It’s fine to create airtight, energy efficient houses, but a Nelson building consultant says there’s still something we’re forgetting: embodied carbon.
“That represents all the energy it takes to extract, transport, and manufacture the materials we build with,” Michèle Deluca of 3West Building Energy Consultants told Nelson council on Feb. 24.
The latest trends in energy efficient building include liberal use of such materials as concrete and foam insulation and the manufacture of these materials all have very high carbon footprints, Deluca said.
The carbon we use to heat our homes she refers to as operational carbon. That’s the carbon we try to reduce by making our homes airtight so we burn less fuel fuel.
That is the goal of the B.C. Energy Step Code, a provincial initiative that aims to have all new buildings at net-zero energy use by 2032, meaning the building must produce as much energy as it uses. The province is inviting municipalities to gradually increase their building requirements to meet this purpose, and Nelson is on board.
Deluca thinks the Step Code is a step in the right direction but it only addresses operational carbon, which starts to be emitted the day someone moves in.
“But on the very first day a building is built, all the embodied carbon is already implicated in the building materials.”
The manufacture of concrete amounts to between six and 10 per cent of worldwide CO2 emissions, she said, adding that foam products often used in construction can have four to five times the embodied carbon of a conventional wood frame home.
Deluca, a self-described “embodied carbon nerd,” envisions an energy efficient house made with alternate materials.
“This would be a house that has wood framing, insulation with cellulose, which is recycled shredded newsprint, the concrete foundation has low cement content, which can sub out some of the cement for fly ash. That reduces the cement content and does not affect the integrity of the concrete. It just takes a bit longer to dry.
“Then we put a heat pump in there. This is a building any builder could build today.”
Deluca said these strategies are affordable and have the advantage of improving indoor air quality because petroleum-based materials including foam can have negative health effects.
“By moving to low carbon materials we make a safer indoor environment,” she said.