Zero carbon housing

Zero-carbon housing and zero-energy housing are terms used interchangeably to define single family dwellings with a very high energy efficiency rating. Zero-energy housing requires a very low amount of energy to provide the daily needs and functions for the family occupying the home.

The term carbon footprint, at present, does not have a concrete and universal definition. Thomas Wiedmann proposed a well received and generally accepted definition that defines carbon footprint as a measure of the total amount of carbon dioxide emissions directly and indirectly caused by an activity or accumulated over the life stages of a product. A carbon footprint can be divided into 4 levels: personal, product, organizational, and country. A personal carbon footprint is a measure of greenhouse gas emissions that are a result of daily life. Examples of contributors to personal carbon footprint are clothing, food, housing, and traffic. The emissions from the entire life of a product, extraction of raw materials and manufacturing, and recycling or disposal contribute to product carbon footprint. Greenhouse gas emissions from energy used in buildings, industrial processes, and company vehicles account for organizational carbon footprints. An entire country collectively generates a carbon footprint from carbon dioxide emissions generated by the consumption of materials and energy, vegetations and other carbon sequestrations, as well as the indirect and direct emissions caused by import and export activities. Zero carbon housing is a result of the building sector being one of the largest contributors to greenhouse gas emissions in urban areas.

The calculation of the carbon footprint becomes detailed when considering secondary factors. Secondary factors involve the home’s occupant lifestyle such as diet, foods are consumed (example organic vs. non organic), frequency of yearly air travel, commuting mileage to and from work, school, etc., use of public transportation, and number, type, and use of private vehicles. Secondary factors also include fashion or type of clothes purchased and worn, frequency of recycling, recreational activities and use of financial and other services throughout a given year. The frequency of airline flights in a year is considered due to the amount of fuel consumption and other energy usage and emissions generated by one flight. A person that travels frequently may have a significantly bigger carbon footprint than someone who flies once a year for a vacation. The emissions for an individual flight are calculated by using the greater circle method. First, the distance between airports is determined. Then calculations are completed to account for indirect distances and by an emissions factor in relation to the type of flight (international or a short flight, and what class seating the person is in). Another contributing factor to a person’s carbon footprint is their personal vehicle which includes the type of car driven, the efficiency or miles per gallon (MPG) rating, and the number of miles driven each year. The frequency of public transportation used by an individual, miles traveled on public transportation and the type of public transportation used such as bus, train, or subway contributes to their carbon footprint as well. Other factors, as trivial as they might seem, are included in the calculation of a person’s carbon foot print to include things such as the type of diet. A vegetarian compared to a person that eats a lot of red meat will have a lower carbon footprint. All factors being the same except diet, a vegetarian secondary carbon footprint averages three metric tonnes of CO2, one tonne less than the individual who consumes meat. Other factors include the purchase of local and /or organically grown produce vs. imported items, the latest clothes fashions vs. more conventional purchases, buying individually packaged products vs. buying in bulk, recycling activities, and the types of recreation such as carbon-free activities like hiking and cycling or carbon-intensive activities like skydiving or boating.

Determining a zero-carbon home

• Energy efficiency: Homes have to be energy efficient and minimize the energy demand that is generated daily from a home. New homes will be required to have sufficient insulation installed and be "adequately airtight." The installation of 180mm (or more depending on climate) thick insulation, recycling of gray water, replacement of appliances with an energy efficiency rating of "A" and insulation of hot water heaters all contribute to qualifying the degree of energy efficiency.
• Carbon compliance: The onsite contribution to zero carbon includes low onsite carbon usage and zero carbon energy such as a community heating network. A community heating network or "district heating" is a system that distributes heat for residential and commercial water and space heating needs usually from a central location. This dramatically reduces the carbon footprint of individual homes. Which type of heating fuel/system used further impacts on the carbon footprint.
• Allowable measures: Any type of approved carbon-saving measures that could be used on homes consisting of on-site, near-site, and off-site options. On-site options include installation of smart appliances, use of grid-injected bio-methane, installation of site-based heat storage, etc. Near-site options include local micro-hydro schemes, communal waste management solutions, and local energy storage solutions. Off-site options include the investment in plants that turn waste into energy, investment of renovating with low carbon technologies, and investment of low carbon cooling, etc. Other alternative solutions include the development of alternative projects such as reforestation, solar, hydro, and wind power. This is known as carbon offsetting. These projects are considered carbon offsetting because they either prevent the burning of fossil fuels (solar, hydro, wind) or they utilize CO₂ from the atmosphere (reforestation) resulting in offsetting the amount of carbon released into the atmosphere by conventional fossil fuel burning methods.

