New research from the School of Architecture, Design and Planning warns apartments built to today's standards could become dangerously hot by 2050, prompting calls for urgent reform of Australia’s building codes.

Sydney apartments built to today's standards could become dangerously hot by the middle of the century, with residents in some areas facing weeks of indoor temperatures above safe comfort levels, according to new research published in Energy and Buildings.

The University of Sydney-led study, Are code-compliant buildings ready for future climate? A case study of thermal autonomy in Australian apartments, found, under future climate scenarios, apartments built to comply with Australia's current National Construction Code could experience a dramatic increase in indoor overheating. Top-floor apartments and those in Western Sydney are particularly susceptible.

The findings come as Sydney undergoes rapid rezoning and apartment construction and highlights a growing inequality. Using the latest high-resolution climate-projections for New South Wales, the research modelled apartment buildings in inner-city Redfern and Western Sydney’s Penrith. Results showed residents in Western Sydney could experience almost twice the indoor overheating risk of residents living closer to the coast.

"Australia is building homes for the future using standards designed for the climate of the past," said lead researcher Dr Shamila Haddad from the School of Architecture, Design and Planning.

“By the 2050s, median outdoor temperatures in Sydney's hotter inland areas could rise by up to 5°C under high-emissions climate scenarios, with hot days becoming longer and more frequent,” said Dr Jingjing Liu from the School of Architecture, Design and Planning.  

Under these conditions:

• Apartments built to current standards could be too hot for comfort for the equivalent of around four weeks a year in Redfern and more than seven weeks a year in Penrith.

• Indoor overheating risk increased consistently across all climate projections tested.

• West-facing and top-floor apartments were particularly vulnerable because of low-angle afternoon sun and solar heat absorbed through roofs.

• During extreme heat events, under the high-emission scenario, indoor temperatures could remain above 30°C for several consecutive days.

The findings have significant implications for public health, especially during prolonged heatwaves and potential power outages.

"In a future heatwave combined with a blackout, many apartments simply won't be able to keep residents safe," said Dr Haddad.

Heat stress is an increasingly important issue for the health and well-being of populations exposed to high temperatures and humidity. 

"People often assume air conditioning (AC) will solve the problem, but not everyone can afford to install or run air conditioning due to cooling poverty, and during power outages, it may not be available. 

“Also, while AC can provide relief against heat stress, widespread use of AC can add pressure on electricity systems and even more heat to our cities,” said Dr Haddad.

Older people, low-income households, renters and people with chronic health conditions are expected to be among those most vulnerable.

The research argues that Australia's building regulations should move beyond measuring energy efficiency based on historical weather data and instead assess a building's "passive survivability" - its ability to maintain safe indoor temperatures during extreme heat without relying on air conditioning.

Passive building strategies, including cool roofs, natural ventilation, and shading have proven to be effective in improving cooling comfort, while typically being affordable solutions.

The study found relatively straightforward design changes could dramatically reduce future overheating risks, including:

• External window shading, which reduced overheating by up to 32 per cent;

• Safe night-time ventilation, which reduced overheating by up to 34 per cent;

• Lighter-coloured roofs to protect top-floor apartments; and

• Insulation and double glazing.

• In combination, these measures could reduce overheating risk by up to 94 per cent.

The study calls for building standards to require new apartments to be tested against future climate scenarios and to establish minimum performance requirements for homes during extreme heat events.

"Australia urgently needs more housing, but we also need homes that remain safe and liveable," explained Dr Haddad.

"If we're designing cities for 2050, we need to start designing buildings for the climate of 2050."