The hidden emissions in basements
The Emissions Hidden in Basements
Basements might not get much attention in a building’s design, but when it comes to embodied carbon, they deserve a closer look. Whether they're used for car parks, plant rooms, or utilities, basements come with a significant carbon footprint that’s often overlooked. Let’s break down why going underground can seriously bump up emissions.
Why Basements Carry Heavy Hidden Emissions
The main culprits for high embodied carbon in basements are simple: lots of concrete and plenty of excavation.
Basements use thick concrete for external walls (sometimes up to 400 millimetres thick!) and internal walls, plus a fully encased concrete structure to hold back both soil and water.
Unlike above-ground spaces, all that digging requires serious machinery, which means more emissions before you even pour the first slab.
That means while basements might not look like much from the outside, what's required to hold them up and keep them dry comes with a heavy environmental cost.
Why Choose Basements, Anyway?
Despite their hidden carbon costs, basements are a popular design pick for a few practical reasons:
Basements are often a cost-effective way to add space than expanding above ground
Basements are a common choice for parking, plant rooms, or utility systems
Decorative finishes are seldom needed, keeping costs down
But Tom Dean, Director of Carbon Planning at Slattery, cautions against relying too heavily on basement spaces:
“Every extra metre underground means a lot more concrete and a lot more carbon.”
Put simply, basements help maximise site value in a cost-effective way - but they come with a larger materials footprint than above-ground options, and it's worth weighing up those trade-offs.
The dilemma with basement parking
Car parking is a great example of how the placement of a function can change the carbon story—and pose trade-offs for designers and planners.
From an urban design perspective, basement parking has clear advantages. By putting cars below ground, podium levels can be used for more active, people-friendly uses, like shops, cafes, offices, or homes. This helps create safer, more engaging streets with more “eyes on the street” and encourages walkable, vibrant neighbourhoods.
But from a carbon perspective, the picture is less ideal.
Basement parking uses significantly more concrete than above-ground options due to the need for thick retaining walls and full structural encasement
The excavation process also adds high emissions from fuel and heavy machinery
Studies show that above-ground parking can use roughly half the embodied carbon of its basement equivalent
So while basements make sense from a density and design point of view, they come with a carbon cost that’s easy to overlook. It’s not a cut-and-dry answer. Just one of many trade-offs in balancing climate goals with liveability and good design. Understanding that tension is the first step to making more informed choices.
