Ultra-efficient homes: Going beyond an ENERGY STAR® home
Energy-efficient homes that are ENERGY STAR®-certified can offer reduced energy bills, year-round comfort, higher resale value and more. So it’s worth asking whether ENERGY STAR is the most efficient home you can get, or if you could increase the benefits by ramping up the sustainability.
While a home that approaches zero emissions is doable and makes for an excellent abode, ENERGY STAR homes are still likely to represent the best balance of environmental friendliness and practicality.
Let’s take a closer look at the two classes of homes…
What makes a home energy efficient?
According to the Department of Energy (DOE), “While design costs, options, and styles vary, most energy-efficient homes have some basic elements in common: a well-constructed and tightly sealed thermal envelope; controlled ventilation; properly sized, high-efficiency heating and cooling systems; and energy-efficient doors, windows and appliances.”
Learn how builders make a home energy-efficient.
The more these features are incorporated into a home, the more energy efficient it can be, and the better its chances of obtaining an official energy efficiency certification such as ENERGY STAR. Although the ENERGY STAR program uses the Energy Rating Index (ERI) to score home efficiency, the Home Energy Rating System (HERS) Index is more widely recognized and similar to ERI. The lower the HERS score, the more efficient it is, with a score of 100 used as the benchmark.
These indices make it possible for homebuilders to customize and mix-and-match efficiency features in such a way that, even if one area is not particularly efficient, the home can make up for it somewhere else. In the case of ENERGY STAR homes, they must meet or exceed the ERI target that is set through energy modeling of a reference home.
While today’s new homes are significantly more efficient than homes built as little as 20 years ago, there are some signs that improvements in the “average” energy-efficient home have begun to plateau.
In 2015, the average HERS score was 62, according to RESNET, the not-for-profit creator of the index. In 2020, the average HERS score was only a slightly-improved 58, and it remained 58 for both 2021 and 2022. And only one state, California, registered an average score below 40 in 2022.
Next-level efficiency - ultra-efficient homes
Although California, with its average HERS score of 18 in 2022, is closing the gap, most new energy-efficient homes fall short of the realm of ultra-efficiency. The DOE defines ultra-efficient home design as one that uses on-site renewable energy systems to meet the reduced electricity demands of a home built with state-of-the-art, energy-efficient construction practices and features.
Unlike a typical ENERGY STAR home, which can be built in virtually any style and made energy efficient with the right features, an ultra-efficient home is built from the ground up with efficiency in mind. It takes a dedicated approach that incorporates every aspect of the home’s design into the equation.
Early adopters of this innovative style of homes believe the result is a comfortable, bright, and healthy environment. Owners of ultra-efficient homes report enjoying a higher quality of life in their new house. Homebuilders also have good reason to be interested in ultra-efficient homes, as they can receive federal and/or state incentives for building them.
How energy efficient are ultra-efficient homes?
Federal requirements determining what qualifies as ultra-efficient homes are administered by the Zero Energy Ready Homes (ZERH) program. According to the DOE, a ZERH can offset “most or all” of its annual energy usage with a renewable energy system.
Requirements for ZERH certification include:
- being ENERGY STAR-certified
- an ERI value equal to or lower than the ERI of the DOE ZERH Target Home
- indoor air quality certified under EPA Indoor airPLUS
- a parking space equipped with electric vehicle charging
- capable of heat pump water heater and space heater installation
- 100% LED lighting
- 100% of builder-supplied and -installed refrigerators, dishwashers and clothes washers and dryers are ENERGY STAR-qualified
While this may not always result in a zero HERS score, a full-on net zero home does register a zero HERS. In other words, it produces as much energy as it consumes, typically via solar panels, thereby granting its owners the gift of zero electricity bills and strong energy security.
It’s possible for a home to register a negative HERS score if it produces more electricity than it consumes. Such homes are referred to as “positive energy.” Homeowners then have the option to use that extra energy to power electronics around the house, or sell energy back into the grid through a solar buyback or net metering program, if their electricity provider allows it.
Although usually thought of as a commercial and industrial renewable energy source, wind power is technically another possible source of residential power generation for net zero homes. However, the practical difficulties of installing even a small wind turbine in a suburban area–for example, the DOE recommends home electric wind systems only for sites that receive at least 9 mph winds on average annually, and the average system costs $50,000–make wind generation a distant second option in popularity to photovoltaic systems.
How do homes achieve ultra-efficiency?
So now that we’ve considered how ultra-efficient homes negate at least a significant part of the energy they must draw from the grid, let’s look at how they achieve the bulk of their efficiency that carries them above and beyond the average efficient house:
Passive solar design
By installing south-facing windows with highly insulative glass (at least double-pane, Low-E) and a high solar heat gain coefficient, ultra-efficient homebuilders can both light and heat the home using the sun. In fact, the entire south-facing wall is likely to be nearly covered with windows which is termed “glazing.”
Conduction, convection and radiation then store and distribute heat through the home’s thermal mass, which may consist of brick, stone, concrete or tile. The climate determines how much glazing and thermal mass the home needs. Roof overhangs and retractable awnings can also be incorporated to limit heat gain during the hot summer months.
Cool roofs
While south-facing windows are strategically letting in sunshine, the roof of an ultra-efficient home is expelling it, to keep the heat from seeping into the attic and the rest of the home below. It does this by reflecting sunlight and by releasing heat from the house.
These cool roofs come in many different styles and can actually be applied to nearly all types of roof surfaces, from steep to low-sloped. They include:
- terra cotta clay tiles
- membrane/“rubber” roofing
- solar panels
- “cool-colored” traditional roofing materials such as asphalt and polymer shingles, concrete tiles and metal
Landscaping
The yard might not be an aspect you would expect to contribute to energy efficiency, but skillfully done, plants can do quite a bit to help. In the summer they can provide shade from the sun, and in the winter trees planted on the home’s northern side can block chilly breezes that would otherwise necessitate the furnace working harder to keep the home warm.
Alternative home designs
For a truly distinct home design, make your new house an earth-sheltered home. A house like this that’s built either underground or into a berm or hill gains protection against extreme temperatures, as well as volatile weather events such as tornadoes and hailstorms.
Another alternative design option is a straw bale home, in which sustainable, inexpensive straw is used as both insulation and as the primary material in the walls of the house. The builder stacks the bales then seals them with a moisture barrier and outer plaster layer to create a solid foundation. The resultant thick walls have an efficient thermal mass that helps reduce energy use while keeping the home comfortable.
Striking a balance with an ENERGY STAR home
When it comes to ultra-efficient homes, the maxim “All you can do is your best” applies. In many parts of the country, it may be difficult for your family to find a home with a HERS score of less than 20. Current numbers indicate the total number of net zero single-family homes in the U.S. and Canada is around 30,000.
In contrast, more than 2.4 million ENERGY STAR-certified homes and apartments have been built to date, with 9% of new single-family homes built in 2021 receiving certification. Although some states offer more availability than others, ENERGY STAR homes can be found in every state and are an excellent way to make your daily life more sustainable, more comfortable and more affordable in the long run.
- For those in Greater Houston, go here to find a list of builders offering energy-efficient homes in your area.
- Minnesota homeowners can find a map and database with contact info for energy-efficient builders in the state here.
- For other locations, use the DOE’s builder/developer or energy rating company finder here.
