The research behind human performance in the built environment.
Buildings affect how people think, how they feel and how often they get sick. Published research shows by how much.
Evidence Design
We use the GRADE framework to score evidence quality. GRADE is the international standard used by WHO and Cochrane. HIGH means strong study design, adequate sample and consistent results.
What follows is a selection. The evidence we produce for clients is specific to the project, the building type and the users.
Market
$548B
Wellness Real Estate market 2024
Projected to double by 2029.
GWI 2025
Market
$6.2T
Cumulative GDP gains from brain health interventions
Modeled across 12 intervention categories including built environment, sleep and light exposure.
WEF / McKinsey 2026
Finance
4.6–4.8%
Higher rents for Fitwel-certified offices
Controlled for location, age, size and LEED status. The premium is attributable to health certification alone.
Cambridge 2025
Finance
10–25%
Price premium for wellness residentials
Buyers pay more for homes with biophilic design, air quality systems and circadian lighting.
GWI 2025
Finance
235%
Stock appreciation of wellness-focused companies
Compared to 159% for the S&P 500 over the same period.
GRESB
Investors
85–91%
Institutional investors prioritize healthy buildings
Pension funds, sovereign wealth funds and REITs now rank occupant health alongside energy efficiency.
EY 2024
Finance
$411B
Annual US cost of poor sleep
Indoor environments drive sleep quality through light exposure, noise and thermal conditions.
IWBI 2025, compiled from CDC/BLS data
Finance
$150B
Annual US cost of presenteeism
Employees present but underperforming due to poor indoor conditions cost more than absenteeism.
IWBI 2025, compiled from CDC/BLS data
Market
28%
Satisfaction increase in WELL-certified buildings
Also: 26% wellbeing increase and 10-point productivity gain.
IWBI 2025
Market
23%
Office workers report Sick Building Syndrome
SBS causes 35% higher absenteeism. Poor ventilation is the primary driver.
IWBI 2025
Regulation
May 2026
EPBD IEQ transposition deadline
EU member states must transpose indoor environmental quality requirements into national law.
EU Regulation
Regulation
2030
CSRD social metrics mandatory
Large companies must report on social sustainability, including occupant wellbeing in owned and leased buildings.
EU CSRD
Research · HIGH
+61%
Cognitive function in green vs. conventional offices
Office professionals scored 61% higher on cognitive tests in buildings with optimized air quality. Controlled exposure study.
Allen et al., 2016. Environmental Health Perspectives
Research · HIGH
+25%
Cognitive gain from doubled outdoor air supply
Doubling outdoor air from 20 to 40 cfm per person improved scores in 8 of 9 cognitive domains.
Allen et al., 2016. Environmental Health Perspectives
Research · HIGH
−21%
Cognitive decline per 400 ppm CO₂ increase
Each 400 ppm increase reduced cognitive scores by 21% across all domains. Controlled office study.
Allen et al., 2016. Environmental Health Perspectives
Research · HIGH
−69%
Information processing at 2,500 ppm CO₂
Healthy adults, 2.5 hours exposure. 44–94% decline across cognitive dimensions.
Satish et al., cited in Palacios Temprano, 2020. BMJ Open
Research · HIGH
+18%
Cognitive gain from doubled ventilation rate
20 cfm/person increase in outdoor air supply. Same controlled office, different intervention pathway.
Allen et al., 2016. Environmental Health Perspectives
Research · HIGH
−5%
Learning outcomes from elevated CO₂ in classrooms
Primary and secondary school students. Dose-response relationship confirmed.
Hartke, 2025
Research · HIGH
−2.5%
Daily attendance drop from poor indoor air in schools
Reducing CO₂ concentration improves both learning and attendance.
Hartke, 2025
Research · HIGH
2,700 ppm
CO₂ threshold for EEG-measured drowsiness
Fatigue increased significantly in a naturally ventilated office. Prior sleep deprivation amplified the effect.
Zhang et al., 2019. Building and Environment
Research · HIGH
4x
CO₂ difference between closed and ventilated bedroom
2,873 vs. 681 ppm. Sleep quality dropped measurably. Children aged 10–12. Double-blinded crossover.
Lassen et al., 2023. Int J Occup Med Environ Health
Industry
$200B
Annual US losses from Sick Building Syndrome
Reducing SBS symptoms by 20–50% through better IAQ would yield up to $200 billion annually.
IWBI 2025
Industry
25%
Europeans below indoor air quality standards
One in four Europeans live in buildings where IAQ falls below national standards.
