A building's lifetime climate impact is mostly determined by its daily energy use.

The majority of a building's climate impact is not caused by its construction. As the heating, lighting, and ventilation systems continue to function year after year, it gradually accumulates.

How unbalanced that balance can be is demonstrated by a digital analysis of an office block in northern China. Rather than building materials, daily operations accounted for over 95% of the building's lifetime carbon output.

Before building started, the team, led by Dr. Yujing Yang of Shanxi University (SXU), calculated emissions using computerised design techniques.

The goal was to incorporate carbon accounting into the design phase, where long-term emissions can still be influenced by choices made concerning heating systems, materials, and insulation.

Combining carbon and design

The team can extract precise quantities for major materials using Building Information Modelling, a data-rich 3D project model that complies with industry standards.

An ISO standard that establishes common counting guidelines is followed by life cycle assessment, a standardised method of totalling impacts across stages. Carbon dioxide equivalent, a popular metric that adds gases by warming power, was used to report the results.

The procedure was evaluated by the researchers on a three-story office building that was roughly 13,445 square feet (1,249 square

Structures seal off emissions

According to a United Nations Environment Programme research, buildings were responsible for 37% of the world's carbon dioxide emissions related to energy and processes in 2022.

Between 2005 and 2020, China's construction-related emissions more than doubled to 5.60 billion short tonnes (5.08 billion metric tonnes).

Because every new structure locks in climate impacts related to materials and energy use for decades, this growth increases the significance of design-stage decisions.

Instead of looking for reductions after concrete has set, teams may compare choices early thanks to detailed model output.

The material's hidden cost

The pollution from producing and transporting materials before a building's opening is known as embodied carbon, and it is the main source of upfront emissions.

Steel reinforcing outpaced concrete and cement in the model, accounting for 46% of material-production emissions in the case construction.

Because limestone produces carbon dioxide when heated to become clinker for concrete mixtures, cement increases the pressure.

Heavy material transportation

When materials are heavy, transportation can compete with production. Sand, one of the heaviest common elements, is particularly affected by truck mileage.

Sand transportation accounted for 40% of the study's transportation emissions, despite the fact that sand production itself had a negligible contribution.

Based on baseline estimates, multiple bulk commodities were transported approximately 311 miles to the location, increasing fuel consumption with each trip.

Improved material standards can lower embodied emissions, but the biggest benefits rely on what local suppliers and manufacturers can actually provide.

According to Yang, "our findings show that transportation distance can matter just as much as the material itself."

The largest increases are driven by operations.

Once a structure is occupied, daily energy use becomes the primary source of emissions, particularly in colder climates. Since coal provided the majority of the heat in Taiyuan, heating-related emissions accounted for approximately two-thirds of operational emissions.

Improved insulation reduces demand by preventing leaks in the first place because heat loss via windows and walls makes boilers and pumps work harder. Even tiny efficiency gaps accumulate over a 50-year design life, making retrofits significantly more challenging and costly than acquiring

Changing the source of heat

These totals change as the heat source is changed. By replacing coal with ground-source heat pumps, which draw consistent heat from the earth, overall life-cycle emissions can be reduced by roughly 19%.

Because heat pumps transfer heat instead of producing it, they change the equation and provide more useful energy per unit of power. Although the advantage is dependent on methane leaks and the carbon intensity of the local gas supply, natural gas heating also decreased emissions.

The same equipment becomes cleaner over time as energy generation moves towards lower-carbon sources because electric systems also monitor the power grid.

Making adjustments to reduce emissions

Sensitivity analysis, a test that modifies one assumption at a time, was employed in the study to demonstrate which levers are important.

In a combined scenario, switching to lower-emission trucks and closer suppliers lowered transport emissions by 73.9%. This outcome resulted from reducing emissions per mile and reducing long hauls to around 31 miles (50 km) for a number of goods.

Builders want local information on fleets, roads, and supplier locations because real projects could not match those inputs.

Considering carbon when designing

The study demonstrates how climate data may be included in digital design files from the outset, allowing building design teams to select heating systems, improve building envelopes, and choose materials before bids are sent out.

Since transportation distance is explicitly reflected in the totals, developers can support those decisions with procurement policies that support regional supply chains.

By establishing a uniform system boundary—a distinct line around what is counted—city officials may use the same accounting in permits to compare projects equitably.

The study's most important practical lesson is to use local data and better possibilities to minimise materials and transportation emissions after reducing a building's long-term energy demand.