Skip to Content
U.S. Department of Energy Energy Efficiency and Renewable Energy

Building America Advanced Technologies and Practices

Drawing of a birds-eye view of a group of homes all in gray, with a home in a different color (green) standing out from the others in the center.

Since 1995, the U.S. Department of Energy's Building America program has provided research and development of building innovations to the residential construction and remodeling industry. As a national center for world class research, Building America develops market-ready solutions through partnerships with building and remodeling industry leaders, nationally recognized building scientists, and the national laboratories.

Here you will find real-world examples of Building America innovations that offer technical and business solutions for builders that help them reduce costs and deliver healthy, durable, high performance homes to their customers. The following case studies include innovations in a variety of climate regions for:

Building Science Solutions

Ducts Inside Conditioned Space

Installing the ducts inside the home's thermal envelope instead of in an unheated attic or crawlspace can provide significant energy savings and other benefits. Methods for installing the ducts in conditioned space include: between floors in open-web floor joists, in dropped ceilings, or in sealed insulated attics or crawlspaces. Building America recommends this energy-saving practice to builders as a way to reach high performance goals, and has tested these options in field projects with several builders, as described in the following case studies.

Unvented Attics

Insulating the attic along the roofline is one option for builders who want to install their HVAC equipment and ducts in conditioned space, but who prefer to keep the HVAC equipment in the attic due to floor space or noise concerns. Building America researchers worked with builders in several climate zones to identify combinations of materials that worked appropriately given the climate conditions.

Unvented Crawl Spaces in I-Code

Building America research encourages the use of slab-on-grade foundations rather than crawlspaces for locations that are not subject to frequent flooding. For builders who do use crawlspace foundations, Building America researchers investigated climate-related moisture problems and determined that sealed, insulated crawlspaces perform better than vented crawlspaces in humid climates.

Simplified HVAC Distribution

The traditional HVAC installation for homes with poor insulation and single-pane windows has been to place heating registers along outside walls to warm infiltrating air and cold walls. With the advent of a highly insulated building envelope and double pane windows, Building America recommends a simplified duct distribution system using a central trunk line and short branch ducts, properly sized ducts, hard-ducted central returns on each floor, and transfer grilles or jump ducts for pressure relief. These systems are simple to install, economical, and provide better air flow; also, they are less likely to be compromised due to improper support of lengthy duct runs or damage during installation. The following case studies describe builders around the country who are improving the designs of their duct systems.

Buried/Encapsulated Ducts

If it is not possible to locate ducts in conditioned space when upgrading existing homes, one option is to install the ducts in the attic and then bury them in blown cellulose or fiberglass, or cover them with spray foam. The ducts should be thoroughly sealed with mastic, insulated with a duct insulation that includes a vapor barrier, and compactly laid on the attic floor (preferably running parallel to the truss chords), then completely covered with insulation.  Building America research showed this to be a viable option in dry climates; in humid climates, it should be avoided due to condensation concerns.

Back to Top

Energy Efficient Components

Night Ventilation Cooling

Building America research showed that using night cooling could reduce cooling energy use up to 35% in locations where summer temperatures vary by 30°F or more between day and night. Night cooling systems developed by Building America researchers consist of temperature- and timer-controlled dampers that open to allow outside air in through fresh air intakes ducted from an outside vent to the return side of the air handler. The cool air is drawn in by the air handler fan and distributed throughout the house to provide cooling when the air conditioner is not running. Because the system is automatically controlled, it doesn't rely on house occupants to turn switches on or off; also, it is safer than leaving windows open at night.

