And It’s Affordable...
Building an Energy Efficient Home in Lincoln
Almost everyone agrees with energy efficiency in principle. When the simple payback is just a few years, investing in efficiency is advantageous because you permanently reduce your energy bills and can therefore enjoy many years of savings. These savings can be attractive to low- and moderate-income families because they typically pay more of their disposable income for energy bills than do families with higher incomes. The problem is overcoming the hurdle of initial cost so these families can afford the purchase.
NEO had two goals in sponsoring the Lincoln prototype:
In the vernacular of homebuyers, affordable housing is for lower- and moderate-income families. For homebuilders, however, the language is more precise because they target their products for specific buyers.
In Nebraska, affordable housing generally is for buyers who receive some type of government assistance for their purchases. Usually the eligibility criteria are for buyers who make a percentage of median income in the state. For example, eligibility for U.S. Department of Housing and Urban Development (HUD) Section-8 housing is about 50% of the median income. For the Green Built Home in Lincoln, the buyers received a low-interest mortgage through a combination of state, city, and federal homeowner financing.
Nebraska Green Built Homes
The Nebraska Energy Office has experience with the cost conundrum of residential energy efficiency. In the mid-1990s, NEO managed a successful energy efficient mortgage program. Energy efficient mortgages generally take the reduction in energy bills into account when qualifying homebuyers for their loans. Professional home energy raters test the energy efficiency of participating homes, and based on these tests, estimate the utility bills. This way borrowers can increase their mortgage premiums with confidence in keeping their overall bills the same.
According to Lynn Chamberlin, agency lead for NEO's participation in the Nebraska Green Build Program, energy efficient mortgages became popular in Nebraska once homebuilders discovered the advantages they provided their customers. By 1996 and 1997, the program was fully subscribed. Realizing they had discovered a market niche that could become profitable for them, builders approached NEO about developing a Nebraska-specific "green homes" program. By certifying the energy efficiency with a trademark that buyers and sellers alike would trust, they reasoned that energy efficient homes could distinguish themselves from those built with standard construction techniques in the market for new homes.
In 2000, a group of homebuilders in Lincoln began discussions with the NEO about beginning the Nebraska Green Build Program. In May of 2003, the program certified the first three demonstration homes in Lincoln. The first homes to participate were custom-built with high-end price tags between $250,000 and $400,000.
Today the program has grown across the state and is managed by the Nebraska Green Building Council as well as NEO staff. Nebraska Green Built Homes are built by homebuilders that have been certified by the program after undergoing training and testing. Each of the homes is inspected and their plans reviewed for compliance as part of the certification. Each must obtain a 5-star rating by a professional home energy rater.
Energy is only part of certification for a Nebraska Green Built Home. There are also requirements to use local materials; recycled content; low water consumption; and non-volatile chemicals in paints, carpeting, and finishes for a healthy indoor air quality. Unfortunately, building materials are not produced in all parts of the state and are not always available locally. At today's prices, materials made with recycled content are often more costly than conventional construction materials. As a result, energy efficiency plays a key role in making these "green" homes cost effective.
Partnership with DOE's Building America
By 2004, NEO was ready to attempt to expand the market segments participating in the Nebraska Green Build Program, starting with affordable housing. The rationale is that energy efficient homes sell because of their low and predictable energy bills. If the homes could be built very efficiently using cost-effective recycled and local materials, they could still certify as Nebraska Green Built Homes.
In 2003, NEO was awarded a federal grant for $99,334 from DOE's Building America Program through the State Energy Program to build a prototype home that would cost no more than one using standard construction techniques. This grant helped to defray some of the costs of design, evaluation, testing, and post construction that validated the energy performance and costs to build this home. Construction began in September 2004.
The results are impressive. The Lincoln prototype house contains 1,248 square feet of finished living area and costs less than $150,000 to build. These costs, about $120 per square foot, are typical for homes built using standard construction techniques for the affordable housing market in eastern Nebraska.
The estimated yearly bill for heating and cooling the prototype house in Lincoln is $356. This is $600 per year less annually for heating and cooling a house of the same size built to code. Says Chamberlin, "There are a lot of families in Lincoln who pay as much every month for their utility bills as the owners of this house will pay in a year."
Features of the Lincoln Affordable Green Built Home
So how do they build a home that is 40% more energy efficient than a conventional home built to the standards of a local energy code and not spend more to build it?
The Systems Approach to Single-Family Homes
Building America's systems engineering approach considers the interaction between the building site, envelope, and mechanical systems throughout design and construction. This approach recognizes that features of one component in the house can greatly affect others and seeks to maximize the energy performance of the home as a single system.
