By Tory Coffin
Why does carbon-conscious building matter?
Buildings and construction account for 39% of carbon emissions globally. This is composed of both the “embodied carbon” which goes into the construction and the ongoing operational energy needed to run it.
“Net zero emissions” refers to eliminating human-caused carbon emissions as much as possible and “balancing” remaining emissions through carbon sequestration and/or carbon-free credits. Ultimately, the goal is to arrive at carbon neutrality or “zero carbon.” Some cities even mandate zero and low-emission building. However, combatting the climate crisis will require going beyond carbon neutrality to more innovatively remove carbon from the atmosphere.
Carbon positive building presents the perfect opportunity to push building standards. For homeowners, it offers a host of benefits — financial, environmental and even health-related.
So, what exactly are carbon positive homes?
Carbon positive homes take the concept of carbon-neutral design one step further by producing more energy on-site than the building requires to operate — sending energy back to the grid and setting a new standard of sustainable living. We achieve carbon positive homes by building with low embodied carbon materials and creating an energy surplus under operation.
Tackling Embodied Carbon
Carbon positive design begins with the use of sustainable building materials, which reduce “embodied carbon” — all greenhouse gas emissions that result from producing, transporting, and installing the building materials. Many materials actually sequester carbon — removing it from the atmosphere as it is created and effectively storing it for the life of the building. Choosing bamboo, cork, straw, hempcrete, cellulose fiber, and wool insulation, and even timber products sourced from sustainably managed forests are all good choices. You can find more by using the Building Transparency’s Embodied Carbon in Construction Calculator which allows you to assess the embodied carbon associated with different building materials. Offsite construction whether prefab homes or pre-building walls or trusses is also a great option to reduce construction waste.
With about half of a home’s energy consumption used for heating and air conditioning, design features that maximize natural heating and cooling or “passive solar design” go a long way. There are a number of energy-saving building features to consider adding to a new project or your current home, including:
- Building orientation — The orientation of a building should maximize solar radiation by facing the sun’s true positioning. Several windows should be located on the southern side of a building and fewer on the northern side where the sun rises in the summer. The floor plan should also be oriented towards the sun. Consideration should also be given to landscaping — deciduous tree(s) located on the south side of a home lose their leaves in winter, allowing light to enter, whereas evergreen tree(s) on the northside offer shade in the summer.
- Awnings and overhangs — reduce air conditioning costs by creating shade along a building’s south-facing periphery. The generated energy savings are most notable during summer months as shading minimizes heat transfer through windows, cutting cooling costs around $200 annually. Adding external shading is a cheap retrofit project to make your home more eco-friendly.
- Airtight building envelope — prevents warm or cold air from escaping a building, maintaining indoor air temperature. It is a critical component of any carbon-positive structure because it lowers all energy costs by reducing the need for heating and air conditioning.
- Insulation — added to exterior walls, attics, and basements keep the indoor air temperature warm in winter and cool in summer. Homeowners can save 11 percent of their total energy costs by insulating their house, averaging $200 annually. Choose insulation that is sustainably-sourced.
- Energy-efficient windows — Look for windows with a high Energy Star rating, which meet efficiency criteria set by the EPA and consider several factors e.g. framing, UV resistance, and number of glass panes. Air can easily escape older windows, so updating or replacing your windows is a worthwhile investment.
- Green roofs & cool roofs — both provide natural cooling to your home. Cool roofs are a white or reflective color and include metal, tiles, or shingles which absorb less heat while reflecting sunlight. They can reduce indoor air temperature by as much as 50 degrees Fahrenheit in summer. Green roofs go one step further because they sequester carbon and purify the ambient air. They are a great option in urban areas where greenspace is limited.
- Garden walls — Similar to green roofs, garden walls (or vertical gardens) improve indoor air quality, reduce noise pollution, and cool indoor and outdoor temperatures — lowering summer energy expenses by 23 percent. Garden walls can be placed in a room with sun or shade depending on the vegetation type planted.
- LED lighting — is a high-efficiency lighting source that emits little heat. ENERGY STAR rated LED lights use 75 percent less energy and last 25 times longer than incandescent lights. If your home currently has incandescent lighting, switching to LED can cost between $100-200.
- Passive heat transfer — thermal mass which warms during the day and emits the warmth back at night is a “free” source of radiant energy. Think of a concrete or stone floor or wall that warms in the sun during the day. Another technique is earth tubes which cool and dehumidify air entering a building in summer, and warm air entering in the winter by bringing air from underground where the temperature is constant.
Energy expenses for heating, cooling, and lighting can be costly for homeowners. Annually, American families spend around $2,000 on energy bills. Energy efficiency not only lowers homeowners’ heating and cooling costs, but it also raises home values considerably.
