Sustainability in Architecture: Why Life Cycle Assessment Starts at Concept

Most architects don't lose the sustainability battle at the detail. They lose it at the napkin sketch.

By the time a project reaches working drawings, the three decisions that drive most of a building's carbon, its form, its structure, and how much of it is glass, are already locked. You can specify low carbon concrete and triple glazing all you want at that point, but you are optimizing inside a box someone else drew months ago. That is the uncomfortable truth that life cycle assessment (LCA) makes visible, and it is why "when do we start thinking about sustainability" is the most important question on a project, not the greenest.

This guide covers what LCA actually measures, where it belongs in the phases of service under the Canadian Handbook of Practice for Architects, how it reshapes design decisions, and what it costs you when you bring it in too late. It's relevant whether you're running a project or studying for the ExAC, because "Energy Literacy/Sustainability" is now its own logged competency in the Internship in Architecture Program, and the thinking shows up squarely in Section 1, Design.

What is a life cycle assessment in architecture?

A life cycle assessment is a standardized accounting of a building's environmental impact from cradle to grave: raw material extraction, manufacturing, transport, construction, the decades of use, and eventual demolition or reuse. It's governed internationally by ISO 14040 and ISO 14044, and the European standard EN 15978 gives the building-specific structure most practitioners recognize, the familiar A (product and construction), B (use), C (end of life), and D (beyond the boundary) life cycle stages.

In plain terms, an LCA tallies up everything that goes into a building, the inventory, and multiplies each quantity by its environmental impact. The Life Cycle Assessment of Buildings: A Practice Guide uses a deliberately simple example. 100 kg of steel at roughly 0.43 kg CO₂e per kg gives you about 43 kg CO₂e, and 50 kg of glass at roughly 1.06 kg CO₂e per kg gives you about 53 kg CO₂e. Do that for every assembly, sum it, and you have the building's footprint. (Notice that the glass already produces more emissions than the steel per unit weight. Hold that thought for the glazing section.)

LCA tracks five well-established impact categories:

GWP gets the headlines, but a real LCA reports across all five, and that breadth is the point. It stops "sustainable" from being a vibe and turns it into numbers you can defend.

Why this is now a Canadian compliance issue, not just a values exercise

Here's what changed. In Canada, LCA quietly moved from "nice to have" to "you may not get the permit, the refund, or the federal contract without it."

Federally, the Treasury Board's Standard on Embodied Carbon in Construction, first effective December 31, 2022 and significantly expanded with requirements that took effect September 1, 2025, now requires that major federal buildings (new construction over roughly 2,000 m², renovations over roughly 4,000 m²) estimate their embodied carbon through whole building LCA at both preliminary and final design, and demonstrate either a 30% reduction against a baseline or the maximum reduction achievable within a 2% construction cost premium. Concrete and structural or reinforcing steel now carry their own disclosure and reduction requirements. Notably, the architect of record can be the one to sign an exemption rationale, which means it lands on the practitioner, not just the engineer.

Municipally, the City of Toronto's Toronto Green Standard (TGS) Version 4, in effect for new development applications since May 1, 2022, caps upfront embodied carbon (the A1 to A5 stages, cradle to substantial completion) for higher tiers. For mid- and high-rise residential and non-residential buildings, Tier 2 sets a cap around 350 kg CO₂e/m² and Tier 3 tightens it to roughly 250 kg CO₂e/m², using the Canada Green Building Council's Zero Carbon Building methodology. Tier 1 is mandatory through planning approval, and the higher tiers are voluntary but tied to development charge refunds, so "voluntary" still has real money attached, and the lowest threshold drops every few years until the standard reaches near zero.

The takeaway for the design team is blunt. Regulators are asking for the LCA during design, when there's still something to change. That single fact reframes the entire timing question.

Where sustainability lives in the phases of service

The Canadian Handbook of Practice for Architects (the CHOP) structures architectural services into a sequence you know well: functional programming, then schematic design, then design development, then construction documents, then construction administration. Sustainability isn't a phase. It's a thread that runs through all of them, but it has to be picked up at the first one to be worth anything.

Map it against two curves and the whole argument becomes obvious. As a project moves forward, your ability to influence outcomes falls, while the cost of making changes rises. They cross early. Everything decisive happens to the left of that crossover.

Here's how the carbon conversation should track the phases:

Notice where the leverage sits. By the time you reach the phases where most of the fee is spent (design development and construction documents), most of the carbon is already committed.

When should you start? In functional programming. Not later.

The cleanest answer: the LCA's goal and scope should be defined in functional programming, and the first real model should run in early schematic design.

This isn't arbitrary. An LCA's reference study period (is this a 50-year building or a 100-year building?) changes the results materially, and that's a programming-stage decision tied to the client's brief and the required service life. The certification target, which determines which LCA methodology and which caps apply, is also a programming decision. If you haven't had the sustainability conversation by the time you're sketching massing options, you're choosing a structural system and a glazing ratio blind to their single biggest consequence.

LCA is also iterative by design. You model, you find the hot spots (the assemblies driving most of the impact), you change the design, and you model again. Change the structure from concrete to steel and you've also changed the thermal behaviour of the envelope, which changes the insulation, which changes the model, so you run it again. That loop only works while the design is still soft. Start it in design development and you're not iterating, you're filing a report.