Various private entities and government agencies are beginning to promote the concepts of zero-carbon homes and zero-carbon footprints. In the United Kingdom the Zero Carbon Hub helped the building of zero-carbon housing become a more common practice. The Zero Carbon Hub existed from the summer of 2008 until 31 March 2016 when the government closed it. The Zero Carbon Hub was a public/private partnership working together with the private industry and the government to help reach the government’s energy consumption reduction goals set by the European Union under the Kyoto Protocol of 1997. In the European Union, buildings are responsible for 40% of the total amount of energy needed by the European Union. This percentage is expected to rise with an increase in future building construction.

Despite UK being involved in pioneering some definitions of Zero Carbon Homes, it now appears that it will become unacceptable to market such homes using the term "Zero Carbon Home", because the UK's Advertising Standards Authority (ASA) have ruled that nothing which is manufactured can be called Zero Carbon.

Earthship Biotecture

An example of zero-carbon housing is Earthship Biotecture. Developed by Mike Reynolds, the Earthship is an environmentally friendly 100% sustainable type of home that can be built anywhere and in fact have been constructed all over the world. They are constructed with materials that would normally be discarded to take up space in a landfill including old tires, bottles, and cans. Reynolds has three requirements for the a sustainable architecture of Earthships. First, they must utilize only natural (non-manmade) as well as recycled materials. Second, they must depend only on natural ("off-the-grid") energy sources. Third, they must be financially feasible as a do-it-yourself concept, such that an average person could build their own Earthship.

Reynolds’s design was fairly simple. A southward-facing slope is used and partially excavated to nestle the back of the house into the earth and provide a thermal mass, and discarded tires and earth are used for the walls. The tires are packed with dirt to make a very dense-like brick. These "tire bricks" are strong enough to support the load of a roof structure and also very resistant to fire. Recycled cans and bottles are used as filler in the walls, sometimes with the bottles placed strategically to give an inlay glass tile look.

Earthships use water four times before it is discarded. There are cisterns at the roof level to collect rain water or snow melt. The cistern for a given Earthship is sized to the local climate. From the cistern, the water is fed into a water-organizing module with a pump and filtering device. The water is pumped into a pressurized tank to meet the building code of required water pressure. This fresh water is used for bathing, drinking, and activities like washing dishes. The water that flows from these activities is known as "gray water;” it is not sanitary for drinking, but it can be filtered and utilized for other purposes in the Earthship. First, the gray water passes through a grease filter and then collected into an interior botanical cell. A botanical cell is an indoor garden with growing vegetation. Oxygenation, transpiration, filtration, and bacterial cleansing all take place in the closed cell which cleans and filters the water. After the botanical cell the process of filtering the "gray water" is complete and the water is used to flush the toilets. The state the water is in after being used in the toilet is known as "black water". "Black water" is not reused inside the Earthship but is transferred to a solar-enhanced septic tank with leach fields and used for watering of exterior botanical cells (landscape plantings).

Earthships also have the capacity to process the wastes (generated daily by a household) in the interior and exterior of the Earthship. The exterior botanical cells reduce the waste volume leaching into the ground and reduce the risk of contaminating an aquifer. This system eliminates the use of large public sewer systems and treatment facilities that sometimes cannot adequately treat. The reuse of gray water to produce food allows the Earthships to take sustainability to the next level.

The placement of the Earthship structure into the side of a slope allows a relatively constant climate inside the home to be maintained with minimal energy usage. The earthen walls act as a thermal mass soaking up heat during the day and radiating that heat back into the living space at night. This allows the temperature of the inside of the house to stay stable throughout the day and night. Conversely, in warmer ambient temperatures, the earth-bermed house maintains a comfortable indoor temperature assisted by the relatively stable core temperature of the earth.

