Trends through time

Since the earliest human shelters and primitive buildings, the key objectives in building design have been to provide comfort and protection from the weather while allowing for a supply of fresh air.

Designers achieved this in various ways, but the challenge has always been providing fresh air without sacrificing that comfort and protection. Before air conditioning, passive systems were prevalent in vernacular architecture, from the hypocaust of Ancient Rome to the bagdir of Iran, relying on natural forces and materials to temper air and significantly improve comfort.

The turn of the 20th century saw a sharp change in the trajectory of ventilation design, relying increasingly on mechanical ventilation and air conditioning. These systems have been the driving force behind architectural efforts to seal buildings, avoid leakage and minimise the energy associated with heating and cooling. The aim has been to maintain tight control on thermal comfort while the fresh air component becomes diluted and difficult to adjust.

In recent years, however, the concept of the “breathable building” has experienced a resurgence. Accelerated by the challenges and stark impacts of COVID-19, there has been a rapid paradigm shift in how building designers consider the interface between indoor and outdoor spaces and the control of fresh air, comfort, and protection.

The following section examines the key drivers accelerating the move towards breathable buildings. These include the shifting requirements of the commercial workplace, industry advocacy, climate emergency, and occupant health and wellbeing.

Are we at a crossroads?

Before discussing the drivers for natural ventilation, it is worth reflecting on another design philosophy building momentum, particularly in North America and Oceania.

Passive House (or Passivhaus) is an approach that uses five key principles to accomplish high performance. These are:

Continuous insulation

No thermal bridges

Airtight construction

High-performance windows and doors

Fresh air ventilation with heat recovery

The discourse regarding Passive House has often incorrectly assumed that a building designed to be airtight is incompatible with natural ventilation. Some have gone as far as to suggest that Passive House buildings cannot have operable windows at all.

Based on these misinterpretations, it seems like we are at a crossroads in our pursuit of high-performance, low-carbon buildings. It may appear as though we need to choose between opening the building up to create a breathable envelope or sealing the building up to create a Passive Housecompliant structure.

On the contrary, Passive House buildings worldwide have successfully implemented facade breathability, particularly in mild climates where operable windows can provide a significant proportion of summer ventilation.

Consider for a moment the objectives of a Passive House building, which is intended to be efficient, resilient, lowcarbon, healthy, and comfortable.

Sound familiar?

We are not at a crossroads, we’re simply tasked with taking a holistic view of our project context — risks, opportunities, constraints, and drivers — and developing a solution that meets the needs of its occupants, stakeholders, and community. That might not sound so simple, but it certainly shouldn’t preclude the pursuit of natural ventilation or a Passive House solution.

To support this strategic thinking, the following sections describe the drivers that put breathability on the agenda, from human and environmental benefits to financial and policy incentives.

This page: Artist’s Impression of Central Place Sydney and Atlassian Central ©Central Place Sydney

Current drivers for natural ventilation

Occupant Health And Wellbeing

Much like biophilic design or a window view of nature, the provision of natural ventilation provides benefits to our wellbeing. Increasing outdoor air supply improves cognitive function and health by removing airborne pathogens and carbon dioxide (CO₂) released by occupants and volatile organic compounds (VOCs) released by building interiors1. It is surprising how often buildings, particularly schools, fall short of the minimum ventilation rates set out in standards such as ASHRAE 2 .

Even where code compliant ventilation is provided, these volumes are established as a minimum threshold rather than to support optimum health and wellbeing. The effects of underventilation carry a huge cost in terms of productivity and health and can lead to respiratory issues, allergies and absenteeism. Natural ventilation gives the option to boost outdoor air rates at a relatively low cost compared to the wholesale upsizing of mechanical systems.

Natural ventilation can also improve thermal comfort within buildings and the subsequent health impacts. There is mounting evidence that suggests uniform temperatures — as often found in mechanically ventilated buildings — can lead to reduced metabolism and glucose sensitivity. In contrast, natural ventilation coupled with an “adaptive comfort” design approach provides the variability in environmental conditions that is much more aligned with the needs of our body’s complex systems.

1 https://pubmed.ncbi.nlm.nih.gov/26502459/

2 https://onlinelibrary.wiley.com/doi/10.1111/ina.12403

For much of the 20th century, we have kept indoor environments as sterile as possible by sealing the building and killing any surface bacteria. There is now a growing consensus that we have been over-sterilising indoor environments, leading to an increased likelihood of asthma and allergies. Interior environments have a dynamic ecosystem of microorganisms. Some are healthy, and some are harmful3. A balanced culture of microorganisms in our built environment is necessary for human health. It is a challenging field to define because it must be balanced against preventing the spread of harmful pathogens, but in both cases, the provision of natural ventilation is beneficial.

