Embodied Carbon: Reduce Your Home’s Hidden Carbon Footprint
CategoriesSustainable News Zero Energy Homes

Embodied Carbon: Reduce Your Home’s Hidden Carbon Footprint

Operational carbon is usually what we think of when energy costs are discussed. That is, carbon emissions that come from the energy used to power our homes, cars, etc. over their lifetime. Your home’s energy efficiency comes into play here. Generally, operational carbon emissions can be modeled and predicted, so you can compare one appliance or building product against another. Often, a label will show how much energy a certain appliance is likely to draw over a lifetime of operation, or how much a well insulated house will reduce your energy needs annually. But embodied carbon takes this modeling to a whole ’nother level.

Embodied carbon is the carbon footprint of a product, process, or service starting with the extraction of raw materials through the manufacturing process to market (cradle to gate) and then beyond to delivery and installation (cradle to site). Operational carbon is often considered separately, but adding the carbon embodied in a product’s end-of-life disposal (cradle to grave) or reuse or recycling (cradle-to-cradle) gives a complete lifecycle analysis. In other words, embodied carbon represents the total amount of greenhouse gases (including CO2) emitted during extraction, transportation, manufacture, delivery and deployment, and then end-of-life. Looking at both the embodied carbon and the operational carbon give you the true “carbon cost” of your product or project.

Let’s picture a new countertop for your kitchen. The embodied carbon of that countertop that you will enjoy in your home comprises the energy that goes into mining the stone, transporting the raw material from the mine to a facility for processing, its processing and preparation (cutting, strengthening, and polishing), transporting to a wholesaler, and then to your home where we include the energy emissions of cutting to size and setting it up in your kitchen. And finally its end-of-life, which hopefully includes reuse or recycling wherever possible.

Hardware store assortment, shelf with stainless steel mortise sinks, nobody. Building materials and tools choice in diy shop, rows of products on racks

Embodied carbon hides in your home

For homes, the biggest sources of embodied carbon are typically in materials. Many common materials used in construction, such as concrete, stone, steel, and lumber, tend to be high in embodied carbon either due to energy-intensive extraction or manufacturing processes. Even products made from rapidly renewable materials, or by a manufacturer that uses renewable energy, may waste a lot of water, or raw or finished materials. Or the product must travel overseas, or lasts only a short time before it heads for the landfill and must be replaced.

An exception to looking for the lowest carbon equation would be if the building materials are used for carbon sequestration. For instance, natural renewable materials such as wood from sustainable forests, or wool, or bamboo will hold carbon safely within the walls and furnishings of your home, while the natural source is replenished and continues to grow and pull more carbon from the atmosphere.

To reduce the embodied carbon in your home, as the saying goes, you can’t manage what you don’t measure. The most accurate analysis of the embodied carbon in extraction, transportation, and manufacturing is going to come from the product manufacturer. Eco-conscious companies often use environmental product declarations (EPDs) and post the data on their websites. These look beyond carbon and account for multiple environmental impacts. Further, they provide a lifecycle assessment (LCA), and include both embodied carbon through end-of-life and operational carbon.

Experts can help

Many software tools exist to help conduct LCAs. One of the best free tools out there is the Embodied Carbon in Construction Calculator (EC3). This tool can technically be used by anyone, but it is most efficient if used between your architectural, engineering, and construction professionals along with a trained sustainability professional or firm. Increasingly, the emphasis shifts to embodied carbon as building codes call for increased energy efficiency, and more homes and utility grids are powered by renewable energy—thus significantly lowering the carbon footprint of operational carbon emissions.

By looking at these issues, weighing pros and cons, we can help reduce the embodied carbon and thereby the total lifecycle carbon in our homes. Particularly in new construction and all-electric homes, just a few adjustments in key areas—insulation, cladding, and concrete—can make strides toward meeting our collective climate change commitments and averting the worst of the climate change catastrophes to come.

 

The Author: Sustainability Consultant Arnaldo Perez-Negron is an environmentalist and social entrepreneur based in the Tampa Bay area.

 

Energy Efficient Homes Zero Carbon renovation.

