In 2015, 40 percent of U.S. energy was used in residential and commercial buildings (11,430 terawatt-hours). Of this total, residential buildings account for 54 percent and commercial buildings 46 percent.
About half the operational energy in U.S. homes and businesses goes toward heating, ventilation, and cooling (HVAC), which employ natural gas, electricity, and, in some areas, oil. The next biggest energy uses are for lighting, which is nearly all electric, and for heating water, which typically uses natural gas and electricity. Energy use within buildings also includes electronics (electricity), refrigeration (electricity), and cooking.
Building construction also requires significant amounts of energy usage: the total amount of energy embodied in the construction and maintenance phases may account for 20 percent of a building’s lifetime energy use, and even higher in efficient, low-energy buildings.
Energy is used in the manufacturing of components and materials (coal, oil, natural gas, electricity), in the transportation of materials and workers to the construction site (oil), and in the construction process itself (electricity, oil). Steel, concrete, wood, copper, glass, paint, insulation materials, sheetrock, and aluminum all require energy of different kinds and amounts in their manufacture.
The buildings sector offers many significant opportunities for improved energy efficiency—both in operations and in construction. Heating and cooling could in most instances be electrified and made more efficient by the use of air-source and ground-source heat pumps, while the need for heating and cooling could be reduced by better design and the use of more insulation. Buildings could also be designed and materials selected to optimally balance embodied energy and operational energy needs (e.g., by designing for passive lighting, heating, and cooling).
Example: A Suburban Home
The typical suburban American home was constructed sometime during the past 30 years according to building standards that assumed the home’s occupants would have unlimited access to cheap, fossil-fueled energy.
The building uses external energy sources to heat, cool, and move the air it encloses; to light its rooms even during daytime hours on sunny days; and to heat its own water quickly and at any time. The building was designed, in essence, merely to enclose space as cheaply as possible, with all amenities provided by machines consuming energy from external sources, most tracing back to fossil fuels.
About the only nod to energy efficiency during the building’s construction phase was the use of R-20 fiberglass insulation in the walls and ceilings. Even in temperate zones, the house may cost hundreds of dollars per month to heat in the winter and cool in the summer. The home is likely heated with natural gas and cooled using electricity.
Daylight enters through windows, but there typically has been no systematic and deliberate effort to maximize the practical use of daylight through southern orientation of the building’s windows, or the installation of skylights or solar tubes. The lighting in the house, at least, is provided by energy-efficient, compact fluorescent bulbs as these have been standard and affordable for years.
Most homes are constructed with a standard set of materials: plywood and particle board (production of which often contributes to deforestation and results in emissions from particle matter, veneer dryers, and adhesives); PVC (made from natural gas and natural gas liquids); concrete (whose key ingredient, cement, is carbon-intensive and is made using coal); vinyl (made from natural gas or natural gas liquids); steel (coal is used in the early phase of production); copper (oil is used for mining the ore, coal for smelting); and glass (coal or natural gas is used to produce high temperatures). Each construction job generates a heap of unusable scraps that has to be taken to the landfill for disposal.
In addition, many conventional building materials now originate in China, where they are manufactured more cheaply. The United States formerly led in the production of all these materials, but for many years now most American building materials companies have sourced their products from overseas—requiring transport over thousands of miles using diesel-powered trains and cargo ships.
Most houses start with a concrete foundation pour. A framework of steel rebar (likely produced in China using coal) is laid, over which the concrete is poured.
To make cement, limestone and other clay-like materials are heated in a kiln at 1400 degrees C (usually using coal as a heat source) and then ground to form a lumpy, solid substance called clinker, which is then combined with gypsum. Altogether, the cement industry is responsible for five percent of global greenhouse gas emissions, with each ton of cement responsible for about a ton of carbon emissions.