For years, a popular saying has guided sustainable building decisions: “The greenest house is the one that is already built.” The logic seems sound. Retrofitting an existing structure avoids the upfront carbon cost of demolition and new construction. But a detailed study by Waymark Architecture and Energy Code Solutions challenges this assumption with real data. Their analysis, comparing a heritage home retrofit with a new low-embodied-carbon Passive House in the same neighborhood, reveals a more nuanced picture. The findings show that while retrofits can reduce emissions, a high-performance new build with carefully chosen materials can outperform an existing home over the long term. Choosing the right approach depends on many factors, including climate zone, material selection, and the 25-year trajectory of carbon emissions. For those looking at the full environmental picture, understanding the trade-offs between different greenest wall system brick stucco eifs options is just one piece of the larger puzzle.
Understanding Embodied Carbon Versus Operational Carbon
To answer whether renovation or new construction is greener, we must first distinguish between two types of building emissions. Operational carbon is the energy used to heat, cool, and power a building over its lifetime. This is what most energy codes and efficiency standards target. Embodied carbon, on the other hand, is the sum of all greenhouse gas emissions associated with producing, transporting, and installing building materials, plus the emissions from eventual demolition and disposal. The industry has historically focused on operational carbon, but ignoring embodied carbon paints an incomplete picture.
The study compared six scenarios across multiple climate zones using consistent methodology. The key finding is that both types of carbon matter, but operational emissions carry more weight over time. A crucial insight is that the choice of wall assembly significantly affects a building’s total carbon footprint. Comparing greenest wall system brick stucco eifs comparison data shows how material decisions cascade into long-term performance. The study makes clear that ignoring either operational or embodied carbon leads to suboptimal outcomes.
The first priority should be to reduce operational emissions. A very close second priority should be to choose responsible materials.
Waymark Architecture and Energy Code Solutions study findings
The study used tools including Hot2000 for energy modeling, MCE2 for embodied carbon calculation, CIBSE calculators for mechanical systems, and HEET for yearly operational carbon extraction. Each scenario was modeled consistently across climate zones 4, 6, and 8 to capture how similar buildings perform in different regions.
The Six Scenarios That Reveal the Real Trade-Offs
The analysis featured two real projects and four hypothetical scenarios. The first real project is a registered heritage house in Victoria, British Columbia, where a careful retrofit was planned within the constraints of heritage status. The second is a new build just a block away, designed to meet the rigorous Passive House standard using low-embodied-carbon materials. This second project, called the Sugar Cube house, represents what a well-designed new build can achieve. As The Greenest House In America demonstrated years ago, building ultra-efficient homes has long been a goal of the green building movement, and today’s Passive House standard brings that vision within reach of mainstream construction.
The four additional hypothetical scenarios were constructed to isolate specific variables:
- High-embodied-carbon Passive House — The same shape and size as the Sugar Cube house but built with conventional high-carbon materials to show the impact of material choices.
- Existing home with air source heat pump — The heritage house left as-is but with its gas heating replaced by an electric heat pump.
- Existing home with baseboard heating — Gas replaced with electric baseboards, representing a minimal intervention.
- Existing home with gas furnace — The heritage house left completely unchanged, serving as a baseline reference.
Each scenario was modeled not only in climate zone 4 (Victoria’s mild coastal climate) but also in colder zones 6 and 8, with adjustments to insulation thickness and mechanical system sizing. This cross-climate analysis provides a robust picture of how the same strategies perform in different conditions.
Why Climate Zone and Timeframe Matter
One of the study’s most valuable contributions is showing how results shift across climate zones. In mild climate zone 4, the difference between a careful retrofit and a new low-embodied-carbon Passive House is surprisingly small over a 25-year horizon. After that period, the new build begins to pull ahead. In colder climate zones, the advantage of the new build becomes clear much faster. The analysis demonstrates that when evaluating wall assemblies and insulation strategies, comparing which is the greenest wall system comparing brick stucco and eifs for environmental performance provides useful data but must be paired with climate-specific operational carbon modeling to reach meaningful conclusions.
Here is a summary of the key findings across climate zones for the low-embodied-carbon Passive House compared to the retrofit scenario:
| Climate Zone | Carbon Payoff Period (LEC PH vs Retrofit) | Key Observation |
|---|---|---|
| CZ4 (Mild) | 50 years | Scenarios converge around 25 years with similar total GHGs; LEC PH pulls ahead after that |
| CZ6 (Cold) | 16 years | Operational carbon dominates; colder climate accelerates payoff |
| CZ8 (Very Cold) | 9 years | Low-embodied-carbon Passive House outperforms all options in under a decade |
The takeaway is clear: the colder the climate, the faster a high-performance new build justifies its upfront embodied carbon. The reason is that operational energy savings compound much more quickly when heating loads are larger to begin with. This has important implications for builders and homeowners in northern regions who might otherwise default to renovation as the greener option.
