The (Carbon) Elephant in the Room

Carbon footprint as demonstrated by the number of carbon elephants emitted

There is an elephant in the room when it comes to our buildings, and it’s a carbon elephant… Every time we make or renovate a building, there is a carbon footprint as a result of the harvesting and manufacturing of the materials as well as the transportation involved. If we think this carbon footprint is negligible, we’re ignoring the elephant in the room!

Embodied carbon versus operational carbon
For many years, green building advocates maintained that the embodied carbon of building materials was not as important as reducing the operational energy use and carbon footprint. By this reasoning, it was justifiable to use materials with a high carbon footprint because they would eventually “pay back” that carbon “investment” with reduced energy use over time.

It’s not a trade-off
However, it is possible to make buildings with low-carbon building materials that match the energy efficiency performance of buildings that use high-carbon solutions. It’s a win-win solution… but it takes some adjustments to our way of thinking about buildings.

The carbon elephant
A comparison of the carbon footprint of a few different types of building shows that there can be a huge difference based on just a few material selections.

 

Carbon emissions of various construction types (from Making Better Buildings)

 

This chart shows the same 1,000 square foot house (based on the model house in the book Making Better Buildings). The two conventional approaches differ only on the choice of exterior cladding, one brick and the other vinyl siding. They have a carbon footprint many times larger than a best practice home made from low-carbon materials. But surprisingly, the straw bale home using lime-cement plaster actually has a carbon footprint slightly higher than a conventional home with vinyl siding. The same bale home plastered with clay has a dramatically lower carbon footprint.

Carbon sequestration
The carbon footprint numbers shown in the chart assign a carbon footprint to the cellulose materials (wood, straw, cellulose insulation), but don’t take into account the carbon sequestration effect of bundling a lot of carbon-based material into a building for a long period of time. There are conflicting notions of how to account for this, but at the very least there seems to be agreement that the sequestration completely offsets the carbon footprint. There is some reasonable argument to be made that these materials can actually have the effect of negating some of the building’s carbon footprint… that is, create a negative amount on the building’s leger. Things look different when this is taken into account!

Carbon emission footprint with sequestration of cellulose material at 25% of material weight

Carbon emission footprint with sequestration of cellulose material at 25% of material weight

By eliminating the carbon footprint for cellulosic materials and giving a sequestration factor of 25% of the total material weight, the carbon footprint can actually be put into the negative. However, those striving for carbon neutrality must remember that sequestration relies on the growth of new bio-mass to absorb CO2… we need to plant trees to replace those we’ve used in order to ensure these figures.

Carbon footprint as demonstrated by the number of carbon elephants emitted

Carbon footprint as demonstrated by the number of carbon elephants emitted

Different approaches not equal
The world needs carbon reductions immediately. Ensuring high carbon output today with the hope of a long-term reduction is a questionable strategy; it’s better to bank on getting our carbon footprint reduced now, especially if we can do so without sacrificing future reductions in the form of energy efficiency. When we start building very efficient buildings, the carbon footprint of the materials can start to equal many years of operating energy.

Carbon footprint by embodied carbon, 1 year and 10 year operational carbon for three climate zones

Carbon footprint of a foam-home, a high performance low carbon home and an older home, by embodied carbon, 1 year and 10 year operational carbon for three climate zones

This graph shows the embodied carbon of a high performance building using foam insulation, a best-practice low-carbon building and a largely un-insulated low-carbon building in different climate zones. Note that with best practice, there can be almost 10 years of operating energy before the building has the carbon footprint of a foam-based high performance house. And that’s without taking any sequestration into account! Obviously, we want to avoid the huge footprint of poorly insulated buildings, but ideally we want to do so in a low-carbon way. If we can build a low carbon home and use it for 7-8 years before we have the carbon footprint of a foam home, this is the option we should pursue!

No small effect
There were over 220,000 new homes built in Canada in 2014. Using conventional materials, these homes account for over 3 million metric tonnes of CO2 output. Using best low-carbon building practices can eliminate that altogether, and could even contribute 0.5 million tonnes of sequestration… more than 3.5 million metric tonnes of CO2 reduction!

Canada’s commitments under the Copenhagen Accord call for us to reduce about 127 megatons of CO2 given 2013 output figures. A move to building carbon-conscious homes could get us almost 3 percent of that target, in one industry, with little need for re-tooling or re-training of trades AND using materials that are harvested and produced in Canada. As a bonus, such homes are not necessarily any more expensive or difficult to build.

Kind of puts a positive spin on things, no?

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