High R-Value Walls

The building envelope—which consists of the insulation layer, air barrier, and vapor retarder of walls, floors, and ceiling—plays a critical role in creating a comfortable, healthy indoor climate. Building America researchers work with builders to conduct field projects to determine the best combinations of materials and techniques for high-performance building envelopes in different climates. These studies are performed on a variety of wall types, as well as insulation and wall cladding. Researchers have concluded that the rated R-value of the wall insulation is not the only or most accurate measure of wall performance; moisture management, air leakage control, and thermal bridging are critical factors in performance. The entire wall assembly must be correctly installed to shed bulk water, minimize vapor transport, prevent condensation and trapping of moisture, reduce thermal bridging, and provide a continuous air barrier that is correctly aligned with the thermal barrier. The following case studies provide details about builders that are achieving high-performance walls in every climate zone.

Back to Top

Assured Health, Safety, and Durability

Moisture-Resistant Wall Theory

Techniques used to prevent walls from getting wet also prevent them from drying out—a popular option, installing polyethylene under the sheetrock, is a good example of this. Building America researchers conducted experiments where different configurations of building papers, sheathings, and claddings were evaluated for rainwater and vapor control. Results from these tests led to the development of recommendations for rainwater control in a variety of building assemblies. In addition, data from instrumented test walls were used to determine boundary conditions for hygrothermal modeling to develop climate-specific recommendations for vapor control with the use of insulating sheathings. These recommendations were drafted into code language and submitted as a code change proposal by DOE for the 2009 ICC code development cycle. They were also recommended to builders participating in Building America field studies.

Simple Residential Ventilation Systems

Building America researchers have developed a simple, less expensive alternative to heat recovery ventilators for bringing fresh air into new, air-tight homes. Fresh outside air is drawn in through an air intake ducted from an outside vent to the return side of the furnace air handler. The air is drawn in by the air handler fan and is filtered and distributed throughout the house. An electronic controller equipped with a timer and/or temperature and humidity sensors controls a damper on the fresh air intake, and also operates the fan to provide ventilation during periods when the furnace or air conditioner aren't operating. The success of this option depends on high-efficiency fan motors, proper duct sizing, proper placement of the air intake at the air handler, and proper setting of controls to avoid over-ventilating in humid climates. The lowest cost ventilation solution is exhaust-only using quiet, efficient bathroom or kitchen exhaust fans that are set to provide intermittent or continuous exhaust that meets ASHRAE 62.2 requirements. This option is not recommended in homes in humid climates or homes containing combustion appliances that are not direct-vented because of the likelihood of depressurizing the home.

Back to Top

Whole-House Packages

New Homes

In 2005, the Building America program set a goal of proving that cost-neutral energy savings of 40% over code were possible at a production scale for new home builders in every U.S. climate zone. Between 2005 and 2010, Building America worked with 34 builders to construct nearly 3,000 homes in communities of at least 10 homes each (and in many cases more than 100 homes per project). Using a whole-house approach and tradeoff analysis to find cost-effective solutions, Building America research teams worked with the builders to design packages of energy-efficiency measures that worked together to meet the high-performance target. Each home achieved a HERS score of 70 or better while reducing energy costs to the point that utility bill savings would more than make up for any increased first cost. In every field study, homeowners made a net profit from the first year.

Existing Homes

More than 70% of the U.S. housing stock was built before 1990, i.e., before modern building codes were in place. Building America has worked with several builders on retrofit projects, applying a whole house approach to achieve the most cost-effective energy savings possible, while avoiding safety, moisture, or durability issues. Building America produced a reHabitat Guide for Habitat for Humanity affiliates. Other projects have included working with utilities such as the Sacramento Municipal Utility District (SMUD) on foreclosures and providing design recommendations and analysis to builders who turned from new construction to gut-rehabs and energy-efficient remodels during the economic downturn.

Back to Top

Utility Program Support

In markets with constrained energy generation capacity, the amount of peak-load reduction is as important as the amount of total energy saved. This enables utilities to establish market-based incentives that can help builders further meet business goals. For real world examples, read the following case studies.

To learn about additional building technology solutions in various climate regions, visit the guides and case studies Web page. You may also explore a variety of technical publications on these innovations in the publications library.

Back to Top