We Know How to Create Zero Carbon Buildings Right Now

(CREE’s LCT ONE, “the world’s first Lifecycle Tower,” pictured above, combines Passive House levels of performance with timber (CLT) construction. Image source: CREE.)

When it comes to the climate crisis, buildings are a big problem. According to the United Nations Environment Program (UNEP), buildings are responsible for 39% of energy-related emissions globally. What’s more, UNEP projects that between now and 2060 the world will double its current building stock. As Architecture 2030 points out, “That’s the equivalent of adding an entire New York City to the planet every 34 days for the next 40 years.”

But as is true for so many facets of the climate crisis, we have the solutions at hand. We know how to bring the carbon emissions of the building sector down to zero. We have the technology and materials. It’s cost-effective. We just need to make the transition.

Carbon emissions in buildings come from two sources: operational carbon (the ongoing emissions generated to heat, cool, and power the building, including both combustion onsite and fossil fuel-powered electricity generation offsite) and embodied carbon (the upfront emissions generated by the production of construction materials and components, the transportation of these materials to the construction site, and the energy used onsite to construct the building).

We need to eliminate both.

Passive House design and construction tackles the operational carbon problem. Derived from the German Passivhaus, or “Passive Building”, Passive House harnesses building science and an “envelope-first” approach to design to create buildings that require very little energy to operate—50–75% less than a typical building. These are structures that are carefully engineered to be leak-free, with continuously insulated walls, roofs, and foundations. When combined with building electrification, Passive House buildings routinely reduce operational carbon emissions by 90%. Add on the purchase of renewable energy (either generated onsite or purchased offsite) and your building can eliminate operational carbon emissions.

Two things are remarkable about Passive House. First, it brings lots of important “co-benefits” in addition to its revolutionary energy efficiency: superior indoor air quality and thermal comfort, heightened resilience and “passive survivability,” increased durability, less maintenance, and more.

Second, it is astonishingly cost-effective. In most US markets we see an upfront cost premium of around 5%, easily paid back by utility bill savings or lower vacancy rates. In some markets, particularly places with cold winters like Pennsylvania, Passive House appears to be no more expensive, and may perhaps be even cheaper, than conventional construction. The extra investment in the Passive House building envelope is offset or “paid for” by dramatically down-sized mechanical equipment. As the chart of 268 proposed construction projects shows below, cost data from the Pennsylvania Housing Finance Agency (which grants preferential scoring to Passive House projects proposals for its Low Income Housing Tax Credits) suggests that Passive House affordable housing projects are 1% cheaper than conventional projects.

Because Passive House has the power to deliver zero operational carbon buildings at little or no added cost, policymakers around the world have incorporated Passive House as a centerpiece of their emissions reduction policies for buildings. Leading jurisdictions in North America include the City of Vancouver, BC, the Province of British Columbia, the national government of Canada, as well as New York City, New York State, Pennsylvania, and Massachusetts.

But what about the upfront, embodied carbon emissions from these Passive House, zero operational carbon buildings? Groups like the Embodied Carbon Network, Architecture 2030, and the International Living Future Institute are at the forefront of examining the embodied carbon of buildings and charting pathways to turn buildings into carbon sinks. Global construction giant Skanska is spearheading the development of a new opensource and free software tool, called EC3, to empower designers to specify low- and negative-embodied carbon materials.

Recently completed graduate work by Chris Magwood, Executive Director of the Endeavour Centre Sustainable Building School, finds that high performance building projects (e.g. Passive House) amplify the impact of embodied carbon decisions, either positive or negative. If high performance building projects use high-embodied carbon materials, then the upfront belch of carbon emissions from those buildings is bigger than that of conventional buildings and negates any benefit from operational carbon reductions.

However, when high performance buildings use low-embodied carbon and carbon-sequestering buildings materials, they can become carbon sinks and perform significantly better on embodied carbon than conventional buildings. The primary reason for this amplification effect is that high performance buildings use lots of insulation, and the embodied carbon of insulation can either be very bad or very good. An example of the former is XPS foam insulation, which is made with HFCs that have a very high global warming potential, hundreds of times more harmful to the atmosphere than carbon dioxide. An example of the latter is the carbon sequestration of natural cellulose insulation.

Magwood finds that a simple prescription of readily-available, low- or negative-embodied carbon design moves can drive the upfront carbon emissions of buildings down to (or even below) zero. These include:

  • Use of cellulose insulation in walls and attics.

  • Use of wood fiberboard exterior insulation.

  • Specification of concrete mixes with high percentages of supplementary cementitious materials (SCM).

None of this is rocket science. None of it requires new technology. None of it is expensive, or needn’t be. While we face a big challenge in shifting how the construction industry designs and builds buildings, we know how to create zero carbon buildings right now.

To paraphrase Greta, how dare we not?

Author: Zachary Semke