Most companies focus on the energy bill when they talk about building optimisation. That's understandable – but it's only half the equation. The other half is about the people who occupy the building every day. Research demonstrates that an optimised indoor climate can increase productivity by up to 11 percent, significantly reduce sick leave, and lower staff turnover by up to 27 percent.
| 11% Potential productivity increase from optimised indoor environments (World Green Building Council) | 27% Lower staff turnover at WELL-certified office (Cundall, London) | 50% Reduction in sickness absence in the same case (Cundall, London) | Under 1 year Typical payback period - human factors only |
The building as a working environment
An office building is not just four walls and a roof. It is the framework for the hours people spend thinking, collaborating, problem-solving, and creating value. Yet, in many organisations, the building is primarily treated as a cost – something to be run as cheaply as possible.
This is a mistake that can prove costly. European companies typically spend far more on salaries than on rent and building operations. When we focus solely on operational costs and energy consumption, we overlook the far greater potential: that the building can support - or hinder - human performance.
Poor ventilation. Excessively high CO2 levels. Rooms that are too hot or too cold. Lighting that is not adapted to the task or time of day. This is everyday life in thousands of offices, schools, hospitals, and public buildings in Denmark – and it has consequences.
What does the research say?
Productivity: Up to 11 percent
The World Green Building Council has in its report Health, Wellbeing & Productivity in Offices underwent a large number of studies and concludes that an optimised indoor climate, focusing on air quality, temperature, and lighting, can increase employee productivity by 8 to 11 percent – solely through improved air quality.
The figures are supported by an analysis published by Emerald Publishing, prepared by, among others, Professor Per Anker Jensen from the Technical University of Denmark. The analysis shows that buildings with WELL certification consistently report both higher user satisfaction, perceived productivity, and general well-being.
Sick leave: Documented reduction
A study published in PLOS ONE followed organisations that switched to buildings designed based on health and sustainability principles. The result was a 20 percent reduction in sick leave. For a Danish company with 100 employees and an average of 10 sick days per year, this equates to 200 fewer sick days – with a potential saving value of up to DKK 500,000 per year.
Sick Building Syndrome (SBS) occurs in buildings with poor air quality, insufficient ventilation, and unsatisfactory thermal comfort. Symptoms include headaches, fatigue, difficulty concentrating, and irritation of mucous membranes — something that reduces work capacity and increases the likelihood of sick leave.
Fastholdelse: Op til 27 procent lavere personaleomsætning
The engineering firm Cundall redeveloped their London office in 2016 into Europe's first WELL Gold certified office. In the two subsequent years, staff turnover fell by 27 percent and sickness absence by 50 percent — savings that alone covered the investment within the first year.
Recruiting and training new employees typically costs 50 to 200 percent of an annual salary. Therefore, a 27 percent improvement in retention can represent a very significant reduction in personnel-related costs.
The four critical indoor climate parameters
Research and practical experience consistently point to four primary parameters that drive the difference.
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CO2 and air quality
Cognitive abilities begin to decline when CO2 levels exceed 1,000 ppm. Above 1,500 ppm, the effect on decision-making is significant. This is exceeded daily in many Danish offices – without users being aware of it. |
Temperature and thermal comfort
The optimal working temperature is typically 20–22°C. Deviations in either direction lead to loss of productivity — too warm causes fatigue, too cold causes physical discomfort and distraction. |
Human Centric Lighting
Lighting adapted to the time of day and task. Colder tones in the morning support energy. Warmer tones in the afternoon support concentration and prepare the body for rest. |
Daylight and solar shading
Employees in buildings with good daylight penetration report better sleep quality and lower stress levels. Intelligent solar shading balances daylight gain with thermal comfort. |
BACS as a technological foundation
Building Automation and Control Systems — BACS, or in Danish CTS (Central Tilstandskontrol og Styring) — is the technological layer that translates knowledge about the indoor climate into practical improvements. BACS links the technical installations together: ventilation, heating, cooling, lighting, solar shading, and energy monitoring.
Instead of each installation operating in isolation and uncoordinated, an integrated system is created that responds intelligently to the actual use of the building. Key functionalities include real-time monitoring of CO2, temperature and room occupancy; automatic regulation without manual intervention; time control based on activity patterns; and documentation for ESG reports and certifications such as WELL, BREEAM and LEED.
