There is a test you can run in almost any office building in London right now. You bring in a CO₂ monitor, leave it running for a day, and watch what happens to the numbers by mid-afternoon. In many cases — open-plan offices, meeting rooms with sealed windows, kitchenettes with no mechanical ventilation — the reading will breach 1,000 parts per million (ppm). Often it will reach 1,500. In a badly ventilated conference room during a long meeting, it can hit 2,500 or more.
The question is: what does that mean for the people sitting in those rooms?
−15%
Reduction in cognitive performance when CO₂ levels rise from 550ppm to 1,000ppm — the threshold routinely exceeded in UK offices by mid-morning.
Source: Harvard T.H. Chan School of Public Health, COGfx Study (2015, 2019)
The research on this is not new, and it is not contested. In 2015, the Harvard T.H. Chan School of Public Health published the COGfx Study, which placed office workers in controlled environments with varying CO₂ levels and measured their performance on nine cognitive domains including crisis response, information usage and strategy. The findings were striking: cognitive scores dropped by 15% as CO₂ rose from 550ppm (a well-ventilated space) to 1,000ppm — a level that most offices already exceed before lunch.
A follow-up study in 2019 replicated and extended these results across real-world office environments in six countries. The conclusion was the same. Poor air quality is not just uncomfortable. It is actively degrading the thinking capacity of the people you are paying to think.
Why this matters more than your office layout
The last decade of workplace design has been dominated by one idea: that the open plan is the engine of collaboration and creativity. Walls came down. Hotdesking replaced fixed desks. Glass partitions replaced solid ones. Breakout spaces multiplied. And yet productivity research has consistently struggled to demonstrate that these changes delivered what they promised.
"You can spend £500 per square foot on a workspace redesign. If the ventilation is inadequate, you have spent that money making it easier for people to distract each other while they slowly lose their ability to concentrate."
The reason is that the spatial interventions — the layout, the furniture, the aesthetics — are visible and legible. They feel like change. But the invisible factors — air quality, acoustic performance, thermal comfort, quality of light — are the ones that actually determine how people feel and function in a space. And these are almost always treated as engineering afterthoughts rather than design priorities.
CO₂ is the most measurable of these invisible factors, which is why it makes a useful starting point. Unlike noise, which people notice and complain about, or inadequate natural light, which tends to be masked by artificial lighting, elevated CO₂ is genuinely imperceptible. You do not feel stuffy and think "I must have elevated CO₂." You feel tired, unfocused, slightly irritable — and you attribute it to the meeting, to the commute, to not sleeping well, to having too much on your plate.
550
ppm CO₂ — well-ventilated space. Full cognitive performance.
1,000
ppm CO₂ — typical UK office by mid-morning. 15% cognitive drop.
2,500
ppm CO₂ — common in meeting rooms. Severe impairment of complex thinking.
What good ventilation actually looks like
The WELL Building Standard — the global certification framework for health-focused building design — specifies a maximum of 900ppm CO₂ in occupied spaces, measured over an eight-hour period. That is not an aspirational figure. It is the minimum threshold below which cognitive performance begins to reliably degrade.
Achieving it consistently requires one or more of the following:
Mechanical ventilation with heat recovery (MVHR)
MVHR systems continuously extract stale air and introduce fresh air, recovering heat from the outgoing air to maintain thermal efficiency. In a well-designed office fit-out, this is specified from the outset — ductwork is integrated into the ceiling design, air changes per hour are calculated against occupancy projections, and the system is commissioned to deliver measurable performance rather than theoretical compliance.
Openable windows — but designed, not default
Natural ventilation works, but only when it is designed. A window that opens is not ventilation. A facade strategy that creates cross-ventilation, draws fresh air at low level and exhausts it at high level — that is ventilation. The difference matters because a row of openable windows along one wall of a deep-plan office will ventilate a 6-metre-deep strip and leave the rest of the space stagnant.
CO₂ monitoring and responsive control
In a WELL-certified or WELL-informed design, CO₂ sensors are positioned at breathing height in occupied zones, connected to the building management system, and set to trigger increased air supply when levels rise above threshold. This is not a luxury specification. The sensors cost less than a decent office chair.
"The sensors cost less than a decent office chair. The business case for installing them is stronger than the business case for almost any other investment in the workplace."
The business case — because it matters
If the cognitive performance of your team drops by 15% for four hours of each working day because your office air quality is poor, the financial implications are straightforward to calculate. Take the fully-loaded cost of your team. Multiply by 15%. That is the value of the productivity you are losing — every day, invisibly, because of a design decision that was never made or was made without this information.
The WELL Building Standard requires that commercial spaces document their ventilation performance and air quality. Organisations that have pursued certification — or have simply applied WELL principles without formal certification — consistently report reduced absenteeism, lower staff turnover and higher employee-reported wellbeing scores. These are not soft metrics. They translate directly into recruitment costs, sick pay, and output.
For employers navigating return-to-office dynamics, this matters in another way too. People now have a year-round basis for comparison between their home environment and their office. If the office makes them feel worse — more tired, less sharp, harder to concentrate — that is a data point they carry into every conversation about hybrid working. Good air quality will not resolve every tension in that conversation. But its absence will reliably make it worse.
What this means for your space
If you manage or occupy a commercial space, the first step is simply to measure. A CO₂ monitor costs between £50 and £200. Leave it running in your main workspace and your meeting rooms for a week. Look at the data. If readings consistently exceed 900ppm during occupied hours, you have an air quality problem — and the architectural solutions are well understood and, relative to the cost of the problem, not expensive.
If you are planning a fit-out, a refurbishment or a new workspace, air quality should be specified with the same rigour as fire safety or accessibility. Not because it is required by regulation — current UK building regulations are considerably more permissive than the WELL thresholds — but because the evidence for its impact on performance is stronger than the evidence for most of the other decisions you will make about the space.
The buildings we work in are not neutral containers. They are active participants in how we think, how we feel, and how well we do the work we are there to do. Most of the time, we do not notice. That invisibility is precisely the problem.
Indomo is a RIBA Chartered architecture and interior design practice specialising in wellness-informed design. As a WELL Accredited Professional, Mara Bravo works with residential and commercial clients across London and Spain to design spaces that measurably improve the health and performance of the people inside them. If you would like to understand how your current space is performing, we start with a conversation — no obligation.