Why Sub-45 HERS Scores Are Exceptionally Difficult Without Zero-Energy Techniques
In recent years, some builders have begun advertising HERS scores in the 30s as if they are routine outcomes of “better building practices.” While these claims can sound compelling, they warrant careful context—particularly when they are presented as averages across production homes without renewable energy or zero-energy strategies.
At Two Structures Homes, we build high-performance, energy-efficient homes and verify every one through independent third-party testing. Our lowest confirmed HERS score to date is 45. We employ the same construction techniques commonly cited in discussions of sub-40 performance. That hands-on experience provides a grounded perspective on what is realistically achievable—and where meaningful technical challenges begin.
What a HERS Score Actually Measures
The Home Energy Rating System (HERS) Index, maintained by the Residential Energy Services Network (RESNET), compares a home’s modeled energy use to a reference home built to 2006 energy-code standards.
- HERS 100 = reference home
- HERS 55 = already very efficient by national standards
- HERS 45 = approximately 55% more efficient than the reference home
- HERS 37 = approximately 63% more efficient
For context, RESNET reports that the average HERS score for homes that were independently tested and HERS-rated in 2023 was approximately 57. This figure reflects only the subset of new homes that underwent third-party HERS verification—not all new homes built nationwide. Even within this tested population, scores in the 30s remain well outside the norm.
Why the 30s Are a Different Category Entirely
It is important to understand that the HERS scale is not linear. The difference between a HERS 55 and a HERS 37 is not incremental—it is exponential. Each point lower requires disproportionately greater precision, tighter tolerances, and more aggressive strategies.
Once a home approaches the mid-40s, traditional “code-plus” construction methods begin to plateau. Further reductions demand a level of execution that pushes the limits of conventional residential construction.
What It Typically Takes to Reach ~37 HERS Without Renewables
To approach a HERS score in the high-30s without solar, geothermal, or other zero-energy inputs, a home must operate near the limits of standard residential practice. This typically requires all of the following, executed with exceptional consistency:
1. An Exceptionally Tight Building Envelope
- Advanced air-sealing approaching Passive-House-level detailing
- Minimal thermal bridging
- Very high insulation values, often spray-foam or hybrid assemblies
- Blower-door results that are consistently exceptional—not merely good
2. High-Performance Windows and Doors
- Triple-pane or near-Passive-House window packages
- Very low U-factors with climate-specific solar heat-gain tuning
3. Precisely Designed Mechanical Systems
- Fully engineered Manual J, S, and D calculations
- Minimal duct losses
- Thorough commissioning
4. Ultra-Efficient Domestic Hot Water
- Heat-pump water heaters or advanced tankless systems
- Extremely short plumbing runs with minimal recirculation losses
5. Very Low Plug and Lighting Loads
- Aggressive assumptions about appliance use and occupant behavior
- High-efficiency appliances modeled at best-case usage
Even with all of these measures in place, achieving mid-30 HERS scores consistently across multiple homes without renewables remains uncommon.
How Very Low HERS Scores Are Commonly Achieved
Across the industry, homes that report sub-40 HERS scores often incorporate one or more of the following factors:
Modeled vs. As-Built Ratings
Early energy models frequently assume ideal execution. Final blower-door-tested results can be higher once real-world construction variables are introduced.
Highly Repetitive Plans
Repetition can reduce variability—but only when execution is tightly controlled and continuously monitored.
Alternative Structural Systems
Systems such as insulated concrete forms (ICFs) or structural insulated panels (SIPs) inherently reduce heat loss compared to conventional framing.
Renewable Energy Credits
Solar photovoltaic systems and other on-site generation can credit energy production back into the HERS calculation, significantly lowering the final score—even when the home’s intrinsic envelope and systems are similar to others.
This distinction matters because a net HERS score is not the same as intrinsic building performance.
Verified Performance vs. Marketing Language
The only authoritative measure of energy performance is a final HERS certification issued by an independent rater, including blower-door testing and completed as-built documentation.
As emphasized throughout building-science literature and trade publications, energy-efficiency claims are most meaningful when supported by third-party verification—not promotional language. This distinction is important for buyers, lenders, and appraisers alike.
Why HERS Exists
The HERS Index did not originate as a builder-led initiative. It emerged in the early 1980s from the mortgage and financial industries, which sought a reliable way to quantify utility savings for underwriting decisions. That effort eventually led to RESNET and today’s standardized rating system—built around objectivity and independent verification.
What Buyers Should Take Away
- HERS scores in the 30s are real—but rare
- Achieving them without renewables requires exceptional construction and near-perfect execution
- Many advertised scores rely on modeling assumptions, credits, or energy offsets
- The only number that truly matters is the final, certified HERS score
- A verified HERS 45 already represents elite performance in today’s market
Our Position at Two Structures Homes
We are proud of our homes and confident in our data. We remain committed to:
- Testing every home
- Publishing real, verified results
- Focusing on durable, measurable performance—not theoretical projections
Energy efficiency should be proven, not promised.
Availability of Public HERS Data
While RESNET publishes annual reports showing how many homes are HERS-rated in each state and the average HERS score by state, it does not publicly release score distributions by threshold (such as how many homes scored below HERS 40 or HERS 45 in Oklahoma). That level of detail exists only within RESNET’s internal National Buildings Registry or through custom data requests.
As a result, there is no official, publicly available figure quantifying how many Oklahoma homes have achieved sub-40 HERS scores. Any discussion of very low HERS performance must therefore rely on verified individual certifications or builder-reported case studies rather than statewide statistical confirmation.
How to Evaluate Claims of Exceptional HERS Performance
A HERS score below 50 represents very high energy performance. That does not make it impossible—but it does make it important for buyers to understand how the score was achieved and verified. These questions help consumers compare claims accurately.
- Is the HERS score final and certified, or modeled?
- Was the home tested by an independent third-party rater?
- Does the score include solar or other energy offsets?
- Is this score typical, or a best-case example?
- What was the blower-door test result (ACH50)?
- How were mechanical systems designed and commissioned?
- Were alternative construction systems used?
- Are modeling assumptions realistic for everyday living?
- Can I see the actual HERS certificate?
- How does this compare to typical new homes?
Why These Questions Matter
A HERS score is a powerful tool—but only when it is:
- Verified
- Clearly explained
- Presented with appropriate context
Asking these questions does not challenge a builder’s integrity. It helps consumers understand what the number truly represents and whether it aligns with their priorities.
Just like fuel-economy ratings on vehicles, HERS scores are most useful when you understand the testing conditions behind them.