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Cities & Health
ISSN: (Print) (Online) Journal homepage: https://www.tandfonline.com/loi/rcah20
Prioritising indoor air quality in building design
can mitigate future airborne viral outbreaks
Otis Sloan Brittain , Hannah Wood & Prashant Kumar
To cite this article: Otis Sloan Brittain , Hannah Wood & Prashant Kumar (2020): Prioritising
indoor air quality in building design can mitigate future airborne viral outbreaks, Cities & Health,
DOI: 10.1080/23748834.2020.1786652
To link to this article: https://doi.org/10.1080/23748834.2020.1786652
Published online: 28 Jul 2020.
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COMMENTARY AND DEBATE
Prioritising indoor air quality in building design can mitigate future airborne
viral outbreaks
Otis Sloan Brittain
a
, Hannah Wood
a
and Prashant Kumar
b
a
Architect MAA, ARB, Ingvartsen Architects, BOVA Network, Copenhagen, Denmark;
b
Global Centre for Clean Air Research (GCARE),
Department of Civil and Environmental Engineering, Faculty of Engineering and Physical Sciences, University of Surrey, Guildford, UK
ABSTRACT
The ongoing COVID-19 pandemic has brought into focus how poor indoor air quality can amplify
the eects of airborne viruses. Rather than promoting health and wellbeing, our built environment
often worsens air quality through inadequate ventilation, air recirculation, material specication and
the additional pollution load from mechanical heating and cooling. In this think-piece, we introduce
a selection of interrelated building design strategies to improve indoor air quality and reduce the
spread and impact of airborne disease. We also highlight the need for interdisciplinary collaboration,
targeted policy change and leadership on air quality to build resilience against future airborne viral
outbreaks.
ARTICLE HISTORY
Received 5 May 2020
Accepted 18 June 2020
KEYWORDS
COVID-19; healthy buildings;
SARS-CoV-2 virus
While much of the world is self-isolating at home, the
COVID-19 pandemic has brought into focus the
adverse effects that the built environment can have
on our health, especially due to poor indoor air qual-
ity. It is currently understood that the COVID-19
virus is spread via exhaled respiratory droplets (the
propagation of which is shown in Figure 1) that appear
to have a higher stability in indoor air when compared
to outdoor air (Kumar and Morawska 2019); and high
levels of common indoor pollutants strongly promote
COVID-19 transmission (Li et al. 2020a). Poor indoor
air quality, stemming from both indoor sources and
the ingress of outdoor pollutants, is worsened by
inadequate ventilation, lack of air filtration and air
recirculation within enclosed spaces. These factors
can, therefore, be the difference between containing
the spread of a novel coronavirus and the infection of
an entire building. Instead of integrating healthy
indoor air quality strategies into the design of
a building, complex Heating, Ventilation and Air
Conditioning (HVAC) systems are commonly added
in the latter stages of the design process to control the
characteristics of indoor air, and generally prioritise
thermal comfort above the occupant’s health.
The significant drop in the level of some outdoor
air pollutants seen during the COVID-19 economic
shutdown highlights how polluted the ambient air in
our cities has become. High ambient air pollution is
tightly associated with increased COVID-19 transmis-
sion (Li et al. 2020a), decreased lung function and
greater risk of developing chronic respiratory diseases,
such as Chronic Obstructive Pulmonary Disease
(COPD) and asthma (Cui et al. 2003, Li et al. 2020a).
It is also becoming evident that the impact of COVID-
19 is much greater for those with existing health con-
ditions or a weakened immune system. The combina-
tion of high ambient air pollution levels and a novel
coronavirus, therefore, puts a population at greater
risk. This is supported by past studies which have
drawn a correlation between high ambient air pollu-
tion levels and increased mortality rates from diseases
caused by other coronaviruses, such as Severe Acute
Respiratory Syndrome (SARS) (Cui et al. 2003).
Concerningly, it has often been found that pollutant
concentrations are higher in indoor air than outdoor
air, owing to activities such as cooking indoors (Chen
and Zhao 2011). Therefore, strategies to improve the
quality of indoor air must be prioritised alongside
those to improve ambient air quality at an urban
scale to reduce a population’s risk factors when con-
fronted with a novel airborne virus, such as SARS-
CoV-2.
Adequate ventilation, air filtration, humidity regu-
lation and temperature control are key strategies
which can be combined to improve indoor air quality
and protect occupants from airborne diseases.