The Hidden Impact of Mechanical Systems and Refrigerants
Perhaps the most surprising finding concerns mechanical systems. Heat pumps, which are widely promoted as a green alternative to gas furnaces, carry their own significant carbon cost through refrigerants. Refrigerants have extremely high global warming potential, and the size of the heat pump directly correlates with the amount of refrigerant required.
In climate zone 4, the embodied carbon of the heat pump alone is nearly equal to all the building components of the low-embodied-carbon Passive House combined. In climate zone 6, the heat pump’s embodied carbon reaches 20.6 tonnes, while the entire low-embodied-carbon Passive House structure accounts for 13.4 tonnes. This means that failing to reduce operational energy demand forces larger mechanical systems, which in turn create higher embodied emissions from refrigerants. The study makes a strong point that switching fuels to electricity is only environmentally beneficial if the heating load is reduced first. Without that step, we risk what the researchers call greenwashing. Effective water conservation strategies home builders lessons from those already conserving share a similar principle: reducing demand before upgrading technology yields the best environmental returns.
The study also notes that carbon dioxide heat pumps, which are new to the market, drastically reduce the carbon impact of mechanical systems. However, these require a relatively high-performing building envelope because their output capacity is limited. This creates a virtuous cycle: better envelopes allow smaller, cleaner mechanical systems. Passive House construction naturally enables this cycle.
Making the Right Material and Design Choices
For the low-embodied-carbon Passive House scenario, the most significant carbon contributions came from concrete and windows. This finding underscores the importance of mindful material specification from the earliest design stages. Waymark Architecture made deliberate choices for the Sugar Cube house that included using concrete only where structurally necessary and placing the Passive House envelope above grade to eliminate the need for slab or foundation foams. These decisions reduced embodied carbon without compromising performance.
High-embodied-carbon building materials should always be minimized or avoided where practical alternatives exist. The study found that a high-embodied-carbon Passive House is never the right choice, even though its operational carbon is low. In climate zone 4, it takes 50 years for the reduced operational emissions to compensate for the upfront carbon investment. In colder zones the payoff improves, but the low-embodied-carbon option always outperforms its high-carbon counterpart. Even practical skills like learning how to keep your stove top clean using natural methods you already have at home reflect a broader mindset: the simplest, most resource-efficient approach often delivers the best long-term outcomes.
The study identified several key steps for reducing embodied carbon in new construction:
- Use concrete only where structurally necessary and avoid unnecessary slabs and foundations
- Select wood-framed double-pane windows as the lowest-embodied-carbon glazing option
- Eliminate foundation foams by positioning the thermal envelope above grade
- Choose locally sourced and low-embodied-carbon insulation materials where possible
- Design for deconstruction to maximize material reuse at end of life
These principles apply whether building new or renovating. In the retrofit case, the study’s triage approach improved airtightness, added attic and basement insulation, and installed an air source heat pump without major demolition. Wood-framed windows replaced the old ones since they represented the biggest heat loss path. The embodied carbon of additional drywall for an HRV installation would have significantly increased without corresponding energy savings in the mild climate zone.
What This Means for Homeowners and Builders
The study challenges the notion that existing buildings should always be preserved for environmental reasons. While every situation is unique, the data suggests that replacing an inefficient single-family home with a well-designed, low-embodied-carbon Passive House can be the better climate choice, especially in colder climates and over longer time horizons. The researchers note that land use patterns are also significant. In cases where higher-density housing could replace a single-family house, the case for new construction becomes even stronger.
However, the study comes with important caveats. It is limited to single-family wood-frame houses, and different building types would likely produce different results. The analysis also does not consider scenarios where higher-density buildings replace single-family homes. Land use, transportation, and city-wide considerations are extremely significant factors beyond the carbon equation of individual buildings. The experience of seeing a project where when a house gets built backward lessons from a timber frame turnaround highlights how construction sequencing and design choices can dramatically affect outcomes, reinforcing that no single formula applies to every project.
For policymakers, the implications are clear. Building codes should address both operational and embodied carbon rather than focusing on energy efficiency alone. The province of British Columbia is already moving in this direction with greenhouse gas intensity targets that will be adopted by Victoria in 2025. Municipalities can reconsider policies that prioritize preserving existing single-family housing stock for environmental reasons when the data shows that new high-performance construction may be the better choice.
For builders and homeowners, the takeaway is that both renovation and new construction have a role to play in reducing carbon emissions from buildings. The greenest choice depends on the specific building, its location, the materials available, and the timeframe under consideration. What is clear is that the industry needs standardized tools for measuring embodied carbon, and that both operational and embodied emissions must be part of the conversation. The Passive House standard can be an effective part of the climate solution, but only when paired with responsible material choices and a holistic view of a building’s total carbon footprint over its lifecycle.