BPIE, Healthy Buildings Barometer 2024
Industry
121M
Workdays lost to respiratory illness per year
US economic data. Indoor air quality is a direct contributor.
IWBI 2025, compiled from CDC/BLS data
Research · HIGH
+79%
Cognitive control from optimized daylight
Knowledge workers scored 79% higher after a full work week. The effect accumulated day by day. Controlled crossover study.
Boubekri et al., 2020. IJERPH
Research · HIGH
+42%
Decision-making with daylight access
Optimized daylight vs. blinds-closed condition. p < 0.0001.
Boubekri et al., 2020. IJERPH
Research · HIGH
+37 min
More sleep per night with daylight-optimized office
Actigraphy-measured, knowledge workers, weekday effect.
Boubekri et al., 2020. IJERPH
Research · HIGH
+42%
Productivity from larger window-to-wall ratio
26–62% higher cognitive scores across 9 domains of strategic thinking.
Boubekri et al., 2020. IJERPH
Research · HIGH
8x
Higher satisfaction from daylight access
Odds ratio 8.0. Workers with electrochromic glazing vs. standard windows reported dramatically higher satisfaction.
Boubekri et al., 2021. Frontiers in Sustainable Cities
Research · HIGH
+77%
Mood improvement from daylight access
Electrochromic glazing vs. standard windows with fixed roller shade. Crossover study.
Boubekri et al., 2021. Frontiers in Sustainable Cities
Research · HIGH
250 lux
Minimum daytime light for circadian health
International consensus of 15 researchers. Evening exposure should stay below 10 lux. Most indoor environments fail this threshold.
Brown et al., 2022. PLOS Biology
Research · HIGH
−3 days
NICU length of stay from cycled light
Preterm infants. Cycled light vs. dimmed or near-darkness. Cochrane systematic review.
Cochrane Database of Systematic Reviews, 2024
Research
−7.3h
Hospital stay reduction per 100 lux daylight
In rooms varying by 500 lux, the average reduction was 36.5 hours. 1.5 fewer days per patient.
Terrapin Bright Green, 2023
Research
−17.4h
Hospital stay reduction with outside views
Independent of daylight levels. Views and daylight have additive effects.
Terrapin Bright Green, 2023
Research
−16%
Sick leave reduction with landscape views
11 fewer hours per year per employee. Controlled for job type, age and location.
Terrapin Bright Green, 2023
Research
+5.2%
GDP from improved classroom daylight
A 0.25 SD improvement in test scores estimated to yield 5.2% GDP increase over a generation.
Terrapin Bright Green, 2023
Research · MODERATE
−39%
Working memory loss from speech noise in children
Second-graders: 39% drop. Adults: 11%. Children are 3.5 times more vulnerable to irrelevant speech.
Klatte et al., 2013. Frontiers in Psychology
Research · HIGH
70 dB
Traffic noise level that impairs cognition
Significantly more errors. Physiological stress markers confirm the effect is not subjective (d = 2.66).
Schlittmeier et al., 2015. Noise and Health
Research · HIGH
>50 dB
Office noise threshold for physiological fatigue
Wearable sensors on government office workers. Objective physiological markers.
Srinivasan et al., 2023. npj Digital Medicine
Research · MODERATE
−11%
Working memory loss from speech noise in adults
Same study. Even trained adult cognition is affected by irrelevant speech in open-plan environments.
Klatte et al., 2013. Frontiers in Psychology
Research · HIGH
<40 dB
Night noise threshold for immune recovery
ICU patients with noise below 40 dB showed better melatonin levels and immune markers after major surgery.
2017. Molecules
Research · HIGH
Ceiling
Sound-absorbing tiles reduce hospital stress
Coronary care unit. Replacing reflective with absorptive tiles improved sleep, reduced stress and lowered re-admission rates.
2008. Journal of the Acoustical Society of America
Research · HIGH
0%
Noise-cancelling headphones do not improve cognition
Open-plan office. ANC improved perceived acoustic environment but had zero effect on working memory.
2022/2024. INTER-NOISE
Research · HIGH
70 dBA
Railroad noise impairs math and working memory
Office workers with open windows. Both digit span and mathematical performance declined. Dose-response confirmed.
2023. Journal of the Acoustical Society of America
Research · HIGH
d = −1.58
White noise reduces pain in preterm infants
Large effect. 50–55 dB in neonatal intensive care. Meta-analysis of randomized controlled trials.
