Zero-carbon footprint and net-zero energy
The terms zero-carbon footprint and net-zero energy mean essentially the same thing. Since even a single light bulb uses electricity (which is a form of energy) a house can never use zero energy. However, since you can generate electricity from solar panels it is possible to have a house that generates all of the energy it uses over the course of a year. If you generate enough energy to power your home every single day of the year then you have gone “off grid”. If you generate as much energy as your house uses over the course of a full year, but not every day, then you have a net-zero energy house which, unless you are able to read in the dark, will require a connection to the grid via a net meter so you have power, and light to read by, at night. If the energy used by the house is all generated by zero-carbon sources (such as solar panels or a wind turbine) then the terms net-zero energy and zero-carbon footprint mean the same thing. In theory, if you used a diesel-powered generator to make all the electricity your house used (and that was all the energy your house used) then you would have a net-zero energy house, but this is not usually how the term is used. In common usage a net-zero energy house means a house which generates all its energy on site and that energy is made from zero-carbon sources like solar panels or wind turbines. Hence it is equivalent to a zero carbon house.
PassivHaus (Passivehouse), PHIUS
PassivHaus is a standard for low-energy or zero-energy houses. It was developed in Germany by the PassivHaus Institute. There is a U.S. branch of the PassivHaus Institute called the Passive House Institute US or PHIUS. PassivHaus certification requires compliance to their exacting standards for both building materials and methods of construction as well as the final result in terms of energy efficiency. Every element of the construction must be audited back to its source. The PassivHaus standard for total energy use is 60 kilowatt-hours per square meter of floor space per year. This is equal to 5.6 kWh per square foot per year. If your house has 2,500 square feet of living space then your total energy budget to meet the PassivHaus standard (including heating fuel like natural gas or heating oil, plus your electricity use) is about 14,000kWh per year. The average U.S. house uses about 11,000kWh per year in electricity alone. When you add in the extra energy used to heat the home, often five times the amount of energy used in electricity, the average U.S. house uses about 500% more energy than the PassivHaus standard.
After we installed the fab four (insulation, heat pumps, solar panels and triple-glazed windows) our house is using about 6.5 kWh per square foot per year or only about 16% more than the PassivHaus standard. This is a remarkable result given that the Passivhaus standard was created for new houses and our house is a 1970’s design with no sealing of the walls against air infiltration and with only average insulation in the walls. Zero Carbon Home and PassivHaus have similar approaches to reducing energy consumption such as better insulation, low-E triple-glazed windows, heat pumps and solar panels. But because of the prescriptive details and audit trail on building components required by PassivHaus it is almost impossible to apply it to the renovation of an existing house and it is only applicable to new construction. It is both expensive and time consuming to do the audit.
LEED (Leadership in Energy and Environmental Design) Certification
LEED Certification is a program of the U.S Green Building Council and is somewhat similar to the PassivHaus standard except it provides more flexibility on reaching overall energy efficiency performance rather than requiring the strict adherence to the prescriptive building elements of the PassivHaus standard. However, LEED does not currently offer a standard for renovating an existing house, it only applies to new construction. The LEED system has been criticized for making money for the Green Building Council that runs it rather than actually cutting costs or carbon footprint, see this article that was recently published: