Buildings are massive emitters. Their heating, electricity and construction cause about 10 billion metric tons of CO2 per year worldwide. On average, that's about 1.3 tons of carbon dioxide per person every year. 

In 2021, the buildings and construction sector was responsible for 37% of energy-related CO2 emissions, surpassing the transportation sector (22%), according to a UN study.

So how can we reduce these high emissions? And what measures can we take to ensure sustainable, affordable and comfortable living?

More housing, more CO2

The world's population has grown significantly over the past 100 years, and so have housing needs. And, as income levels have soared, there has been a rise in the number of people living alone. But across the world, there are huge variations in the amount of living space. 

A person in Nigeria, for example, uses 6 square meters (65 square feet) of living space on average. That number goes up to 18 in Turkey, 24 in Brazil, 30 in China, 38 in the European Union and 75 square meters in the United States. 

In Germany, the average living space per person has more than tripled since 1950 ⁠— rising from 15 square meters to 48. Older empty nesters tend to have the most room, with senior citizens having an average of 60 square meters per person.

The more apartments and houses there are, the more energy is needed for heating and electricity — and the more CO2 is produced by these new buildings.

Older buildings need a particularly high amount of energy for heating, which can become expensive. But they can save up to 90% of energy with insulation and modern ventilation systems. And heating costs can also go down if less room is used.

How do we heat affordably in a climate-neutral way?

Biogas, wood or wood pellets are a few climate-friendly alternatives to fossil fuels. But these resources are becoming increasingly scarce and expensive, so experts also recommend heat pumps. These draw heat from the ground or air and are powered with electricity. They can generate up to 7 kilowatt hours (kWh) of heat energy from 1 kWh of electricity.

Heat pumps do not produce harmful particulate matter and, if green electricity is used, no CO2. In Scandinavia, buildings have long been heated with heat pumps and district heating is operated with large ones. In combination with solar thermal energy, biomass and deep geothermal energy, some of these networks are close to being climate-neutral.

Producing your own solar power

Energy-efficient heat pumps, fridges and LEDs can also lower the power consumption of buildings. Affordable electricity can even be generated at the house itself with photovoltaic roofs and facades. 

In Germany, solar panels for the roof can generate solar power for less than 0.10€ ($0.11) per kWh. That's not even a quarter of the price one would normally pay for electricity from the grid: an average of 0.40€ per kWh. Solar panels pay for themselves in five to 15 years, after which they generate free electricity for around two decades. 

Renewable material instead of concrete, steel and plastic

A lot of CO2 is emitted during the construction of buildings, some 0.5 to 0.8 tons per square meter of living space. That's about 50 to 80 tons of CO2 for the construction of a new 100-square-meter apartment. In comparison, India emits 2 tons of CO2 per capita per year.

Emissions are mainly caused by the production of cement, lime and gypsum (25%), by the construction itself (10%) and by the production of building materials such as insulation (8%) and metals (8%).

Alternative building materials such as wood and renewable insulating options like straw can drastically reduce CO2 emissions from construction sites. In Germany, it could slash them by 50%.

Refurbishing instead of building

Upgrading older units instead of building new ones also saves CO2 and reduces expenses. Renovation usually costs around a quarter less than building a new building, meaning emissions from construction and operation can be more than halved. 

That's why architects, scientists and environmental associations want city planners and builders to rethink their designs. They say demolition and new construction should be avoided wherever possible, and refurbishing older buildings should become the norm. 

Less living space to protect the climate?

Considering the housing shortage and the climate crisis, experts also want society and politicians to rethink their priorities.

"The area of land on which people in Germany live today would be sufficient for 200 million people ⁠— if they were content with an area that was common in the 1960s," said sociologist Maike Böcker of the Institute for Cultural Studies in Essen, in western Germany. 

Germany currently has a population of 83 million people; in 2022, the global population surpassed 8 billion.

In a 2020 study, the Wuppertal Institute for Climate, Environment and Energy called for "intelligent and flexible" ways of using living space. The German think tank said this is necessary to curb growing demand and keep global heating to 1.5 degrees Celsius (2.7 degrees Fahrenheit).

Meanwhile, Austria's Graz University of Technology has modeled a scenario in which global energy demand falls by 40% ⁠— despite the growing population ⁠— to comply with the 1.5-degree limit. The researchers recommend a worldwide average of 30 square meters of living space per person.

More social contacts for better living

Experts also see potential for senior citizens to cut down on living space. In industrialized countries like Germany, many older single people or couples live in large apartments or houses after their children move out, though these homes are often not equipped to meet the needs of the elderly. At the same time, there is a lack of living space for young families, especially in cities.

This is where targeted advice and offers can help, according to urban planner and economist Daniel Fuhrhop. 

"They could move into smaller apartments or renovate their homes to add an additional dwelling unit," he said. "They could also sublet or live with other people. There are many great, tried-and-tested options."

Some universities now arrange for students to pay lower rents by living with seniors and helping them with household chores. Housing projects with small, individual living units paired with communal gardens, workshops, studios as well as laundry and fitness rooms are also becoming increasingly popular.

In this model, office space and guest rooms can be booked for a certain period of time at a reasonable price. Many residents appreciate these shared quarters. It's a way for them to spend time together, get to know each other better and to support each other.

This article was originally published in German.