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use and lower building energy consumption, reduce the achieved net-zero with 6 more anticipated to achieve net-
associated carbon emissions, and minimize resource zero energy status (Hewitt and Hobart, 2012). 32 buildings
wastage through sustainable design and construction were verified as net-zero energy in 2014 (Cortese and
(Mehta et al., 2013). Higgins, 2014) which shows that more buildings in the US
are working towards net-zero energy status.
Most buildings are inefficiently operated which causes
energy wastage and increases greenhouse gas (GHG) This paper presents the US perspective on the move
emissions to the atmosphere (IPCC, 2014). Since towards net-zero carbon buildings. It discusses the
buildings consume nearly a third of global final energy concept of ‘net-zero’ in the US in relation to carbon,
use, reduction of energy use in the building sector energy and exergy, and focuses on how net-zero energy
has the potential to bring about significant energy strategies can drive towards attaining stringent carbon
savings and reduction in CO2 emissions. CO2 constitutes reduction targets that have been set. The case studies
the largest percentage of GHG emissions as shown in illustrate some of the strategies that have been adopted
Figure 1, so reducing CO2 emissions can lead to a huge in an effort to achieve net-zero energy in buildings in the
reduction in GHG emissions. Several targets have been US and provides some recommendations.
set for countries to meet stringent energy use reduction
requirements. Various initiatives have been created
nationally and internationally to meet these targets. For Methodology
example, the Department of Energy (DOE) in the US set The approach adopted in developing this paper involved
a goal to reduce carbon emissions by 3 billion metric examining various aspects of net-zero buildings, from
tons by 2030. This includes focusing on the reduction a general viewpoint, and then focusing on the US
of carbon emissions from the building sector (Office of perspective. The research methodology involved a review
the Press Secretary, 2015). In the United Kingdom (UK), of literature on current trends in net-zero energy in the
the government set a goal in 2010 to reduce the central US and case studies of buildings that have achieved net-
government’s carbon emissions by 10% in 12 months. zero energy status. 3 case studies of buildings in the US
They exceeded the goal and achieved a 13.8% reduction were conducted to illustrate the developments that have
after 12 months (UK Government, 2011). been made, the technologies adopted to attain net-zero
status, and the associated benefits. A study of some of
In general, there is growing interest in net-zero carbon the technologies employed was carried out and critical
or net-zero energy buildings. Net-zero energy buildings performance data was obtained from available public
are those that produce as much energy as they consume, records. Discussions were held with building energy
which could result in a reduction in GHG emissions. experts―these proved helpful in summarizing the case
study projects.

The first case study is a new build, the National Institute
of Standards and Technology (NIST) building, which is
a net-zero energy residential test facility where various
alternative energy and high-efficiency systems are
tested (NIST, 2015). It demonstrates the possibility of
attaining net-zero in a residential building. The second
case study is the Morning Star and Hybrid Renewable
Energy Systems (HyRES) Lab constructed for the solar
decathlon―a net-plus small experimental building which
produces more energy than it consumes. The third
case study is the Integrated Design Associates (IDeAs Z
Squared) commercial office building retrofit, with various
strategies to attain net-zero status. A detailed description
of these cases is presented later in the paper to highlight
the approaches implemented in achieving net-zero status.

Net-Zero Carbon Buildings
Figure 1 Carbon dioxide emissions in 2013 (Courtesy
Architecture 2030 (2014) defines a carbon neutral
of the US EPA, 2015)
building as a building that is designed and constructed to
require a greatly reduced quantity of energy to operate,
More government institutions, private businesses, and
meeting the balance of its energy needs from sources
individuals are taking up the challenge and working towards
that do not produce CO2 emissions and therefore result in
net-zero status for their new buildings or in retrofitting
zero net CO2 emissions.
existing buildings to achieve net-zero energy status. A
number of these have been verified as net-zero. As at 2012,
21 commercial buildings in the US were identified―15 had

ZCB Journal 2015 • Volume 4 23