Appropriately ventilating spaces with clean outdoor
air and minimising recirculation within a building are
fundamental ways to reduce the build-up of indoor air
pollutants and humidity and decrease the spread of
airborne viruses (Kumar and Morawska 2019). Recent
studies suggest that the SARS-CoV-2 virus spreads
more effectively in poorly ventilated indoor environ-
ments (Li et al. 2020b) and that it may be present on
the surface of airborne particulate matter (Setti et al.
2020). Research also suggests that for similar viruses
CONTACT Hannah Wood hw@ingvartsen.dk Architect MAA, ARB, Ingvartsen Architects, Nikolaj Plads 23, 2, Copenhagen K 1067, Denmark.
CITIES & HEALTH
https://doi.org/10.1080/23748834.2020.1786652
© 2020 Informa UK Limited, trading as Taylor & Francis Group
such as influenza, an air volume exchange rate of 3
changes per hour, with clean outdoor air, may have
the same mitigating effect as vaccinating 50–60% of
the population (Smieszek et al. 2019). In recent years,
there has been an uptake of Demand Controlled
Ventilation (DCV) systems across building typologies,
which minimise the ingress of outdoor air so that less
energy is required to maintain a comfortable indoor
temperature. As the use of DCV systems encourages
the recirculation of air within enclosed spaces, a nexus
emerges between energy consumption and its conse-
quent impact on indoor air quality.
The use of passive design strategies to encourage
natural ventilation and air distribution – such as
building orientation for optimum airflow, appropri-
ately designed openings, effective spatial sequencing
and passive stack ventilation – should be prioritised as
they require minimal energy input and maintenance
over the lifespan of a building. If such measures were
to guide architectural decision-making and were tai-
lored to local climatic and site conditions, reliance
upon add-on mechanical solutions, such as HVAC
systems, could be minimised. In recent years,
Computer Aided Design (CAD) tools to simulate nat-
ural ventilation and air distribution, both inside
a building and its surroundings, have continuously
been improving. Developments in Building
Information Modelling (BIM), parametric modelling
and Computational Fluid Dynamics (CFD), in combi-
nation with improved access to fast and inexpensive
cloud-based processing, have made airflow simulation
tools increasingly accessible to built environment pro-
fessionals. As these tools have the potential to generate
predictive models that can simulate how airborne
pollutants and viral particles profligate and spread in
a given context, they may also help to bridge the
knowledge gap which persists around airborne viral
transmission in the built environment. Such models
would have far-reaching applications across a range of
fields, including building design, where they could be
used to inform strategies to optimise natural ventila-
tion and air distribution and mitigate the spread of
airborne viruses. However, for models to be calibrated
to a useful level of accuracy, they will require addi-
tional quantitative experimental data – often con-
strained by practical challenges such as obtaining
affordable and accurate instrumentation which does
not add significant heat – and close collaborations
between microbiologists, indoor air quality scientists
and building flow dynamics specialists.
At sites with high ambient pollution levels, where
natural ventilation presents significant challenges,
incoming outdoor air can be filtered using appropriately
sized High-Efficiency Particulate Air (HEPA) filters to
remove viral particles and pollutants, such as PM
2.5
and
NO
2
, which are understood to strongly promote
COVID-19 transmission (Li et al. 2020a). For most
building typologies, designers should avoid relying solely
upon mechanical filtration as it requires constant energy
input and maintenance demands are often neglected.
A number of natural indoor air filtration systems, such
as plant- or algae-assisted biofilters, are currently under
Figure 1. Propagation of exhaled airflow from a pair of subjects face to face talking and breathing. (Image reference: (Xu et al.
2016).
2O. SLOAN BRITTAIN ET AL.
development, however, more research is needed in terms
of their efficacy in removing air pollutants and their
effects on relative humidity. While the use of plants to
improve indoor air quality has been popularised in
recent years, as an isolated measure it is impractical at
a building scale, as it requires at least one plant per m
2
to
have a substantial impact on indoor air quality
(Cummings and Waring 2020).
The specification of non-toxic, breathable and moist-
ure-regulating materials and surface coatings are a low-
energy strategy to improve indoor air quality and long-
term respiratory health, therefore increasing occupant
resilience when confronted with a novel airborne virus.
For example, building materials such as lime and
unfired clay passively regulate relative humidity by
absorbing and releasing water vapour into the air, there-
fore reducing the need for mechanical dehumidifica-
tion. To achieve a healthy indoor humidity level,
however, requires a delicate balance. Low relative
humidity is thought to favour the survival and trans-
mission of viruses spread via respiratory droplets as it
enhances evaporation from exhaled bioaerosols, result-
ing in smaller droplet nuclei which remain airborne for
an extended period (Wolkoff 2018). While, conversely,
high relative humidity encourages the growth of indoor
mould and mildews, which are linked to an increased
risk of asthma and allergies (Mendell et al. 2011). In
addition, the chemical properties of materials can play
a key role in slowing the spread of pathogens and
prevent cross-contamination between indoor surfaces.