The reconciliation: What is it worth?
The example below is based on documented potentials from research for an office company with 100 employees.
| Average annual salary per employee | £500,000. |
| Total payroll | £50,000,000. |
| Productivity potential (3% improvement — low estimate) | +1,500,000 kr/year |
| Sick leave potential (1 fewer day per employee) | +£250,000/year |
| Retention potential (1 employee retained) | +200–500,000 kr/year |
| Total potential | ~2–2.25 million DKK per year |
A full BACS solution for a building of this size typically costs between 500,000 and 1,500,000 Danish kroner, depending on existing installations and the level of ambition. The payback period based on the human calculation alone – that is, without including energy savings – is therefore typically under a year.
EPBD and the legislative perspective
The EU's Energy Performance of Buildings Directive (EPBD) has since 2024 required the installation of BACS in commercial buildings over a certain size. The directive also covers indoor climate monitoring: From 29 May 2026, indoor climate conditions must be monitored — including temperature and humidity — as part of the BACS requirements.
This means that many building owners are obliged to invest in BACS within the coming years regardless. The strategically wise thing to do is to take it a step further and not just install the minimum required for compliance, but design the solution so that it creates measurable human and economic value.
Frequently asked questions
How much can the indoor climate increase productivity?
Research by the World Green Building Council shows that an optimised indoor climate can increase staff productivity by 8 to 11 per cent — simply through improved air quality. For a company with 50 employees and an average annual salary of 500,000 kr., this equates to a potential added value of up to 2.75 million kroner a year.
Hvad er det kritiske CO2-niveau på kontorer?
At CO2 levels above 1,000 ppm, cognitive abilities begin to decline. At levels above 1,500 ppm, the impact on decision-making and complex thinking is significant. In many Danish offices and meeting rooms, these levels are exceeded daily – without users being aware of it. Modern BACS monitor CO2 in real-time and adjust ventilation automatically.
What is the payback period for a BACS system with a focus on indoor climate?
For a business with 100 employees, the total potential from productivity improvements, reduced absenteeism, and better retention is typically £2 million to £2.25 million per year. A full BACS solution typically costs £500,000 to £1.5 million. The payback period based on human factors alone is therefore typically less than a year – and that's without including the energy savings.
Does the EPBD require indoor climate monitoring?
Yes. From 29 May 2026, the EU's Energy Performance of Buildings Directive (EPBD) will require monitoring of indoor environmental conditions – including temperature and humidity – as part of the Building and Control Systems (BACS) requirements for commercial buildings above a certain size. Many building owners are therefore already obliged to invest in BACS within the next few years.
Hvad er Human Centric Lighting?
Human Centric Lighting (HCL) is a lighting strategy that adjusts the colour temperature and intensity of light to the time of day and the nature of the task. In the morning, cooler, brighter colours support awakening and energy. Later in the afternoon, the light shifts towards warmer tones, supporting calm and focus. Studies show that HCL is associated with increased alertness, better mood, and higher perceived productivity.
Hvad er Sick Building Syndrome?
Sick Building Syndrome (SBS) is a condition that arises in buildings with poor air quality, inadequate ventilation, and unsatisfactory thermal comfort. Symptoms include headaches, fatigue, difficulty concentrating, and irritation of the mucous membranes — something that reduces work capacity and increases the likelihood of sickness absence.
Sources
- World Green Building Council Health, Wellbeing & Productivity in Offices (2014). worldgbc.org
- Per Anker Jensen & Theo van der Voordt: Healthy workplaces: what we know and what else we need to know — Journal of Corporate Real Estate (2020). DOI: 10.1108/JCRE-11-2018-0045
- Juan Palacios, Piet Eichholtz & Nils Kok: Moving to Productivity: The Benefits of Healthy Buildings — PLOS ONE (2020). DOI: 10.1371/journal.pone.0236029
- European Commission Energy Performance of Buildings Directive (EPBD) – Directive 2024/1275, Article 13. eur-lex.europa.eu
- EN ISO 52120: Standardised Building Automation and Control