Climate Resilience

Breathable buildings make for more resilient occupants, and the same is true for the buildings themselves. The inclusion of mixed-mode systems (i.e. the option to bring in natural ventilation to alternate with, or top up, mechanical systems) makes buildings inherently more adaptable and equipped to manage a host of possible events that may occur.

The past few years have been something of a portent in terms of climate change, consistently breaking records around the world, only to be rebroken a year or two later.

When we talk about designing a resilient building, the list of considerations is growing longer. In addition to heat waves and rising average temperatures, unusual weather has increased the likelihood of extreme storms and blackouts, wildfires are

3 Anthes, E. (2020) The Great Indoors. Scientific American / Farrar, Straus and Giroux becoming commonplace across ever larger regions. Add to this the rising costs of energy, exacerbated by fuel shortages and geopolitical conflicts, and it is clear that building resilience is an urgent necessity.

When a building has multiple modes of operation, both passive and active, it provides flexibility to adapt over time and to weather short-term aberrant events. By balancing this with reducing energy consumption over the lifespan of a building and limiting the CO₂ released into the atmosphere, we can help slow the global warming causing these extreme events.

The Modern Workplace

The commercial sector is evolving4. The shift to hybrid work following COVID-19 and its associated economic slowdown has caused companies, developers, and architects to rethink the modern workplace.

Employees are also demanding sustainable and healthy workplaces with better amenities , and there is increasing evidence that these features facilitate heightened productivity and improved staff retention rates. For most businesses, the financial expense associated with staff far exceeds outgoings for rent or energy bills, so the case for a people-first approach to workplace design is compelling.

For companies of all sizes, the challenge is to provide flexible and desirable workplaces to attract and retain the best

4 https://www.economist.com/finance-and-economics/2021/06/03/ what-a-work-from-home-revolution-means-for-commercial-property workers and bring them back into the office. In Australian capital cities, the current high occupancy rates in Central Business District (CBD) office buildings are giving flexibility to companies who are out of lease to move to higher-grade, better-provisioned tenancies.

The pressure is on developers to provide these types of sustainable and healthy commercial products to retain and attract anchor tenants as well as smaller-scale leases . This includes flexible office space that can be used as co-working zones or informal meeting and event spaces.

Even within larger tenancies, flexibility and a range of spaces within a workplace fit-out have driven a requirement for an equal level of flexibility and adaptability of the building systems and fabric.

Industry Advocacy

We are experiencing a swell of advocacy for healthy, resilient buildings among designers, engineers, industry bodies and institutions. Project teams, particularly in market segments where natural ventilation is less prevalent (e.g., new commercial buildings), are proposing breathable buildings more often than they were at the turn of the century.

One current focus area is reducing building material embodied carbon. The publication of the CIBSE Technical Memorandum 65 ( TM65)5 in 2021 has cast a light on the quantification of building services equipment embodied carbon, which drives 5 https://www.cibse.org/knowledge-research/knowledgeresources/engineering-guidance/technical-memoranda/tm65an-internationally-applicable-methodology-for-the-calculationof-embodied-carbon-in-building-services-engineering-alt advocacy for the minimisation of HVAC equipment. This in turn drives appetite for mixed-mode or naturally ventilated buildings, creating incentive for all building design disciplines to ensure their knowledge of breathable buildings is in line with best practice.

Building certification schemes such as LEED, BREEAM, Green Star, Passive House/Passivhaus, and WELL align incentives to desired outcomes (such as improved ventilation) rather than rewarding specific approaches (such as natural ventilation). This technology-agnostic approach is a good thing; it reduces the risk of undesirable outcomes by avoiding prescriptive incentive schemes that promote a singular solution. Here are some examples:

France’s environmental standard ES RE2020, in force from 2022, mandated that 30% of the surface area of vision glazing must be operable. While well intentioned, the requirement has been typically side-stepped with loopholes. This often ends up adding cost without providing the benefits of natural ventilation

Vancouver and the province of British Columbia will introduce a 26 °C indoor air temperature limit in 2025 to avoid heat deaths. The policy has been criticised as it is expected to promote pushing costly and carbon-intensive active systems at the expense of passive and performancebased solutions

The London Plan, prior to the advocacy of the LETI and others, incentivised combined heat and power (CHP) technologies, even though they were higher carbonemitters than alternative solutions