Once your building project or home maximizes efficiency, you will want to use renewable energy to power your home — removing all carbon emissions from your operational energy usage. Your anticipated power usage can be calculated, and a carbon-free energy solution can be sized to meet those needs. There are various ways of addressing this for your home.
The cost of “going solar” has been going down each year. Installing solar panels or photovoltaics is safe and can qualify you for tax breaks and incentives. Homes with solar panels have been found to sell faster than less energy-efficient homes and at a higher price. Find what solar options will work for you.
In certain climates, wind energy is a viable option to power your home. On lots large enough, a small wind turbine can be installed. This means that you can generate power even overnight. Although installation is costly, government incentives can drastically reduce the cost.
Geothermal HVAC systems are regarded as sustainable and cost-effective space conditioning systems. They consist of underground piping that circulate water. Heat pumps exploit the differential in temperature between the surface and the constant temperatures underground to heat in winter and cool in summer.
Renewable energy credits offer a solution if on-site energy generation is not possible or scalable to the energy demands of your house. You can purchase these credits which represent renewable energy generation elsewhere to offset the energy which you are using on the grid or via other carbon-based sources.
The grid itself is going greener! Many cities have electricity which is either all renewable or allow a renewable option, California has committed to 100% clean energy on the grid by 2045.
Building Standards and Certifications
There are a number of building standards and certifications that recognize sustainable and resilient building design and have paved the way for carbon neutrality. While some standards focus entirely on a project’s operational energy usage, others are more rigorous by considering the energy inputs associated with construction and materials used.
Certified by the US Green Building Council, LEED Zero aims to encourage a holistic approach to building that achieves “net zero” goals — reducing greenhouse gas emissions and improving human health and wellbeing. To achieve the certification, a building must exhibit one or more of the following: net-zero carbon emissions, net-zero energy use, net-zero water use, or net-zero waste. A net-zero carbon emissions building, for example, must operate “with net-zero carbon emissions from energy consumption and occupant transportation to carbon emissions avoided or offset over a period of 12 months.” LEED Zero is unique in that it offers several different environmental performance metrics to earn the certification.
Unveiled in 2019, LEED Positive surpasses the LEED Zero criteria by requiring “net positive performance” in carbon, energy, and other LEED categories. Both new and existing buildings can be certified, although existing buildings must attain more stringent energy goals.
The International Living Future Institute’s Zero Carbon Certification is the “first worldwide Zero Carbon third-party certified standard.” It requires two components — 1) 100 percent of a project’s operational energy use must be offset by renewable energy (on- or off-site), and 2) 100 percent of the embodied carbon (relating to construction and building materials) must be disclosed and offset. To determine eligibility, a project’s energy use and production are assessed over a 12-month performance period, and a life cycle assessment of building materials is conducted to calculate total embodied carbon.
Powerhouse is a new building standard established by a coalition of companies that certifies buildings that produce more energy than they require throughout the lifetime of the structure — including the embodied energy of its materials, construction, and demolition. The most stringent of the standards mentioned, it requires a life cycle assessment of all building materials and assumes a 60-year operational phase. Powerhouse is in line with the 1.5 degrees Celsius warming threshold set by the Paris Climate Accord.
Carbon Positive Inspiration
Australian-based architectural practice Archiblox designed the first-ever carbon-positive prefab, a 1-3 bedroom home priced at $203,000 – $317,000 USD (before tax). Ideal for small urban spaces, the chic and modern home has a quick building timeframe — 5 weeks to build and one day to install. ArchiBlox claims that “over its expected lifetime of 105 years, the house will emit 1,016 fewer tonnes (1,120 tons) of CO2 equivalent.”
The ZEB Pilot House in Norway is another small carbon positive home that generates enough additional energy to power an electric vehicle throughout the year. It is a perfect model for sustainable living that demonstrates innovative and modern design.
Homeowner Bruce Sullivan built his zero energy home in Bend, Oregon which has saved him hundreds monthly in energy bills and generates surplus energy to charge his electric car. A number of energy-saving improvements can be performed yourself without having to invest much up-front.
Tah.Mah.Lah is an environmentally regenerative home that produces more energy than it consumes (even including transportation), restores native habitat, repurposes water, and reduces waste. This inspirational home is an early showcase for techniques to attain zero carbon emissions.
Ready to go carbon positive?
The Zero Energy Project is a nonprofit organization that works with homebuyers, builders, designers, and real estate professionals to build “zero net energy homes and near-zero energy homes.” It offers educational resources for buyers, sellers, and renovators of zero carbon and carbon positive homes. Subscribe to their free zero energy newsletter here.
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