Boulder, the largest city in Colorado to ban gas in new construction, is also pioneering climate-friendly building practices beyond energy use.
Until now, Boulder has focused on reducing the climate impact of its buildings through energy-saving solutions like heat pumps and better insulation. Starting in December, the city’s new energy code will encourage builders to improve the sustainability of the building materials themselves.
Traditional building materials, like concrete and steel, have a hefty carbon pollution footprint. The global warming emissions released while extracting, producing and transporting these materials are greater than those for alternatives like cross-laminated timber and recycled materials. By pushing climate-friendlier options, Boulder hopes to reduce its overall carbon footprint. Buildings are Boulder’s largest source of greenhouse gas emissions, producing nearly two-thirds of city emissions.
“The operational emissions we save in a building are dwarfed by all the embodied carbon in that building,” said Carolyn Elam, a sustainability senior manager for the city.
The city says its incentives for “embodied carbon” — emissions released from processes like mining iron ore for steel beams and burning coal or gas to heat limestone and clay for traditional cement — are the first in Colorado and among the first in the nation. They represent a new approach in the fight against climate change.
Because of the novelty of embodied carbon in its energy code, city staff included it as incentives rather than regulation.
When building a new home or commercial building, Boulder homeowners and developers need to accumulate conservation “points” to meet the code. This is the first time low-embodied carbon can be used to get points. So, in addition to steps like installing a ground source heat pump or battery storage for solar, residents and developers now have an incentive to build with lower-embodied carbon materials, like cellulose insulation or cross-laminated timber.
“We saw it as an opportunity to use a little bit of a carrot approach,” Elam said. “So we can think about in the future what we might regulate through our broader building codes.”
Lauren Folkerts is an architect and the Boulder City Councilmember who led the push to include embodied carbon in the code. Folkerts emphasized that the problem with embodied carbon is that all those emissions are in the atmosphere by the time the building is complete. So even if the new building is energy-efficient and will contribute fewer total emissions in the future, it may not be enough to offset the extra emissions from building materials for decades.
“If we are increasing the amount of emissions right now, today, we are increasing the risk we are facing due to the climate catastrophe,” Folkerts told Boulder Reporting Lab.
The code also aims to incentivize reusing materials at the end of a building’s life rather than throwing them away, which contributes to climate change. It encourages dismantling old buildings for salvageable parts and designing new buildings so they can be easily disassembled and their materials reused.
According to Elam of the city, the code also tries to cut down on embodied carbon emissions by making requirements less stringent for deep renovations or gutting a building. The goal is to encourage keeping existing buildings and preserving the carbon already used in them, as opposed to demolishing and starting over.
But even in new builds, the answer isn’t always simple. Climate-friendly building materials are sometimes only available from distant locations, meaning emissions from transport can override their climate benefits. Elam said another goal with these new incentives is to drive market shifts by creating more demand for them. “Then materials could be more readily available,” she said.
Some readily available building materials have hidden carbon costs. Folkerts cited spray foam insulation as an example of a problematic material. Because of its effectiveness per square inch, spray foam is a common choice for contractors and home builders in tight spaces. However, spray foam soaks into surrounding building materials, making those pieces unsalvageable when a building is taken apart. This increases emissions because those materials can’t be reused.
“When something has been spray-foamed on the inside,” Folkerts explained, “it turns that wood from being a recyclable material to being trash.”
There are challenges to encouraging people not to use such materials. Folkerts cited a state requirement in the code for insulation in remodels that mandates a level of insulation nearly guaranteeing homeowners will use spray foam when remodeling older homes. The energy savings will often never be enough to outweigh the carbon footprint of the spray foam and the harm it does to the recyclability of nearby materials, Folkerts said.
“The buyback on energy savings,” she said, “is never.”
City staff and councilmembers will return to these conundrums soon, as conversations around adopting an updated building code, different from the energy code, are expected to begin in the first quarter of next year.
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