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Low-Cost, High-Value Opportunities to Reduce Embodied Carbon in Buildings
CategoriesSustainable News Zero Energy Homes

Low-Cost, High-Value Opportunities to Reduce Embodied Carbon in Buildings

Buildings account for at least 39% of energy-related global carbon emissions on an annual basis. At least one-quarter of these emissions result from embodied carbon, or the carbon emissions associated with building materials and construction. The solutions for addressing embodied carbon in buildings have not been widely studied in the United States, leaving a significant knowledge gap for engineers, architects, contractors, policymakers, and building owners. Further, there is little information about the cost-effectiveness of reducing embodied carbon in buildings.

RMI’s new report, Reducing Embodied Carbon in Buildings: Low-Cost, High-Value Opportunities, helps fill this knowledge gap. The report demonstrates low- or no-cost options to reduce embodied carbon in buildings and provides design and construction strategies that can help limit a project’s embodied carbon. The case studies showcased in the report show an embodied carbon savings potential of 19% to 46% at cost premiums of less than 1%. Current practice indicates that we can achieve these reductions by specifying and substituting material alternatives with lower embodied carbon during the design and specification process. Far greater reductions are possible through a whole-building design approach.

This report was developed to help building owners, designers, contractors, and policymakers understand the low-cost and no-cost solutions for reducing embodied carbon in buildings. To accomplish that, we studied three building types and considered design strategies that can reduce embodied carbon at any stage of a project’s design and construction phases. The report quantifies the construction cost difference associated with low-embodied-carbon solutions and points to next-generation solutions that could drive even greater reductions.

 

Top categories of building materials for reducing embodied carbon.

 

Critical Materials Driving Embodied Carbon in US Buildings

In order to tackle embodied carbon in buildings, we first need to understand the carbon impact of the industries driving embodied carbon emissions. A building’s structure and substructure typically constitute the largest source of its up-front embodied carbon, up to 80% depending on building type. However, because of the relatively rapid renovation cycle of building interiors associated with tenancy and turnover, the total embodied carbon associated with interiors can account for a similar amount of emissions over the lifetime of a building. Our report focuses primarily on structural materials, metals (including steel and aluminum), cement, and timber. Each of these materials has a different embodied carbon content but is critical to our consideration of structural systems in this context.

 

Proven Solutions and Strategies to Reduce Embodied Carbon

Today, there are many solutions that can be leveraged to limit embodied carbon in new buildings. The totality of low-embodied-carbon solutions includes a long list of offerings that span a wide range of complexity.

Most simply, low-embodied-carbon solutions for buildings can be broken down into three main categories: whole-building design, one-for-one material substitution, and specification. In general, whole-building design solutions can drive the greatest embodied carbon savings. However, material substitution and specification can also result in substantial embodied carbon savings, especially when these solutions target carbon-intensive materials such as concrete and steel. Furthermore, these categories are not mutually exclusive — they can be combined or performed in parallel to drive deeper embodied carbon savings.

The following graphic demonstrates embodied carbon best practices that can be implemented throughout the building design and construction process.

Case Studies in the Economics of Low-Embodied-Carbon Buildings

One core objective of the report is to answer the question: How much can we reduce embodied carbon in new buildings at no additional cost?

In short, this study shows that embodied carbon can be reduced by 19% to 46% in mid-rise commercial office, multifamily, and tilt-up-style buildings by leveraging low- and no-cost measures. Together, these measures increased overall project costs by less than 1%, which is within the margin of error for most construction project budgets.

 

Skanska, one of the world’s leading sustainable construction firms, provided cost data from three actual projects in the Pacific Northwest and conducted an analysis under the guidance of RMI to generate the results of this study.

These case studies lead us to a few powerful observations. Even though the strategies employed do not include comprehensive, whole-building design strategies, they still yielded reductions of up to 46% in up-front embodied carbon through specification and material substitution measures. Given that these conclusions are based on three case studies in the Pacific Northwest, we can note them as strong anecdotal evidence, rather than broadly applicable conclusions.

