in open plan offices (Oseland & Hodsman, 2020). We asked office (including home-office) occupants to complete the Big 5 Personality Inventory, a.k.a. OCEAN, and answer questions about the noise in their working environment. Our database currently stands at 2,145 responses. As hypothesised, based on a previous literature review, we found that those more extroverted and less neurotic had fewer concerns with noise and so elements of their performance were less affected by it. Surprisingly, the effect of personality on noise distraction was greater than that of activity. Further multiple regression analyses revealed that 41% of the variance in noise annoyance could be explained by personal factors and psychoacoustic variables.

Consequently, one of our recommendations for reducing noise distraction in open plan offices is to consider the predominant personality type in different teams and design to meet their preferences. So, for example, for a team that might have more introverts such as finance, law or analysts consider a quiet and calming base zone that facilitates focus and concentration. However, additional spaces are also required to facilitate social interaction, meetings and noisier activities. In contrast, if the team is mostly made up of extroverts, such as sales or marketing, then a buzzy and stimulating base zone should be provided but with nearby spaces for quiet and solo activities. However, like most indoor environmental standards, acoustic ones tend to specify a target physical level (such as dB for sound or seconds for RT etc.) based on an assumed average occupant. Admittedly, more recent acoustic standards for open pan offices now consider work activity.

Similarly, lighting standards propose that a 200 lux range around 400 lux is suitable for offices. I have not conducted experiments on lighting, but for my latest book I did review several previously conducted studies of offices (Oseland 2021). These studies indicate that the occupants prefer a range of 900 lux. So, the 200 lux range in standards would not suit most of them. One solution is to have lower ambient lighting, around 200 lux, supplemented by personally controlled task lighting at each desk.

Thermal comfort guidance also tends to recommend a range of preferred temperatures, but at least some (like ISO 7730) recognise that comfort in offices is not only dependent upon temperature but also humidity, air velocity and two personal factors – metabolic rate (Met) and clothing (Clo). The latter two factors are looked up in tables and result in the biggest variation in predicted thermal comfort. The original double heat balance equation, used in ISO 7730 and other standards, is centred around skin temperature and sweat secretion, which are estimated using the looked-up Met. However, the underlying relationship of Met to skin temperature and sweat was derived from experiments on college-age students, rather than a range of people.

Much research on thermal comfort is conducted in a climate chamber. Environmental psychologists, like myself, are not so keen on such an approach because it lacks “ecological validity”. We believe the response of the participants does not reflect those in the real world because i) such studies use college-age students who are often paid, thus affecting their motivation, ii) climate chambers are quite an unrealistic, usually metal-clad, environment, and iii) climate chambers allow specific variables to be controlled but ignore the multiple factors of the real world. Furthermore, the heat balance model is based on steady state exchange physics and treats people as inanimate objects with a simple stimulus-response. Whereas, in reality we are sensing, thinking, experiencing beings that interact, react, change, adapt and evolve to thermal environments.

A further illogical aspect of ISO 7730 is that are there are three classification categories. The higher categories supposedly result in a better quality of thermal environment. However, the higher categories also have tighter bands of recommended temperatures. This approach is based on engineering precision rather than the inclusion of a broader range of thermal comfort requirements. The higher categories and tighter temperature ranges may well cater better for the average person, but not for the range of people found in the modern office.

It is challenging to accommodate a range of thermal comfort requirements in an open plan office, but a single set-point temperature is not the answer. One alternative approach is to use “environmentally responsive workstations” which provide individual control of an under-desk thermal panel and desk height fan. Desk fans are a cheaper alternative in the summer. Another option is to provide a thermal gradient in the office, so that the occupants can choose to sit where they are most thermally comfortable.

It is time to rethink standards, they need a more human-centric starting point rather than be wholly grounded in physics or engineering. They need to be empirical rather than theoretical – the real world is full of unknown variables and humans are the most variable. Models and predictions need to be validated and verified in the real-world with a range of “real” people. A single number derived from highly controlled conditions is highly unlikely to meet the range of human requirements.

In summary:

• We are all one species but different animals
• Design for the range of occupants not the average occupant
• Embrace and design for inclusion and diversity
• A simple single number (such as dB, lux or °C) is not the answer
• Nor is it an excuse for low satisfaction levels
• Provide variety, choice and solutions that work for all