Choosing the Right Building Materials for a Low-Carbon Future

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 Maywood, 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 from 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 on-going 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A carbon storing building would utilize concrete where much of the Portland cement has been replaced by fly ash or other substitute materials.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. Maywood’s hunch is that there will be even bigger climate-impact opportunities with remodels.

Retrofitting Homes to Become All-Electric

Weaning homes off natural gas and other fossil fuels would significantly reduce carbon emissions. Scientists report that fossil fuels consumed in our buildings across the globe account for 28 percent of climate change, while natural gas leaks upstream from our appliances account for another 25 percent of global climate change. Fuel burning appliances are entrenched in our homes, making the shift to electric appliances a challenge, even to homeowners so inclined.

The City of Santa Barbara is finalizing an all-electric code for new construction, joining more than 40 other cities and counties in California. Most likely, Santa Barbara and Ventura counties will consider similar code changes soon, but what can be done about existing structures, nearly all of which are not all-electric?

Redwood Energy, a California energy consulting firm, has published, within the last few weeks, a peer-reviewed report laying out detailed information on how the conversion of an existing home can be simple, relatively inexpensive and without building modification, not even upgrading the electrical service. This report, A Pocket Guide to All-Electric Retrofits of Single-Family Homes, lays out two paths toward electrification.

One path is an appliance-by-appliance conversion. This incremental approach, where an electric equivalent model replaces a gas-burning appliance may have no cost difference, especially if the old appliance needs replacing anyway. If a new 240-volt circuit is needed, there would be an added cost of between $85 and $600.

The second path is where all appliances are replaced at one time. This can cost between $3000 and $20,000 or more, depending on whether building upgrades are included like adding insulation or new high-performance windows.

Most existing homes have a 100-amp service panel; a few older ones may have only a 60-amp panel. The report lays out how a 3000 square foot home can be completely electrified without upgrading a 100-amp service. Choosing efficient appliances such as heat-pumps that are three to five times more efficient makes this possible. Switching to water heating or space heating/cooling heat-pumps usually means running new 240-volt lines but appearing on the market for the first time this past year are 120-volt models than can plug into any wall outlet.

Another strategy is using circuit-sharing plugs where one 240-volt outlet can handle, for example, an electric dryer and a heat-pump water heater, or a magnetic induction stove and an electric vehicle charger. These circuit-sharing plugs range between $200-$500 but save money by requiring fewer new circuits and often no panel upgrade.

Redwood Energy’s report is full of useful information on design, assessing existing electric panels, rebates and tax credits, plus utility and community choice energy incentives (coming to Santa Barbara this October). It contains an extensive catalog of devices that covers everything from heating and cooling to cooking, water heating, whole-house ventilation, countertop ovens, kitchen hoods, power-sharing plugs, and even slow cookers.