What Exactly Is a Zero Carbon Building? There Is Finally a Definition

The Canadian Green Building Council has a new standard that defines what exactly counts as a zero carbon building.

view of TRCA building from the parking lot
TRCA Building, Designed to the Zero Carbon Standard (V1).

ZAS Architects

We are in a carbon crisis. According to the science behind the Paris Agreement, we need to keep global heating under 1.5 degrees Celsius (3.6 degrees Fahrenheit), and we have a maximum total carbon budget of about 420 gigatonnes of carbon dioxide equivalents (C02e). We are pumping out 40 gigatonnes per year now, which means we have to cut all of our carbon emissions really quickly. This includes reducing and eliminating operating carbon emissions—those that come from burning fossil fuels to move our cars, heat our buildings, and generate much of our electricity.

But it also includes embodied carbon, or what I have called "upfront carbon emissions"—the CO2e emissions from making the steel, concrete, aluminum, and all the materials that all our stuff is made of. It all counts against that carbon budget ceiling. It's why we have to measure it and deal with it in everything from our phones to our cars to our buildings.

This is why the new Zero Carbon Building Standard Version 2 developed by the Canadian Green Building Council (CaGBC) is such an interesting model. It takes embodied carbon very seriously. They define a Zero Carbon Building:

"A Zero Carbon Building is a highly energy-efficient building that produces on-site, or procures, carbon-free renewable energy or high-quality carbon offsets in an amount sufficient to offset the annual carbon emissions associated with building materials and operations."

different carbons


The emissions associated with building materials are what we have been calling upfront carbon emissions.

A point we keep trying to make on Treehugger is the timing of carbon emissions—the fact that with a rapidly depleting carbon budget, emissions happening now or in the next few years are important. CaGBC puts into their document what we have been saying for years:

"Embodied carbon emissions represent approximately 11% of all energy-related carbon emissions globally. Furthermore, emissions that occur during the production and construction phases, referred to as upfront carbon, are already released into the atmosphere before the building is operational. Given the timeframe for meaningful climate action is shrinking, there is a growing awareness of the critical importance of addressing embodied carbon."
Different carbons


However, where I suggested all embodied carbon should be renamed upfront carbon, the CaGBC is much more sophisticated. Upfront carbon breaks down to the product stage (including raw material supply, transport, and manufacturing) and also the construction stage (including transport, construction, and installation). With cars or phones, this might be considered the assembly stage, where all the manufactured components are put together.

Upfront Carbon


This is again why it is so important, as buildings or any product become more efficient, managing the upfront carbon becomes dominant. It's why I proposed my rule of carbon in an earlier post:

"As we electrify everything and decarbonize the electricity supply, emissions from embodied carbon will increasingly dominate and approach 100% of emissions."

The CaGBC also defines and includes "use-stage embodied carbon," which includes maintenance, repair, and replacement, as well as "end of life stage," including deconstruction, transport, processing, and disposal. I have never planned that far ahead, but it has to be estimated because it gives you a full life-cycle analysis (LCA).

Designers can leave our recycled and reused materials from their LCA, but everything else goes into it.

"The LCA must include all envelope and structural elements, including footings and foundations, and complete structural wall assemblies (from cladding to interior finishes, including basement), structural floors, and ceilings (not including finishes), roof assemblies, and stairs. Parking structures are to be included."

And then it gets interesting because all of that embodied carbon has to be offset.

"After minimizing embodied carbon emissions during design and construction, projects that achieved ZCB-Design v2 will be required to offset their embodied carbon to achieve ZCB-Performance certification. As outlined in the ZCB-Performance Standard, projects may choose to mitigate embodied carbon by offsetting equal amounts annually over as many as five years."

These have to be real, quality carbon offsets, certified by Green-e Climate or equivalent. Many roll their eyes and the idea of offsets, but there are legitimate ones that have safeguards to ensure:

  • Additionality: The likelihood that the emissions reductions would not have happened anyway.
  • Permanence: The likelihood that the emissions reductions will not be canceled over time.
  • Leakage: The risk that emissions reductions will result in increased emissions elsewhere.

As an example, Gold Standard carbon offsets cost between $12 and $22 per ton of CO2e; this could make steel or concrete buildings more expensive and could make underground parking garages very expensive indeed.

In fact, I wondered if anyone would even use this standard because of the cost of those offsets. Architect Sheena Sharp, who was on the CaGBC Zero Carbon Steering Committee, tells Treehugger: "They won't have a choice. Municipalities across the country are demanding compliance with the Zero Carbon Standard in their Requests for Proposals."

At least they are until the suburban city councilors find out how much their underground parking stalls are costing them in offsets. As Ron Rochon of Miller Hull (they are offsetting their own buildings) admits to Treehugger: "The cruel truth of architecture is that parking often drives the design."

Then there was the study done by Kelly Alvarez Doran of the John H. Daniels Faculty of Architecture, which found underground parking and foundations were responsible for as much as half of a building's carbon footprint.

This is why I remain concerned that embodied carbon will continue to be the issue nobody wants to talk about or deal with: it is almost impossible to disentangle it from our dependence on the automobile. I suspect it will be the biggest limitation on acceptance of this standard.

Wait, there's more!

The CaGBC Zero Carbon Standard is no slouch when it comes to operating energy and emissions.

"Projects pursuing ZCB-Design certification must demonstrate superior energy efficiency. Energy efficiency is critical to ensuring the financial viability of zero-carbon designs, promotes resiliency, frees clean energy for use in other economic sectors and geographical regions, and reduces environmental impacts from energy production."

It offers different pathways to zero emissions and "three different approaches are available to demonstrate energy efficiency."



There's a lot more that promotes innovation, that anticipates climate changes, that addresses peak demand; it is complicated and thorough.

There is much to learn from this. Sharp tells Treehugger that it is not like LEED covering a bit of everything, but that it is singularly focused on energy and more particularly, carbon dioxide and its equivalents. If we are going to have any success at all in delaying the total blowout of the carbon budget, this is the kind of focus we all need.