2024. Nursing Open
Research · HIGH
EDA ↑
Noise triggers measurable bodily stress
Electrodermal activity increased at 70 dBA from transportation noise. Not annoyance — real physiological stress.
2023. Journal of the Acoustical Society of America
Research · HIGH
NICU
White noise improves preterm infant sleep
50–55 dB, 20-minute sessions before feeding. Meta-analysis of randomized controlled trials.
2024. Nursing Open
Research · HIGH
Privacy
Acoustic privacy matters more than noise level
Open-plan offices: perceived privacy improved with sound masking, but cognitive performance did not change.
2022. Office acoustics study
Research
59.6%
Stress reduction in biophilic recharge rooms
Healthcare worker stress. Rooms with natural elements, nature imagery and soundscapes. Now permanently installed at 60+ US hospitals.
Terrapin Bright Green, 2023
Research · HIGH
d = 0.86
Nature increases positive emotions (meta-analysis)
Large effect across 85 studies. Natural vs. urban environments. Multiple countries and methods. Both immersive and simulated settings.
Browning et al., 2022. Frontiers in Psychology
Research · HIGH
d = −0.67
Nature reduces negative affect (meta-analysis)
Medium to large effect. Same 85-study meta-analysis. Natural environments reduce sadness, anxiety and fatigue relative to urban settings.
Browning et al., 2022. Frontiers in Psychology
Industry
$36,471
Additional productivity per employee per year
Biophilic design in commercial offices. Certified healthy buildings command 4-6% rental premiums.
IWBI 2025
Research · HIGH
4 min
Biophilic elements reduce blood pressure within minutes
VR office study. Blood pressure dropped measurably within 4 minutes of biophilic exposure. 100 participants.
Yin et al., 2019. Environment International
Research · MODERATE
+15%
Productivity from indoor plants
Longitudinal study. Adding plants to a minimalist office increased measured work output by 15%.
Nieuwenhuis et al., cited in Hartke, 2025
Research
−10%
Absenteeism reduction in biophilic offices
Employees with nature views took fewer sick days. Students in classrooms with vegetation had fewer absences.
Terrapin Bright Green, 2023
Research
−24%
Faster wound healing in stress-reduced environments
Patients with indoor vegetation recovered faster from surgery and required less pain medication.
Terrapin Bright Green, 2023
Research · MODERATE
1.74
Stress recovery score in biophilic environments
Highest biophilic design level scored 1.74. Non-biophilic environments scored −0.37. Attention, safety and inspiration were also negative without biophilia.
Xing et al., 2025. PLOS ONE
Research · HIGH
HRV ↑
Green views activate parasympathetic nervous system
Viewing green space from a high-rise window significantly increased heart rate variability compared to urban views. Physiological relaxation, not just preference.
2020. Urban Forestry & Urban Greening
Research · HIGH
Mood ↑
Green window views improve psychological state
Profile of Mood States and semantic differential both showed significant improvement when viewing green space vs. urban landscape. High-rise office setting.
2020. Urban Forestry & Urban Greening
Research · HIGH
Cognition ↑
Working memory and concentration higher with nature views
Windows with views outperformed windowless conditions on working memory and concentration. No effect on creativity or short-term memory. Controlled laboratory study.
2020. Building and Environment
Research · HIGH
−10%
Cognitive decline per degree above 24°C
Even when thermal comfort was maintained by adjusting clothing and air velocity. 4.5 hours exposure. 36 subjects.
2021. Indoor Air
Research · HIGH
22°C
Peak performance temperature
Text processing, calculations, call-center handling. Performance peaks at 22°C and declines above and below. Largest workplace meta-analysis.
Seppänen et al., 2006
Research · HIGH
9.9%
Learning improvement at optimal temperature
EEG-measured. College students across five thermal conditions. Performance peaked at neutral comfort (PMV 0).
2020. Building and Environment
Research · MODERATE
−15%
Test scores on days above 32°C
4.6 million high school exit tests, New York. Each additional hot day during the school year reduces learning outcomes.
Park, cited in Palacios Temprano, 2020. BMJ Open
Research
−25%
Sick leave reduction from optimized indoor climate
Buildings with better air quality, daylight and thermal comfort reduce absenteeism by up to a quarter.
WHO / Milton et al., 2000
Industry
15-20%
Efficiency gain from thermal comfort
Improving indoor thermal comfort improves employee work efficiency. Thermal discomfort reduces cognitive performance and increases errors.
