Energy Performance Certificates (EPCs) are designed to offer an objective measure of a property’s energy efficiency. But what happens when two identical homes in the same development receive different EPC ratings?
It’s a scenario that puzzles many homeowners and raises concerns about EPC accuracy and consistency. In this article, we’ll explain why EPC ratings can vary between identical properties, what factors cause these discrepancies, and how to ensure your home receives a fair and accurate EPC assessment.
The Myth of EPC Objectivity: Why Identical Homes Can Get Different Scores
On paper, EPCs are meant to provide a standardised energy efficiency score based on a property’s physical characteristics and energy systems. However, two homes built to the same specifications can—and often do—receive different EPC ratings.
➡️ Need a reliable EPC assessment? Book an EPC survey with EPCrate.
Key Reasons Why EPC Ratings Differ Between Identical Homes
1. Assessment Inputs: Data Entry Variations
EPC assessments rely on assessor inputs into software models. If one assessor records a detail (like loft insulation thickness) based on visible evidence, while another marks it as ‘Unknown’ due to lack of proof, the resulting EPC scores will differ—even if both properties are physically identical.
2. Documentation Availability
One homeowner might provide boiler installation certificates, glazing specifications, and insulation reports, allowing the assessor to input verified, high-performance values. The neighbouring home without this paperwork will see ‘default’ values applied, which are more conservative and can lower the EPC rating by one or more bands.
3. Minor Construction Tolerances
Even in new developments, slight variances in:
Window fitting quality
Airtightness
Insulation installation consistency
can cumulatively impact EPC outcomes. These micro-differences, though negligible to occupants, can affect the modelled energy performance.
4. Heating Controls and Thermostat Settings
If one property has a verified programmable thermostat or heating zone controls visible to the assessor, it gains extra efficiency points. The identical home without such evidence (or where the assessor overlooks them) will lose those points.
5. Lighting and Appliance Choices
Though EPCs don’t account for appliance efficiency, the presence of:
Fixed low-energy lighting (LEDs)
Integrated mechanical ventilation systems
can sway the rating, especially in modern homes. If one home has full LED coverage and another is mixed, ratings may diverge.
The Role of EPC Software Assumptions
EPC software, whether RdSAP (Reduced Data SAP) for existing dwellings or SAP for new builds, fills in gaps with assumptions when information is missing.
Defaults are intentionally conservative, meaning:
Unknown insulation? → Default to uninsulated.
Unknown heating efficiency? → Default to old, inefficient system.
Unknown glazing specs? → Default to single or standard double glazing.
➡️ Learn how ‘Unknown’ entries affect EPCs: Read our deep dive on EPC defaults.
Real-World Example: EPC Discrepancy in Identical Homes
| Property A | Property B |
|---|---|
| Provided cavity wall insulation certs | No documentation available |
| Assessor verified boiler model & SEDBUK | Boiler plate inaccessible |
| Loft hatch accessible for inspection | Loft hatch sealed |
| Installed LED lighting (verified) | Lighting type assumed (defaulted) |
| EPC Band C | EPC Band D |
How to Ensure Your EPC Reflects True Performance
1. Prepare Documentation in Advance
Gather:
Insulation installation records
Heating system manuals & efficiency labels
Glazing specifications
Ventilation system documents
2. Conduct a Pre-Assessment Walkthrough
Walk the property with the assessor to point out:
Heating controls
Loft access points
Hidden retrofits (e.g., floor insulation)
3. Hire Experienced Assessors Who Minimise Defaults
At EPCrate, our assessors are trained to:
Avoid unnecessary ‘Unknown’ defaults
Verify as many property details as possible
Ensure your EPC rating reflects real performance
➡️ Book a detailed EPC survey now.
Why EPCrate?
Transparent Pricing
London-based certified EPC Assessors
Personalised support for documentation and EPC preparation
➡️ Contact EPCrate today.
Conclusion: Identical Homes, Different Ratings—It’s All in the Details
Two identical homes can receive different EPC ratings because of documentation gaps, assessor thoroughness, and software default assumptions. While this may seem like a flaw in the system, it highlights the importance of preparation and hiring skilled assessors who can capture the full efficiency of your property.
Don’t let assumptions cost you valuable EPC points. EPCrate ensures your rating is based on facts—not defaults.