As the SARS-CoV-2 virus has been shown to survive
longer on certain materials – up to 3 days on plastic and
stainless steel (van Doremalen et al. 2020) – antimicro-
bial materials such as copper-alloys, which destroy or
prohibit the multiplication of pathogens, should be
considered for high contact surfaces, like countertops
and door handles. Specifying antimicrobial materials
can also reduce the need for cleaning products,
a common source of indoor Volatile Organic
Compound (VOC) pollution.
Indoor temperature control, both heating and cool-
ing, remains reliant on the burning of fossil fuels
which contributes to high ambient urban pollution
levels and therefore the sustained transmission of
COVID-19 (Li et al. 2020a). During the recent coro-
navirus lockdown in China, it emerged that in cooler
cities such as Beijing the drop in ambient air pollution
was notably lower compared to warmer Chinese cities,
due in part to a reliance on coal-powered heating for
homes and the lower natural dispersion of airborne
pollution associated with cooler climates. Similarly,
there is a significant global energy demand for indoor
cooling – the air conditioning unit is now an expected
fixture in buildings around the world. However,
mechanical air temperature regulation in most cli-
mates can be minimised, or eliminated entirely, by
integrating passive temperature control strategies
into the architectural design process. Strategies that
prioritise the introduction of clean outdoor air can
also help to prevent the build-up of indoor humidity,
pollutants and viral particles. Generally, in hot cli-
mates, indoor airflow should be optimised and com-
bined with an appropriate use of thermal mass; while
in cooler climates incoming outdoor air can be pre-
heated through passive systems such as solar heaters
and transpired solar collectors, or in mechanical ven-
tilation heat recovery (MVHR) systems.
As the enforced lockdowns begin to lift over the
coming months, it is unlikely we will suddenly become
an outdoor species. Before the COVID-19 pandemic
took hold, urban dwellers in industrialized nations
spent over 90% of their time indoors, and, according
to the WHO, exposure to indoor pollutants contribu-
ted to around 4.3 million premature deaths each year.
Given the amount of time people spend indoors, and
the future likelihood of airborne viral outbreaks, it is
important to re-evaluate how both new buildings and
our existing building stock can be designed in order to
improve indoor air quality. Built environment profes-
sionals should take the lead in the selection and imple-
mentation of bespoke design strategies tailored to local
climatic conditions which require minimal energy
inputs and maintenance over the lifespan of
a building. Research opportunities have been brought
to light in the fields of viral airborne transmission and
detection within the built environment; the effect of
building materials on indoor air quality; and the appli-
cation of breathable, non-toxic and moisture-
regulating materials at scale. While the COVID-19
pandemic has highlighted the need to prioritise design
strategies which improve indoor air quality, for these
approaches to be successful – and to overcome the
inertia of powerful industry stakeholders – it is critical
that they are supported by targeted policy change
across the public health, urban planning and building
design sectors. As, according to the WHO, over 90% of
the world’s population currently live in places that
exceed ambient air quality guidelines, to improve
indoor air quality will also require decisive leadership
at municipal, national and international levels to
enhance the quality of the ambient air in our cities.
Disclosure statement
No potential conflict of interest was reported by the authors.
Notes on contributors
Otis Sloan Brittain and Hannah Wood are both architects
with a shared research interest in health and the built envir-
onment. They are currently managing the design and con-
struction of 110 prototype homes in Tanzania for Ingvartsen
Architects, part of a 3-year randomised controlled trial that
investigates how housing design impacts family health. Otis
CITIES & HEALTH 3
also has an interest in how algae can improve indoor air
quality and how this research can be applied in the design of
building components. Hannah and Otis have previously
contributed to research papers for Cities & Health (2019)
and Plos-MED (2018).
Prashant Kumar is a Professor & Chair in Air Quality and
Health, founding Director of Global Centre for Clean Air
Research (GCARE), at the University of Surrey, UK; and an
Adjunct Professor at Trinity College Dublin, Ireland. He
researches urban air pollution, its sources, dispersion and
exposure assessment; have published >200 journal articles
attracting >6650 citations and h-index of 45. He has secured
>£6.5 M research funding from RCUK & international bodies,
serves editorial board of several journals and reviews/advises as
a panel member many funding agencies worldwide.
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