Existing Housing Stock—A Massive but Challenging Opportunity for Energy Savings

According to the U.S. Department of Energy (DOE), residential housing units account for 22 percent of the total primary energy usage in the U.S.¹ The average age of a single-family home in the U.S. is 34 years old, meaning that much of the existing housing stock was constructed in an era that offered both relatively inexpensive energy and did not consider carbon dioxide as a form of pollution that contributes to global warming. Consequently, simple energy-efficiency measures are sorely lacking in these homes— a problem with far-reaching consequences, but also an opportunity for substantial energy savings.

Buildings, in general, represent a substantial amount of energy requirements in the economy, making them of critical importance in reducing greenhouse gas emissions. Many experts and studies have weighed in on that point. “Improving the efficiency of buildings, which account for 40 percent of U.S. energy use, is truly low-hanging fruit,” maintains former U.S. Secretary of Energy Dr. Steven Chu. Global management consulting firm McKinsey and Company says, “Energy efficiency offers a vast, low-cost energy resource for the U.S. economy, but only if the nation can craft a comprehensive and innovative approach to unlock it.”

According to a study by the Regulatory Assistance Project (RAP),² a global, non-profit team of experts focused on the long-term economic and environmental sustainability of the power and natural gas sectors, “retrofit improvements to the heating and cooling systems of existing homes and their thermal envelope (e.g. by increasing insulation levels and reducing air leakage) present major opportunities for cost-effective investments in efficiency.” In fact, the RAP study maintains that “roughly half of all efficiency and/or carbon emission reduction potential in North American and European buildings is associated with retrofit improvements to existing homes.”

General, fundamental rules on retrofitting a house do exist; however, many different improvements can be applied, with the optimum solution typically predicated on the previous conditions of the house and on the climate zone where the house is located. In cold climates with high heating loads, measures that reduce those loads such as air sealing, adding insulation, and improving the energy performance of windows may be good first steps. In warmer climates, plug loads such as appliances, electronics, and lighting can be relatively more important, and taking action to reduce these will be more appropriate.

Software Base line Scenario Inputs

INPUT PARAMETER	INPUT CHOSEN
Location	West Lafayette, Indiana, USA
Square footage	266 m2
No. of Bedrooms	3
No. of Bathrooms	2
Age	86 years
Heating set point	21° C
Cooling set point	24.4° C
Humidity set point	50%
Walls	Wood stud, uninsulated, 40.6 cm
Exterior finishing	Wood, medium/dark
Unfinished attic	Uninsulated, vented
Finished roof	Uninsulated
Roof material	Asphalt shingles, dark
Finished basement	Uninsulated
Carpet	60% of the floor area
Windows	Single-pane, clear, non-metal frame
Air leakage	10 ACH50
Refrigerator	Energy Factor (EF) = 14.1, top freezer
Cooking range	Electric
Dishwasher	None
Clothes washer	Standard, MEF = 1.41 ft3/kWh-cycle
Clothes dryer	Electric
Lighting	20% fluorescent
Central air conditioner	SEER 10
Furnace	Gas, 80% AFU E
Water heater	Gas standard (EF = 0.59, 151 liters)