What sustainability actually changes: form, structure, and glazing

This is where it stops being abstract. Three early decisions carry most of the weight.

Form and massing

A building's shape is a carbon decision before it's an aesthetic one. A compact form with a low surface-to-volume ratio has less envelope to build (less embodied carbon in cladding, insulation, glazing) and less surface to lose heat through (less operational carbon). The articulated, jagged form covered in cantilevers that looks great in a competition render is often quietly expensive in both. None of this is fixable later, because massing is a schematic design decision, full stop. Think of it like packing a suitcase. The cube fits more with less surface than the same volume spread out into a starfish.

Structure and primary material

Structure is usually the largest single chunk of embodied carbon in a building, which is exactly why both the federal Standard and TGS zero in on concrete and steel. The swing between a concrete frame, a steel frame, and a mass timber structure is enormous, and it cascades. As the LCA practice guide points out, switching the structural material changes the envelope's thermal design, because concrete and steel behave differently, so the insulation strategy has to be reworked too. You cannot bolt a low-carbon structure onto a scheme in design development, because the grid, the spans, and the foundations are already drawn. Encouragingly, industry analysis in the Toronto market suggests reductions on the order of 30% are often achievable without changing the primary structural material at all, as long as you're looking early enough to make the swaps.

Glazing and window-to-wall ratio

Remember the glass producing more emissions than the steel per kilogram? Glazing is a double penalty. The embodied side is heavy, because glass and the aluminum framing around it are carbon intensive to produce. The operational side is worse, because glass is the thermally weakest part of most walls, so a high window-to-wall ratio drives up heating and cooling loads for the entire life of the building. A floor-to-ceiling glass tower is, thermodynamically, a building that has chosen to fight physics every day for sixty years.

Window-to-wall ratio, glazing placement, and orientation are schematic design moves. Get them right early and you can daylight the interior, capture useful winter solar gain, and shade out summer heat, all passively, for free, for the life of the building. Get them wrong and you spend the next six decades buying your way out of it with mechanical systems. (In Toronto, glazing decisions now also intersect with bird-friendly design requirements, which is one more reason to settle them in schematic design rather than discover them in permitting.)

What happens if you think about it too late

The short version: late sustainability is expensive, weaker, and can fail compliance outright. Specifically:

• You can only reach the leftovers. Once structure, form, and glazing are fixed, the only levers left are marginal: a slightly better mechanical system, more insulation in a cavity that's already sized, solar panels to offset emissions you didn't need to create. You're treating symptoms.
• Redesign cost spikes. That influence-versus-cost curve is unforgiving. A change that's a pencil stroke in schematic design becomes a coordination nightmare across five consultants in construction documents. Most teams, facing that, simply don't make the change, and the carbon stays in.
• You can miss compliance and money. If a federal project needs a whole building LCA at preliminary and final design, or a Toronto project is chasing a Tier 2 or Tier 3 development charge refund, "we'll look at sustainability later" can mean failing the requirement, forfeiting the incentive, or a painful resubmission to City Planning.
• The LCA stops being a design tool and becomes paperwork. Run at the end, it documents a decision you can no longer change. Run at the start, it makes the decision better. Same tool, completely different value, decided entirely by timing.

The mental model worth keeping: sustainability brought in early is design. Brought in late, it's compliance and cost. The work is the same. The leverage is not.

How an LCA actually runs on a project

For interns who have never seen one executed, the workflow is a five-step loop, straight out of ISO 14044 and the building-specific practice guide:

1. Define goal and scope. What are you assessing, over what lifespan, against which benchmark or standard? (Programming.)
2. Collect the inventory. Quantities of every material and process. (Schematic design into design development, and this is where a coordinated BIM model earns its keep.)
3. Perform the impact assessment. Usually with software (One Click LCA, the Athena Impact Estimator, and similar) that maps quantities to impacts.
4. Interpret the results. Find the hot spots, run sensitivity analysis, decide what to change.
5. Report. Document for the client, the certification body, or the authority having jurisdiction.

The honest reality is that steps 1 to 4 loop. You almost never run it once.

Why this shows up on the ExAC

If you're preparing for the exam, this isn't a side topic. The Internship in Architecture Program now lists "Energy Literacy/Sustainability" as its own experience competency, right alongside schematic design and engineering systems integration, which tells you exactly how the regulators view it. It's a core skill, logged like any other.

On the exam itself, the thinking lives mostly in Section 1, Design, woven through programming, site and environmental analysis, schematic design, and design development, the same territory covered in our 25 free Section 1 practice questions. The examiners aren't testing whether you can run One Click LCA. They are testing whether you understand when environmental decisions get made and what they cascade into, which is precisely the form, structure, and glazing logic above.

Slot it into your prep with the 12-week study schedule, and if you're triangulating against the US system, our ARE versus ExAC comparison covers why Canadian-specific sustainability content (federal embodied carbon rules, the Toronto Green Standard, the CaGBC) doesn't appear in American prep at all. That's a real gap if you've only studied with US tools. Also worth a look: what changed on the 2026 ExAC.

Sources

This article draws on the Carbon Leadership Forum and UW College of Built Environments' Life Cycle Assessment of Buildings: A Practice Guide (2019), ISO 14040:2006 and ISO 14044:2006, EN 15978:2011, the Treasury Board of Canada's Standard on Embodied Carbon in Construction, and the City of Toronto's Toronto Green Standard Version 4.

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