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December 1, 1999
Building America is a program of the U.S. Department of Energy, in which teams of architects, engineers, builders, equipment manufacturers, and others collaborate in a systems engineering approach to produce homes that use up to 50 percent less energy to operate. The Building Science Consortium, one of five Building America teams, employs an integrated strategy to achieve the Building America goals, incorporating advanced framing, improved insulation, simplified HVAC systems, high performance windows, and details that ensure durability of the homes. The consortium’s projects to date, totaling 884 homes, have produced in significant and measurable environmental gains. Click here for more information about Low Energy Buildings and Energy Efficient Retrofits.
About the Building America Program
Building America is an industry-driven, private/public partnership sponsored by the U.S. Department of Energy to accelerate the development and adoption of innovative building processes and technologies for production housing. The goal of the program is to produce resource-efficient, environmentally sensitive, affordable, and adaptable residences on a community scale. Building America unites segments of the building industry that traditionally work independently of one another into teams of architects, engineers, builders, equipment manufacturers, and others, to collaborate in a systems engineering approach to achieve the following objectives:
- Produce homes on a community scale that use 30 to 50 percent less energy.
- Reduce construction time and waste by as much as 50 percent.
- Improve builder productivity.
- Provide new product opportunities to manufacturers and suppliers.
- Implement innovative energy- and material-saving technologies.
Currently, there are five teams comprising more than 180 different companies. The teams have built close to 1,500 homes to date.
The Systems Engineering Approach
Throughout the design and construction process, the systems engineering approach considers the interaction between the building site, envelope, mechanical systems, and other factors. It recognizes that one feature of the house can greatly affect others and it enables the teams to incorporate energy-saving strategies at no or minimal extra cost.
Building America teams work to produce houses that incorporate energy- and material-saving strategies from the very start of the building process—the design. Initial costeffective strategies are analyzed and selected during pre-design. The team then evaluates its design, business, and construction practices to identify cost savings, which can then be reinvested to improve energy performance and product quality.
After the design has been evaluated, the team builds a prototype or “test” house. After a test home is built, the team performs field tests and sets up long-term monitoring. Then DOE’s National Renewable Energy Laboratory provides feedback on energy technologies and design strategies implemented by the teams. The results are documented in case studies that enable builders to learn from each other. The Building Science Consortium has adopted from the outset a philosophy of shared information and has chosen not to make its findings proprietary. Consortium members share the goal of disseminating good practice throughout the industry.
After the prototypes are tested and the team makes any changes to the design needed to increase efficiency and cost-effectiveness, the design is retested before it is used in production or community-scale housing.
This approach offers numerous advantages to the builder:
- Reduced construction costs;
- Improved productivity;
- Improved building performance;
- Reduced callback and warranty problems;
- Competitive advantage.
There are also significant advantages to the consumer:
- Increased quality without increased cost;
- Increased comfort and performance;
- Reduced utility bills;
- Access to innovative financing due to predictably lower utility bills.
The Connection with Energy Star Homes
Energy Star Homes is a cooperative program of the U.S. Department of Energy and the U.S. Environmental Protection Agency. Energy Star Homes are built to a set of prescriptive standards and then tested to ensure that they have achieved the performance target of 30 percent less energy use for heating, cooling, and water heating than a reference home based on the Model Energy Code.
Building America homes must, at a minimum, meet the same performance standard as Energy Star Homes and, having done so, may carry the Energy Star rating. However, the Building America program is entirely performance-based.
The Building Science Consortium
The Building Science Consortium (BSC) has designed cost-effective, resource-efficient single- and multi-family homes for each of the five U.S. climate types.1 BSC builder partners have committed to building close to 4,000 Building America homes in 17 communities; more than 800 of these were completed and another 300-plus under construction as of March 2000. Re-engineering and design is underway in eight additional locations.
II. BSC's Approach
BSC’s basic approach is to invest more money to improve the building envelope while saving by downsizing the mechanical equipment, so that the total construction cost remains roughly the same. BSC has established performance metrics that allow the prediction and quantification of building performance. BSC has developed construction techniques, equipment, and systems to allow production home builders to meet these performance metrics at little or no incremental cost.
Integrated Construction Strategy
The Building Science Consortium employs an integrated strategy to achieve the Building America goals:
- Using advanced framing/optimum value engineering;
- Incorporating higher levels of insulation and better installation details;
- Simplifying heating, ventilating, and air conditioning systems;
- Reinvesting energy cost savings in high performance windows and other advanced building features;
- Incorporating details that ensure durability of the homes.
Advanced Framing. BSC uses advanced framing and insulation methods to increase efficiency and comfort while decreasing costs. Although advanced framing has been around for 30 years, it has—with some limited exceptions—not been widely adopted. BSC believes this is due to a lack of systems integration. BSC has integrated advanced framing into a complete approach to building envelope design and mechanical system layout, using modular dimensioning, detailed construction drawings, and structural mock-up testing to refine an updated approach to advanced framing.
On many Building America projects, BSC has used 2x6- instead of 2x4-inch studs, set 24 instead of 16 inches apart. This allows room for more and thicker insulation, enhances the strength of the house, and reduces thermal bridging. It also reduces the amount of framing wood and, because 30 percent fewer pieces have to be assembled, framing takes less time and labor costs are significantly lower.2
Working with the U.S. Army’s Civil Engineering Research Laboratory, BSC is facilitating code approval of new advanced framing techniques by jurisdictions subject to severe earthquake and wind loads. Full-scale assemblies are being tested under the new seismic loading protocols developed after the 1994 Northridge, California, earthquake.
Tightly Sealed House Envelopes. To construct a tight thermal envelope, BSC has put a great deal of effort into air leakage control, identifying and eliminating large holes, and developing innovative closure details. Oriented strand board has been replaced with rigid foam exterior sheathing. The insulation board joints are taped, or a system of vertical panel laps and horizontal flashings is used, to create an exterior air barrier as well as a drainage plane for rain control. This eliminates the need for building paper or housewrap.
In cold northern locations, BSC has sealed and insulated interior basement walls with R-7.5 rigid polyisocyanurate board or with “wrapped batt” insulation. Other interior insulation systems are currently being tested for cost-effectiveness. Interior basement insulation helps prevent heat loss and reduces chance of condensation-related mold problems.
Simplified Central HVAC System. BSC has moved the ducts into the conditioned space, eliminating heat loss to the exterior and limiting the temperature difference at the ducts. This, along with placing the heating/cooling system in a central location, shortens duct runs and cuts material and installation costs—sometimes by more than 50 percent—also saving energy. Some homes also use new round ducts only 8 inches in diameter, which are cheaper to install and easier to maintain.
BSC’s building envelope designs for hot-dry and hot-humid climates, with ductwork and air handlers located within the conditioned space/building pressure boundary, have led to subsequent innovations in roof insulation systems and building code changes. The unvented roof designs developed for hot-humid climates (see Figure 1) significantly reduce latent loads (moisture) and allow the use of simple off-the-shelf components to provide controlled ventilation with dehumidification.3 . .
Download complete report here.
- BSC’s climate types are based on Herbertson’s Thermal Regions, a modified Koppen classification, the ASHRAE definition of hot-humid climates, and average annual precipitation data from the U.S. Department of Agriculture and Environment Canada. (A map is shown at www.buildingscience.com/buildamerica.html.)
- Considering both materials and labor, BSC’s approach to advanced framing on BA homes has
typically reduced framing costs by $250 per house. See Tables 2 through 5.
- Unvented roof designs are currently only recommended with tile roofs. Unvented asphalt shingle
roofs are being tested for loss of roof life.