NEO's Lynn Chamberlin says that taking this approach to home building is the biggest single step for them to certify a home under Nebraska's Green Build Program. "So often homebuilders offer potential buyers a menu of options; windows of different sizes and quality; heating units with different efficiencies, etc. These houses then become a motley collection of components that are not optimized either for energy performance or cost."
The systems approach also demands greater attention to design and testing results. Designers using this approach carefully run computer energy models to compare the effects of changing components or design. The Nebraska Green Build Program also requires testing the performance of the home after construction is complete to certify that it is performing as expected. The tests on this home included measuring air infiltration with a blower door, duct leakage, hot air stratification with (HOBOS) temperature measurements, and pressure differentials in bedrooms. The Home Energy Rating System (HERS) score of this home was 88.1, compared to the Building America benchmark home, which had a HERS score of 78.2.
Based on testing by home energy raters, the prototype home consumes 24% less energy than a typical home built for the affordable housing market in Nebraska.
Value Engineering the Framing
One of the big savers in this project was the result of a design process called value engineering applied to the framing. Value engineering refers to a process of reducing the costs of components through optimizing their performance. Here, the builder used 2 x 6 in. lumber in the framing spaced apart every 24 inches instead of 2 x 4 in. lumber spaced 16 inches apart.
The builder used pre-engineered trusses to support the roof instead of standard trusses made from 2 x 4s. This allowed CARB to specify trusses that make room for insulation at the corners where the trusses meet the walls. This location is often a "cold spot" in standard construction where insulation is crumpled or falls away from the corner.
Value engineering greatly reduced the amount of lumber and saved considerable expense. NEO published the house layout and plans online.
The Gain in the Details
See a list of the home's features in the Nebraska Energy Office's final report on the project; 10 pp.; May 2005 (PDF 1.3 MB). Download Adobe Reader.
Airtight, Sealed Construction
Perhaps the largest step for the builder, Ken Innes of Skyline Homes in Lincoln, was sealing the home to prevent infiltration of outside air. Controlling this infiltration is a cornerstone of building an energy efficient house. This is because all air that enters the house from outside must be heated in the winter and cooled in the summer. While heating this excess air adds nothing to the comfort of the occupants, it adds significantly to the utility bills.
After discussions with CARB, the builder went to great lengths to seal all openings and around penetrations through the walls and roof. The primary material used to seal is caulk and impermeable wall covering (Tyvek). For example, the builder applied caulk between the top and bottom plates and the walls in order to reduce infiltration. CARB supplied a design detail showing how to tuck the wall covering properly around the window openings and seal them.
Indoor air quality
Once the house is sealed against infiltration of outside air, it becomes necessary to deliver fresh air to the home with fans and to install safety equipment on combustion equipment to prevent back drafting exhaust gases into the house. The builder installed two exhaust fans in the master bathroom and main bathroom that exhaust air out of the house; however the main bathroom fan also provides fresh air from outside.
When construction was complete, CARB tested the ventilation system under different indoor air pressures to make sure it performed as rated. Technicians measured the actual airflow through the exhaust fans under neutral indoor air pressure and under negative pressure (-28 kPa). The negative pressure simulates what happens to the house on a very cold winter morning when the furnace, hot water heater, stove hood, and exhaust fans are operating at the same time. Based on the test results and the recommendations for air quality by the American Society of Heating, Refrigerating, and Air Conditioning Engineers (ASHRAE), the builder set the main bathroom exhaust fan to run 40 minutes of every hour using a remote timer control.
Extra effort for insulation
In addition to air sealing, this prototype is an example of an outstanding job in insulation. Good insulation depends on attention to detail because heat can escape through any forgotten nook and cranny. This house uses R13 rigid insulation at the foundation made of polyisocyanurate, which extends from the bottom of the floor trusses to the foundation floor. All seams are sealed with metal tape. The rim joists are covered with two inches of spray-applied insulating foam (R6.5 per inch). This foam not only insulates, but also seals the rim joists from air infiltration and thus prevents moisture from migrating from the top of the foundation up into the wall cavities.
Homebuilders using typical construction practices in Nebraska install batt insulation against the wall down to the rim joist, which provides a pathway for moisture to form on cold surfaces when air contacts the (usually uninsulated) foundation. Once it forms at the foundation, moisture can migrate up through the batts into the wall cavities, where it reduces insulating value and can cause structural damage.
