Many have advocated for tight houses with low-energy needs and highly efficient mechanical systems as one of the best ways to address climate change. California now requires all new houses to be zero-net-energy, although natural gas is still allowed. A new study by Chris Magwood, director of the Endeavour Sustainable Building School in Ontario, Canada, questions this singular focus on cutting building energy use. His research concludes that curbing the emissions resulting for the harvesting, manufacture, and transport of building materials — what he calls a building’s up-front embodied carbon emissions (UEC) — is significantly more important than the contribution from running a building on clean, renewable energy.
Zero-net-energy makes a big impact on carbon emissions, but most of that impact is in future years as a result of ongoing zero-energy consumption in the building’s operation. On the other hand, if UEC is zero or even provides net carbon storage, the impact on climate is immediate and powerful. Emissions that are avoided today do more to slow climate change than emissions that are averted in the future.
What materials make the difference between a high UEC structure and one that stores carbon? A high-carbon house would use such common construction materials as standard concrete, extruded polystyrene insulation, brick cladding, steel-frame vinyl windows, tile and carpet flooring, and concrete or clay tile roofing.
A carbon-storing building would utilize concrete where much of the Portland cement has been replaced by fly ash or other substitute materials. It would be insulated with cellulose and wood fiberboard. Sustainably grown wood would be used for the framing, for wood flooring, for wall paneling, and for wood windows. Linoleum might also be on the floors. Sun-baked Mexican clay tiles (low-embodied energy) would be a good roofing choice for our high-fire area. The study recommends plant-based building materials such as straw panels, hemp fiber board, and rice-straw medium-density fiberboard, because they prevent the release of stored carbon for the life of the building.
Because the report only focused on materials that are available, code compliant, and affordable, architects and builders can make major carbon reductions with only minor adjustments to what we already do. The optimum, obviously, is to create carbon-storing buildings that also run on renewable energy.
The conclusions in this report are a major revelation to the building industry. The analysis relates only to new construction, but the same team is undertaking a new study covering retrofits. Magwood’s hunch is that there will be even bigger climate-impact opportunities with remodels.