Earthships can live "off the grid," meaning they can produce their own electricity instead of having to rely on the current infrastructure for power. A power system that consists of photovoltaic cells and a wind power unit supply the Earthship with enough power for the daily actions/usage within a given household. The power from the wind and the solar system is stored in several deep-cycle batteries that deliver the power to the outlets as well as all of the appliances.

The Citu Home

Citu, a company working to accelerate the transition to zero carbon cities, has developed a zero-emission home in partnership with Leeds Beckett University, in part funded by Innovate UK. With the goal of creating a system able to be produced at scale to allow mass adoption, the Citu Home is built in a factory from timber-framed panels. The factory is located in the 'Climate Innovation District', an area on the outskirts of Leeds City Centre where 500 zero emission Citu Homes will be built.

The Citu Home was developed using Passive House tools to create a building so efficient that its heating needs will be on average ten times lower than a conventional house. The home does not have a gas boiler, instead it uses a MVHR system to recycle heat from people and appliances. This means the home's small heating requirements can be satisfied entirely with renewable energy. Citu supply all Citu Homes with 100% renewable energy via Good Energy, one of the UK's leading renewable electricity suppliers.

The homes timber framed design allows it to sequester several tonnes of CO2 in the building's structure, whilst the fact it is powered by 100% renewable energy for all its energy needs (including heating) means people living in it can expect to reduce their carbon footprint by over two tonnes of CO2 per year, as the average UK household emits 2.3 tonnes of CO2 heating their home.

Role in environmental governance

Zero Carbon Homes can play a considerable role in environmental governance. These structures are capable of serving the same everyday functions of a home against changing environmental conditions and are a form of engineering resilience. Engineering resilience is a part of adaptive governance. Adaptive governance is the idea that sustainability can be achieved by adapting to changes instead of changing something completely. Zero Carbon homes allow humans to adapt to the increasing global temperature. These types of homes make it possible for people to survive without the use of declining levels of fossil fuels, protects the inhabitants from food shortages, and water contamination. Zero carbon homes can provide resilience to the changes from the upset of a tipping point in dynamic stability. In this case "tipping point" represents the dangerous aspects of climate change. When a tipping point occurs the system would be subjected to a new domain of stability and the characteristics of stability will have changed. The system will have entered into a new "domain of attraction" and the system will be attracted to a new resting place. In the idea of this, the height of the valley that the "domain of attraction" is in determines the amount of stress or disturbances needed to force the system into another valley or "domain of attraction". Zero carbon homes provide engineering resilience to this event because they will be able to cope with the disturbances that occur. Exactly when these "tipping points" are going to occur is almost impossible to know and difficult to predict. They represent non-linear change, making it difficult to predict or prepare for.

Possible complications

·Affordability: The Net Zero home, though affordable in the long run, may be quite an investment in the beginning. Much of the equipment used in the production of Net Zero housing is expensive. Aside from the solar panels which are an investment of their own, consumers have often settled for less square footage in an attempt to balance out the overall expenses. As far as implementing Net Zero building on a large scale goes, funding will become an issue as building size increases due to cost.

·Energy Production: One of the most important factors in the construction a Net Zero structure is the amount of energy it will save in comparison to the previous structure. Any Net Zero building needs to be able to function at the same capacity at which it had prior to the retrofitting. This means that each structure will need to produce enough energy to sustain itself or else it will be pulling energy from the general grid. Net Zero homes are most commonly fitted with solar panels as the main energy production source on the roof of the structure. This means that as the height of a certain structure increases, the surface area on the roof becomes smaller in comparison to the overall volume of the structure. Complications concerning energy production will arise due to the fact that there will not be enough space for solar panels to meet the consumption needs of the structure.

·Predictability in Relation to Surrounding Environment: As the concept of Net Zero building spreads throughout the world, problems with energy production are becoming present aside from size of the structure. The region in which a certain Net Zero home is built in directly effects its energy production. Complications appear amongst the rural community due to the fact that rural areas are often heavily wooded. In order for a solar panel to function to its full potential, it requires direct sunlight for as many hours out of the day as possible.

See also

• Net energy gain
• Zero heating building
• Zero-energy building