Finally, the walls are filled with blown-in fiberglass between 2 x 6 in. framing. Based on measurements of performance in the field, CARB believes blown-in insulation fills cavities better than batts and creates fewer "cold spots" where insulation compacts and pulls away from the walls.
Ductwork housed in conditioned plenum in the attic
High-efficiency mechanical equipment
The builder installed an efficient furnace and air conditioner in the prototype home. Most homebuilders install the most inexpensive mechanical equipment they can find for homes in the affordable
In this case, the builder chose an air conditioner with a seasonal energy efficiency ratio (SEER) of 12. The U.S. Department of Energy defines the SEER as the cooling energy delivered to the living space in a home divided by the total energy input in the electricity used to run the cooling equipment. Builders of affordable housing typically choose air conditioners with SEER ratings of 10, so the prototype home has equipment that is 20% more energy efficient for cooling. The refrigerant is free of chlorine compounds that harm the ozone layer in the stratosphere.
For heating, the builder chose a direct-vent, sealed combustion, and condensing gas furnace with an annual fuel utilization efficiency (AFUE) of 93.7%. DOE defines AFUE as the amount of heat delivered to the living space in a home during a year divided by the energy input in the fuel. Nebraska Green Built Homes require a minimum efficiency rating of heating equipment of 90% AFUE.
The mechanical equipment is controlled by a programmable thermostat that allows the homeowner to set the temperature back when an area is unoccupied.
ENERGY STAR rated lighting and appliances
The builder took full advantage of fluorescent lighting and energy efficient appliances throughout the Lincoln prototype home. Lighting can become a significant energy consumer in conventional homes, and incandescent lighting is the most inefficient of all types of lighting fixtures. A typical incandescent light bulb converts less than 10% of the energy in the electricity to light (measured in lumens) and more than 90% to heat. On the other hand, fluorescent light fixtures produce two to four times the lumens output than incandescent lamps from the same amount of electricity.
CARB required that at least 70% of the lighting for the prototype home come from fluorescent fixtures. Nebraska Certified Green Homes require kitchen and bathroom lighting using fluorescent fixtures. The program also prohibits the use of recessed cans in ceilings unless they are sealed to prevent air infiltration. This type of recessed fixture is rated insulated contact (IC). The builder installed several different types of fluorescent fixtures in the bathroom, bedrooms, kitchen, and hallways. And the builder installed compact fluorescent light bulbs in most of the remaining light fixtures, which added up to half of the total light fixtures in the house.
The builder also installed an ENERGY STAR rated dishwasher, which was a minimum requirement of Nebraska Green Built Homes. The homeowner supplies all other appliances.
Advancing Building Science
The testing of this prototype home lead to some interesting lessons learned from pictures taken by the infrared camera. The infrared images show temperature differences that indicate paths of heat loss.
When examining the images, project engineers noticed paths of heat loss at the corners of the framing, where clips hold crossing members together to withstand shocks such as strong winds or small seismic tremors. They are called "hurricane clips," and builders normally place them facing the inside walls because the inside surfaces are easier to reach than those facing outside. Placed on the inside, however, these clips create a path for heat to escape the house because they are made of metal that has high heat conductivity. If instead they were installed on the other side of the framing facing outside, the clips provide no such path for heat loss because they would not be in contact with the conditioned space inside the house.
Insulated window headers
Instead of headers, the builder used clips to secure the tops of the window frames. Then he could fill the space that was previously occupied by the window headers with insulation. The net effect was to reduce lumber requirements and increase the overall energy efficiency of the home. Photos taken with an infrared camera after construction prove there is less heat loss around windows in this prototype home than around windows installed using standard construction techniques.
The Lincoln home demonstrates the concept that quality, energy efficient, environmentally friendly, and affordable housing can be built with little or no extra initial construction costs. In order to do this, the builder must be willing to try new construction techniques.
Launched in the Parade of Homes
Nebraska Governor Dave Heineman introduced the Nebraska Green Built Home prototype for the affordable housing market to the public at a press conference in Lincoln. The home was a part of the Lincoln, Nebraska 2005 Parade of Homes, which showcased Building America and Green Build technologies and ENERGY STAR products. See the governor's May 11 press release.
"This is an important step toward making lower-cost housing more affordable in the long-term for working families," Governor Heineman said. "Buying a certified Nebraska Green Built Home is an assurance that a new home has been built to exacting energy and environmental standards." For background on the project, read an article in the March 2005 edition of the Nebraska Energy Office's newsletter, Nebraska Energy Quarterly.
The Nebraska Energy Office involved the following partners in its prototype energy efficient and affordable home in Lincoln: