Two reports on more than 500 newly constructed homes in Canada confirm earlier studies showing that the selection of building materials dramatically affects the climate impact of residential construction, outweighing the importance of energy efficiency for decades after the house is built.

Results suggest that the choices builders and designers make about foundations, insulation, cladding, and other materials are far more important in lowering carbon emissions in the near term than the energy it will take to operate the houses. With scientists warning that sharp reductions in carbon emissions are essential in the coming decades, the research shows thatchoosing low-carbon materialscan have a bigger impact on global warming and climate change than building净为零的能源房。

研究人员研究了不列颠哥伦比亚省和多伦多地区的537栋房屋，并分析了该房屋。体现碳用来构建它们的材料。住房单元代表了各种样式和大小以及不同水平的能源效率。

Chris Magwood of Builders for Climate Action, which helped carry out the research, said that the importance of embodied carbon has come into sharper focus in the last several years, but emissions related to the operation of the building are still significant.

“整个消息我一直想带,especially to municipalities who are thinking about this, is please don’t think of these two things as isolated metrics,” he said in a telephone call. “You can’t pursue one without thinking of the other, and vice versa. It isn’t always about energy efficiency and it isn’t always about materials. It’s always kind of a play between the two.”

Before anyone moves into a new house, the building is responsible for an average of between 30 and 40 tons of greenhouse gas emissions. Material carbon emissions for an all-electric new house will be greater than the operational emissions for about 60 years; material-related emissions for a new house heated with gas will outweigh its operational emissions for about 15 years, Magwood said.

The results mirror earlier work, including a 2021 report for Natural Resources Canada, that found embodied carbon in building materials (what is called Material Carbon Emissions or MCE in the reports) can outweigh operational carbon emissions (OCE) for as much as a century-and-a-half where the electrical grid is relatively clean. The findings are getting more attention as UN’s Intergovernmental Panel on Climate Change and others continue to warn of the looming climate crisis.

“The very short amount of time available to meet Canada’s emission reduction targets of 40‑45% below 2005 levels by2030requires us to consider all of the emission impacts from the housing sector and focus effort on those sources of emissions that have the greatest immediate impact on our remaining carbon budget,” the introduction to one of the two reports says.

The smaller of the two studies, which analyzed 34 homes inNelsonand nearby Castlegar, British Columbia, was prompted by concerns that some materials used to build high-performance houses might be responsible for high levels of greenhouse gas emissions. Houses insulated with lots of spray polyurethane foam, for example, used less energy for heating and cooling, but come with a high carbon price tag.

研究人员发现，节能的结构不一定是碳含量的预测指标。Magwood说：“有高效率的建筑物具有低碳的碳和低效率的建筑物，具有高体现的碳。”“更多的是，您选择提高建筑物效率的材料是差异，而不仅仅是更节能。您可以在不推动具体碳的情况下具有这些水平的性能，但是必须使用合适的材料套件来完成。”

是也没有必然的直接联系en cost and carbon content. Choosing materials with a low-global-warming impact doesn’t necessarily cost builders or homeowners any more money. Materials with the greatest carbon impact are standard blends of concrete, cladding, and insulation. Low-carbon substitutions are available.

How the work was carried out

多伦多的研究人员称他们的研究尴尬, for Emissions of Materials Benchmark Assessment for Residential Construction. They examined as-built residential housing units—single detached, semi-detached, and townhouses—that are representative of 16,400 new homes built in the region annually. The research covered carbon emissions in the extraction and transportation of raw materials and processing them into building materials, called “cradle to gate” accounting.

使用标准化的环境产品声明（EPD）和称为碳估计工具光束，研究人员研究了来自八名开发人员的59个样本房屋计划，以计算503个住房单元的总材料排放。

Not everything that went into the new homes was counted. Researchers excluded mechanical systems, electrical and plumbing, as well as paint, millwork, and fixtures and appliances. In some cases, researchers didn’t have EPDs for the products. In others, there were no meaningful substitutions for the materials. In the case of paints and surface finishes, the materials didn’t meet a 25-year minimum lifespan. In all, excluded materials could represent just as much carbon as the materials that were counted.

温室气体排放表示为每单位材料（例如立方米或平方米）的二氧化碳等效二氧化碳（kg二氧化碳）。横梁计算器在某些农业或森林产品中说明了碳存储，但由于使用当前会计方法，它因“重要且尚未解决的问题”，因此不信用木材（如木材）等维珍森林产品的碳存储。其中包括在伐木操作过程中从土壤中释放的碳，从根和磨坊浪费中释放的碳以及切碎的碳存储。

To sort out the results, researchers not only looked at total carbon emissions (MCE) but also at the Material Carbon Intensity (MCI), which is total carbon emissions divided by the floor area of the building. This allowed researchers to compare the carbon content of houses of different sizes.

研究人员还提出了另一种指标，碳使用强度，该指标结合了材料碳排放和运营碳排放。多伦多的报告说，两者的考虑对于理解新房屋产生的排放量更完整的情况至关重要。”

What researchers found

In the Toronto study, the lowest MCE was 9.5 tons of CO2 for a single home while the highest was 827.1 tons of CO2e. The 503 homes averaged 40 tons of CO2e each. When those numbers are extrapolated across the greater Toronto area, the total MCE for new homes is 840,000 tons, the equivalent emissions of more than 183,000 cars.

报告称，将近四分之三的材料碳排放量可以追溯到三件事：混凝土（33％），绝缘（26％）和覆层（13％）。但是，可用产品中有很多碳含量。例如，混凝土样品的全球变暖潜力范围从每立方米的124千克二氧化碳等效量到610 kgco2/m3的高度，具体取决于炉渣和粉煤灰的比例以及混合物中使用的水泥类型。

报告说：“虽然Mix Design提供了减少排放的机会，”新房屋可以通过最大程度地减少构造和/或替代处理的材料（例如处理过的材料）来使用较少的混凝土。木材基础。使用码头或销基础建造的房屋可以完全消除混凝土的使用。”

绝缘是第二大贡献者，但在这里，全球变暖潜力也涵盖了广泛的范围。迄今XPS的较新版本have a much lower global warming potential because of changes in the blowing agent used to manufacture it). Aerogel batts and closed-cell spray foam ranked second and third on the list after XPS, respectively. But some types of insulation have negative MCE values, including hemp fiber batts, cellulose, wood-fiber batts, hempcrete,wood-fiber board和稻草。稻草捆的碳纤维具有10倍。（在这项研究的房屋中，仅发现两种碳纤维隔热材料，即纤维素和木纤维板。）

Insulation poses special challenges for building designers. As the authors note, one strategy for lowering total material carbon emissions in new homes is to use less material. “But with increasing (and important) demands for improvements in home energy efficiency to reduce operational emissions, new homes will likely be using more insulation, not less. So as we push to improve energy performance we risk driving the significant MCE from insulation even higher.”

Insulation with lower emissions also may have lower R-values, so designers need to plan on more of it to get the same thermal performance in a house. That’s true for most types of conventional insulation—foam board, spray foam, mineral wool, and fiberglass. But for carbon-storing insulation, the more you use, the more carbon that can be stored.

覆层是研究院中使用的第三大碳密集型材料。砖是最糟糕的罪犯，其碳含量的近10倍，是乙烯基的10倍，除了研究中采样的房屋之一以外，所有碳含量都被使用。

At the moment, there aren’t any commercially available cladding options that store significant amounts of carbon. But researchers noted that one U.S. manufacturer, CalStar Brick makes a brick product with one-tenth the carbon content of typical bricks.

What material substitutions can do

Using the BEAM calculator, researchers also estimated the impact of substituting low-carbon materials for those with high embodied carbon. They studied two possible families of materials. The first is “best available materials,” those readily available in the Toronto market that meet current code requirements. That might include using cellulose batts instead of mineral wool or fiberglass batts, using engineered-wood cladding instead of brick, or switching to a low-carbon concrete mix.

A second option was to specify “best possible materials.” These include materials that are commercially available in other markets, and are code compliant elsewhere, but not necessarily possible substitutions now in the Toronto area. This step up might include materials such as straw-based insulation, interior walls made of压缩稻草板，一种由压缩再生饮料盒制成的干墙，以及油毡和软木地板。

当为碳强度最低的房屋指定“最佳可用”材料时，碳排放量下降了51％。当通过计算器运行“最佳”材料时，碳排放量下降了145％。

It’s interesting to note that the home in the Toronto study with the lowest MCI was a townhouse from a large developer, who researchers presumed “did not intend to achieve a low MCI score when it was designed or built,” meaning that this level of performance “could therefore be considered an easily achievable minimum target for conventional and cost-competitive buildings.”

If all new homes in the Toronto area matched that performance, it would reduce carbon emissions by as much as 465,000 tons, the report says, the same as removing about 100,000 cars from the road.

What about cost? In a competitive building environment already beset with supply chain issues, high inflation, and rising mortgage rates, can builders afford to make some of these changes in the interests of climate concerns? This is how the authors of the Toronto report addressed that issue:

“Though it was outside the scope of this report to comment accurately on the cost implications of material substitutions, correspondence with several regional concrete suppliers indicated that a low-carbon concrete mix substitution would not have any notable cost implications.”

Engineered wood siding costs between $7 and $12 per square foot, while brick cladding costs from $9 to $28 per square foot. Cellulose insulation was less expensive than the as-built choices in the study houses, although installation costs vary.

“On the whole,” the report says, “it is encouraging that the most impactful substitutions on emissions do not appear to have significant negative cost implications and could potentially cost less.”

Studies confirm earlier modeling

运营碳与材料碳排放的关系很复杂。在电网非常干净的地方（例如，在一个可再生能源构成发电的很大一部分的地区）可能需要一个多世纪的时间才能赶上材料选择的直接影响。但是，随着电网变得更脏，差距变窄。

萨斯喀彻温省北部就是这种情况，那里的网格基本上在煤炭和冬季的温度下运行真的很冷。在那里，解决能源效率的影响要大得多，因为气候很恶劣，发电机正在使用非常脏的燃料。运行碳的运营碳可能只有10或15年的时间等于建筑材料的前期碳罚款。

According to Magwood, the two studies confirm earlier work that was based solely on modeling. Critics could grouse that computer models can be made to produce whatever results researchers wanted. “What about real houses?,” they would ask.

“These are the real houses,” Magwood said, “and this is what it actually looks like on the ground today.”

These studies also are useful in establishing baseline carbon levels in new construction that could be used by municipal officials as a starting point for carbon reductions written into building codes. The average per-house carbon content in these recently studied homes fell in a fairly narrow range, somewhere between 150 and 190 kilograms of carbon equivalent per square meter, according to Magwood.

尼尔森的一所房屋以72公斤的二氧化碳/m2居住，而多伦多的许多房屋约为115或116，这表明建筑商即使没有专门尝试，也正在制造低碳建筑。

“They were just making the product, not even intending to make a low-carbon building,” he said, “and they’re already 30-40% under the average, so those kinds of numbers should be really achievable. It shouldn’t be a big lift to say 115 kg is a cap. The whole industry could move and make a pretty big reduction, and not even be challenging business as normal.”

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斯科特·吉布森是特约作者GBA and精美的房屋建筑杂志。