IWBI 2025
Research · HIGH
50% RH
Lower humidity improves cognition at high temperatures
When relative humidity decreased from 70% to 50% at 39°C, cognitive test accuracy increased significantly. Climate chamber study.
2020. Indoor Air
Research · HIGH
Air quality ↓
Perceived air quality worsens with rising temperature
The acceptability of air quality decreased linearly with increasing temperature at 70% relative humidity. Thermal and air quality are coupled.
2018. Indoor Air
Research
r = 0.64
Higher humidity linked to insomnia severity
Continuous sensor-based humidity measurement in homes of older adults. Direct correlation with sleep quality.
2025. Innovation in Aging
Research
Multi-sensory
Thermal, acoustic and light conditions interact
Acoustic comfort is highest at 25°C. Noise perception is worst when also thermally uncomfortable. Environmental factors are not independent.
2018. Building and Environment
Research
<40% RH
Low humidity increases virus survival on surfaces
Relative humidity below 40% associated with higher survival of influenza and coronavirus on indoor surfaces. Standard offices in winter often fall below this threshold.
2020. Building and Environment
Research
Respiratory ↑
Cold, dry air promotes respiratory infection
Low humidity dries mucosal surfaces and reduces ciliary action that removes airway contaminants. Indoor environments in winter are a primary driver.
2013. Indoor Air
Research · HIGH
fMRI
Room geometry activates brain reward circuits
Rooms with curved contours rated more beautiful and approached more. High ceilings activate pleasure circuits. Low enclosure promotes approach behavior. The brain evaluates architecture through reward systems.
Vartanian et al., 2015. Proceedings of the National Academy of Sciences
Research
Abstract ↑
High ceilings change how people think
10-foot ceilings activated relational, abstract processing. 8-foot ceilings activated item-specific thinking. The effect is unconscious, mediated by perception of freedom vs. confinement.
Meyers-Levy & Zhu, 2007. Journal of Consumer Research
Research
EEG
Low ceilings increase physiological stress
Rooms with lower ceiling heights showed reduced alpha-to-beta wave ratio, indicating higher stress and arousal. The interaction with window ratio and room proportions is complex.
2024. Building sciences
Research
−72%
Open offices reduce face-to-face interaction
After transitioning to open plan, face-to-face interactions dropped 72%. Email and messaging increased 56%. The opposite of what was intended.
Bernstein & Turban, 2018. Phil. Trans. R. Soc. B
Research
6x
Seating geometry determines conversation frequency
Corner seating produced 6 times more conversations than face-to-face across a table and twice as many as side-by-side. 50 observation sessions in a hospital cafeteria.
Hall, 1966. The Hidden Dimension
Research
300%
Pedestrian space tripled, social activity tripled
Copenhagen 1968-1986. As pedestrian streets and squares tripled, the number of people standing and sitting in the city center tripled. Direct link between spatial allocation and human behavior.
Gehl, 1987. Life Between Buildings
Research · HIGH
Inconsistent
Prospect-refuge theory not validated for interiors
Meta-analysis: evidence for prospect-refuge preferences is inconsistent when applied to architectural contexts. Results from natural environments should not be directly transferred to buildings.
2016. City Territory and Architecture
Research
Sigmoid
Spatial perception follows nonlinear rules
Room height perception follows a sigmoid function. Height reductions are undershot by 33%. Increases are overshot by 12%. The spaces you were in before shape how you experience the next one.
2026. Spatial Perception in Architectural Transitions
Research
Color
Color reduces anxiety and aids orientation
Optimized color reduces anxiety in educational environments. Color aids wayfinding in hospitals. Chromatic designs increase pleasure over achromatic settings.
Compiled from multiple studies, 2023-2025
Research
Anxiety ↑
Low ceilings without windows trigger patient distress
Patients reported significant distress receiving diagnoses in small rooms with low ceilings and no windows. High ceilings and views recommended to prevent anxiety.
2023. Systematic review, HERD
Research
Diffuse
Unclear spatial boundaries inhibit social interaction
Suburban areas and large spaces without clear spatial definition produce less community interaction. Clear edges, proportioned enclosure and legible paths promote use.
Gehl, 1987. Life Between Buildings
Research
Mixed-use
Single-function zones degrade over time
Large-scale housing estates with monofunctional zoning consistently showed material and social degradation. Mixed use sustains activity, safety and community life.
Compiled from urban planning studies