Karim Allana
4 min readDec 14, 2023


Buildings & Construction Account for One-Quarter of Global Greenhouse Emissions — But They Don’t Have to. Here’s How.

A recent U.N. report finds that building construction and operation accounted for 37% of “energy and process-related” carbon emissions in 2021. The sector’s overall share of human-caused greenhouse emissions is lower, at 25%. But that’s still one-quarter of humanity’s total planet-warming emissions.

We can’t decarbonize without the built environment. Fortunately, we know how to shift to a low- and eventually zero-carbon scenario. It’ll take decades, yes, and trillions of dollars in new investment. But we’re up to the task.

Designing Through a Sustainable Lens

McKinsey’s detailed report on building decarbonization contains an oft-overlooked bit of wisdom: “By the time the construction process begins, the majority of decisions affecting the project’s GHG emissions are locked in.”

For builders and operators focused on low- or zero-carbon impact, this means design choices are absolutely critical. The optimal time to set a building on a sustainable pathway is before construction begins.

In the U.S., sustainable builders generally follow LEED standards when choosing building materials and designing systems. Some integrate Passive House standards into building design as well. The two standards complement each other, with LEED more of a big-picture approach and Passive House focused on energy conservation.

These standards aren’t all-encompassing. Increasingly, we’re seeing novel design elements in “mainstream” construction, such as reflective or green roofs that reduce daytime cooling loads.

Making the “Fuel Switch” in Building Heating & Cooling

Direct operational activities, such as heating and cooling, account for 69% of total building emissions, according to McKinsey. Switching from higher- to lower-carbon fuel therefore is very often the single most important carbon-reduction step building owners and builders can take.

In existing buildings, fuel-switching requires significant upfront investment and may bring logistical challenges. While changing out an aging oil boiler for one that runs on natural gas can reduce a building’s carbon load and should pay for itself before the new boiler fully depreciates, that payoff date generally takes years to arrive. Switching from oil or gas to efficient electrified heating and cooling (which these days invariably means installing a heat pump) offers even greater decarbonization benefits, but if the switch involves installing new forced-air ducts, the upfront cost can be prohibitive.

To be clear, building owners should still invest in lower-carbon HVAC systems. They just need to be realistic about what that entails and budget accordingly.

Taking Care of the “Boring” Stuff

While fuel-switching major appliances offers the greatest carbon-mitigation impact in existing buildings, even more “boring” changes can make a difference too.

Insulation is the lowest-hanging fruit in this category. According to McKinsey, bringing a “low insulation” building to “medium insulation” standards can reduce energy demand by up to 20%. This is usually a “cost positive” improvement, meaning it pays for itself over a reasonable period of time.

Addressing the Material Elephants in the Room

Materials account for about 28% of overall building and construction emissions. Within this category, the two biggest offenders are steel and cement, both of which require carbon-intensive manufacturing processes that aren’t easily abated.

A low hanging fruit in this category is life expectancy of building assemblies. Roofing systems can last 40–50 years, but most don’t. In the last 3 decades, average life span of roofs has increased from 16.5 years to about 20 years, but well below its full potential. Due to poor quality of built construction or selection of materials that are not durable, large volume of roofing and and façade elements are replaced prematurely. Average life expectancy of buildings in the US is less than 50 years, whereas life expectancies of buildings in Europe is well over 200 years. Increasing life expectancies of building is very achievable by durable construction practices which can greatly reduce the carbon footprint.

Despite recent advances, carbon-neutral cement production and steelmaking are many years from cost parity with status-quo methods. For now, builders should look to reduce embodied emissions using lower-carbon recycled steel and concrete wherever possible while substituting lower-carbon structural materials (such as mass timber) if and when building design allows.

Final Thoughts

The construction industry has a reputation for risk aversion. Building contractors and experts tend to be skeptical of new technologies, new materials, new processes, at least until it’s clear that they improve on the old versions. New materials are not necessarily longer lasting or more durable. Selecting building assemblies and systems that have a proven track record of longevity may still be the best option. Performing 3rd party quality control and testing during construction can have a huge impact on cutting down premature construction failures and greatly improve longevity in construction assemblies.

And for good reason. When your business is designing and building structures to last for decades, the stakes couldn’t be higher.

However, if we’re truly committed to decarbonizing the economy by the middle of the 21st century, building owners and contractors must be willing to spend more money for quality assurance to build longer lasting construction assemblies. Turning the ship — or crane — will take years, and we don’t have much time to spare.



Karim Allana

Karim Allana is founder and CEO of Allana Buick & Bers. He is an industry leader in building envelope architectural engineering and construction management.