Given the fact that we were not able to redesign building structural systems, we were unable to draw deep conclusions about the cost, carbon, and material impacts of whole-building design solutions, such as substituting more structural steel and concrete with wood. Given this scope, our key findings are:

  1. Optimizing the ready-mix concrete design can lead to significant embodied carbon reductions (14% to 33%) at no cost, or with a possible cost reduction in some cases.
  2. Rebar contributed up to 10% of total project embodied carbon in two case study buildings, but rebar’s up-front embodied carbon can be cut in half with minimal cost impact to the overall projects. These results may vary by location, as rebar with high recycled material content may not be available at a low cost premium in other regions.
  3. Insulation material selection can be a significant factor in project-level embodied carbon, with insulation making up approximately 20% of one building’s baseline embodied carbon content. Insulation products utilizing hydrofluoroolefin (HFO) or other foaming agents with low global warming potential can reduce embodied carbon impacts significantly, and several emerging plant-based products have the potential to store more carbon than is emitted in their production.
  4. Glazing remains a critical challenge for reducing embodied carbon, between the significant amount of heat required for glass production and the high-embodied-carbon materials often used for framing. Products available today can cut embodied carbon in glazing by approximately 25%, but at a 10% cost premium.
  5. For some finish materials such as flooring, carpet tiles, ceiling tiles, and paint, embodied carbon reductions of more than 50% are possible at no up-front cost premium. In some locales, carbon-sequestering materials may even be available.

 

Read the Report to Learn More

The Reducing Embodied Carbon in Buildings report includes detailed information about each of the three building case studies, sections exploring related topics such as tenant fit-outs and building reuse, and further analysis of our key conclusions. Download the report to learn more about opportunities for reducing embodied carbon in buildings, and why embodied carbon needs to be addressed now to drive the most impact.

 

Matt Jungclaus is Manager of Carbon Free Buildings at the Rocky Mountain Institute

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Tackling Embodied Carbon in Retrofits
CategoriesSustainable News Zero Energy Homes

Tackling Embodied Carbon in Retrofits

A firm specializing in remodeling rethinks its approach to attic and roof insulation to lower embodied carbon.

By Rachel White

In 2018, the Intergovernmental Panel on Climate Change (IPCC) put the world on notice: To avert catastrophic and irreversible climate change, we will have to hold global warming to 1.5°C above pre-industrial levels. And to keep warming at this level, we must cut global emissions roughly in half by 2030 and get to zero by 2050.

Building Sector Contributions to Global Warming

The building sector is a huge part of the problem, accounting for roughly 40% of global annual emissions. And while our industry has made progress, we haven’t done nearly enough.

Along with the work of organizations such as the Carbon Leadership Forum and Architecture 2030, the IPCC report was a wake-up call about the time value of carbon. Larry Strain, a board member at the Carbon Leadership Forum, describes it this way: “Because emissions are cumulative and we have a limited amount of time to reduce them, carbon reductions now have more value than carbon reductions in the future [emphasis added].”

Carbon Reduction Strategies                                                          

Three strategies are critical to achieving meaningful near-term reductions in building sector emissions. First, we need to repurpose buildings rather than build new ones wherever possible. Second, we need to aggressively reduce the operating emissions of existing buildings. Third, we need to build with low embodied carbon materials and ideally with carbon-storing materials.

The first two strategies are firmly ensconced at Byggmeister. We don’t do new construction, we avoid additions, and we pursue operational emissions reductions whenever possible. However, until the last couple of years, we had not paid much attention to embodied carbon. We assumed that whatever carbon we emitted to renovate and retrofit homes would be balanced by operational savings over decades. But this assumption was flawed.

Embodied Carbon Emissions

So, we turned our attention to embodied emissions, focusing first on insulation. As remodeling contractors, we know that insulation is high leverage, especially because closed-cell spray foam—one of the highest embodied carbon insulation materials on the market—has long been a go-to insulation material for us. There are good reasons we have relied so heavily on closed-cell spray foam. It blocks air leaks in addition to reducing conductive heat loss; it’s vapor impermeable; and it’s highly versatile. But none of these is a good reason to maintain the status quo.

