A green home is an intricate system made up of interdependent components. Changing one aspect of this system can create a ripple of effects in other areas. Builders were reminded of this when they began building tighter houses in the 1970s in response to rising energy costs. Tightly sealing the thermal envelope reduced heating and cooling costs but sometimes had unintended results, such as increased indoor air pollution due to inadequate ventilation or problems with mold due to moisture trapped within the structure.
The solution was not to return to the days of leaky, uncomfortable houses that wasted energy. Instead, what grew out of this experience was a new approach to home building, called the whole-house systems approach. In collaboration with building-science researchers, home-building associations and government agencies such as the U.S. Department of Energy’s Building America program, many home builders across the nation are now successfully using this approach. It emphasizes strategic planning, systems analysis, and testing and verification to ensure that improvements in one area won’t jeopardize health, safety, affordability, durability, profitability and other vital concerns.
Ideally, home builders should incorporate green building into their practices as part of this whole-house systems approach. This requires taking into account the interaction of many factors: the building’s structure and thermal envelope; heating, cooling, water heating and electrical systems; renewable energy systems; the site’s climate, topography, landscaping and surrounding structures; aesthetics; health and safety requirements; and how the occupants will use the house.
For example, a green builder concerned with improving the performance of the whole house will not merely select a more energy-efficient heating and cooling system and call it a day. Instead, the builder will look for opportunities to improve the thermal envelope and decrease heating and cooling loads, such as by reducing air leakage, designing and locating ductwork to minimize energy losses, increasing insulation, and choosing low-e windows. These improvements may allow the use of significantly smaller—and less costly—heating and cooling systems. Properly sized HVAC systems also lower the owner’s energy costs and provide greater comfort within the green homes.
According to Building America, a whole-house systems approach can reduce the energy consumption of new green homes by as much as 40% with little or no effect on the cost of construction. Usually the decisions made as part of a whole-house approach yield multiple benefits. For example, framing the home with 2x6 studs spaced at 24 inches allows increased insulation compared to conventional 2x4 studs spaced at 16 inches. Increased insulation saves heating and cooling energy and improves comfort. Also, as mentioned above, it may allow the downsizing of heating and cooling equipment. What’s more, the 2x6 framing technique reduces wood use and labor costs.
The whole-house systems approach requires that the design and construction process be highly integrated.