Deciding When to Use Foam

There are times when replacing spray foam with a carbon smarter material is a no-brainer. For example, installing cellulose in wood-framed walls is typically no more complex than insulating with spray foam, not to mention less expensive and less disruptive. And while the R-value of a cellulose-insulated wall is lower than the same wall insulated with closed-cell spray foam (unless the wall assembly is thickened), we believe this compromise is worth it. The reduced R-value has little impact on comfort and the carbon benefit more than makes up for it. Unlike spray foam, which emits a lot of carbon before, during, and immediately after installation ( especially true of closed-cell spray foam with high-embodied-carbon blowing agents), cellulose actually stores carbon.  

There are other cases, though, such as with rubble foundation walls, when we feel spray foam is the only viable choice, other than not insulating at all. While we have entertained this possibility, we aren’t willing to give up remediating dank, damp basements, although we have begun to think about these as emissions that should be offset with more aggressive carbon-storing measures elsewhere.

Roof Insulation Challenges

Much of the time, though, the choice to eliminate or retain spray foam isn’t clear-cut. We encounter many roofs and attics where existing conditions, code requirements, and broader project goals make it challenging but not impossible to avoid spray foam.

If the attic is unconditioned, then the easiest, most cost-effective strategy is to air seal any penetrations along the attic floor and then re-insulate (in most cases, we would first remove existing insulation).

But this only works if there’s no mechanical equipment (and ideally no storage). If the attic is used for anything other than insulation, best practice is to bring the attic space indoors, either by insulating the underside of the roof sheathing with spray foam or by removing the roofing, insulating the topside of the roof sheathing with rigid foam and then re-roofing.

If the roof needs to be replaced, “outsulation” might initially seem viable. But I can count on one hand the times we have actually done it. More often than not, it’s doomed by cost or adverse architectural consequences. This is why spray foam has long been our go-to approach for unconditioned attics with HVAC equipment.

New Approaches for Lower Carbon

At least it was until we realized just how carbon-intensive it is. We came to this realization by comparing the embodied emissions of spray foam against four alternatives. We based these comparisons on a simple gable-roof form. The four alternatives we looked at were: 

* A low-foam approach of building down the rafter bays, insulating with closed-cell foam for condensation control, followed by cellulose behind a smart membrane.

* A no-foam approach where the air and thermal boundary remains at the attic floor. We install the air handler in a conditioned “head house” and bury the ductwork in cellulose. 

* A common outsulation approach with cellulose in the rafter bays plus exterior polyisocyanurate board foam.

* A newer, no-foam outsulation approach with cellulose in the rafter bays plus exterior wood fiber board.                                                                                                                                                                                          All of these approaches, including exterior polyisocyanurate, are either carbon neutral or carbon storing from the outset. Only spray foam starts off in carbon debt.

This chart shows the embodied carbon of several options for insulating the attic floor or the roof. Chart courtesy Byggmeister.

What we call the “low foam” approach includes 3 inches of closed-cell spray foam on the underside of the roof deck plus 8 inches of cellulose and a membrane to control moisture. Illustration courtesy Byggmeister.

And this debt is not small. Our modeling suggests this particular measure would take 14 years of operational carbon savings to break even. Even if our model isn’t exact, it’s close enough to know that spray foam should not be our default approach if there are viable, lower emitting alternatives.

In Two Carbon Smart Ideas for the Attic, we walk through the no-foam, head house approach in detail. We also describe our efforts to develop a carbon-smart approach to another common attic/roof condition: poorly insulated, finished slopes. When such slopes are topped by a “micro attic,” we are experimenting with dense-packing the slopes, installing loose-fill cellulose along the floor of the micro-attic, and adding a ridge vent.

We Must Take Risks

Both of these approaches seemed impractical when we first took them on. Both present some level of risk. Because of code constraints, the second one may not be broadly replicable even if we can demonstrate that the risk is manageable. But if we are going to cut global carbon emissions in half by 2030 and get to zero by 2050, we’ll have to take some risks and pursue approaches that aren’t (yet) standard practice. By sharing our story, we hope to inspire more of our colleagues to join in this effort.

Rachel White is the CEO of Byggmeister, a design-build remodeling firm in Newton, Mass. This article was first published in Green Building Advisor.

 

 

 

 

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