When you think of a brand-new home, you likely imagine airtight insulation, the latest energy-efficient appliances, and a glowing EPC (Energy Performance Certificate) rating. But for many homeowners and developers, reality hits hard when their modern build receives a surprisingly mediocre — or even poor — EPC score. This puzzling outcome is known as the EPC paradox. But why does it happen?

1. Assumptions vs. Reality: The Software Limitations

EPC assessments rely heavily on Standard Assessment Procedure (SAP) software, which uses default assumptions rather than on-site performance tests. This means:

  • If your home includes advanced technologies not explicitly listed in SAP, they may be overlooked.

  • Materials like eco-friendly insulation or smart ventilation systems may not be fully recognised.

  • Innovative construction techniques (like SIPs or ICF) can be penalised unless proven through known datasets.

2. Primary Energy vs. Practical Efficiency

The EPC score is often skewed by how energy is generated and delivered:

  • A home using electric heating — even with renewables — can be rated lower due to the primary energy factor applied to electricity.

  • Gas heating, though less environmentally friendly, can score better on an EPC purely due to how the system is weighted.

This creates a frustrating paradox: a more carbon-friendly home may have a lower EPC.

3. Poor Documentation During Assessment

New builds often contain high-end energy features — but if these aren’t properly documented during the EPC assessment, they won’t count. Common issues include:

  • Missing installation certificates for insulation or solar panels.

  • Lack of airtightness test results.

  • No proof of low-energy lighting throughout.

Without evidence, assessors must revert to default (and often worse) values, dragging your rating down.

4. Renewable Energy Not Fully Counted

Some renewable systems — like solar PV, battery storage, or heat pumps — aren’t always fully integrated into SAP calculations. Their real-world impact might be excellent, but their EPC benefit may be modest unless modeled precisely.

5. Overheating Risk Penalisation

To prevent overheating in airtight homes, assessors may apply penalties if your new build lacks sufficient shading, natural ventilation, or solar control. Ironically, a home built to trap heat efficiently can lose points for being too warm in summer.

How to Avoid the EPC Trap in New Builds

If you’re constructing or buying a new property, here’s how to secure the EPC rating your build deserves:

  • Engage a SAP assessor early in the design stage — not just at the end.

  • Provide full documentation for all energy-efficient elements.

  • Consider the EPC implications of your heating system, even if it’s greener in practice.

  • Run pre-EPC simulations to predict and adjust your score.

  • Ensure your builder is familiar with SAP requirements, not just building regulations.

Final Thought: EPCs Don’t Always Reflect Reality

The EPC paradox reveals a critical flaw in how we measure home energy performance. While EPCs serve as an important tool, they sometimes fall short in recognising innovation and real-world efficiency. For homeowners, that means it’s crucial to go beyond the rating — and for the industry, it signals a need for smarter, more nuanced assessment methods.

📍 Final Takeaway

The EPC graph is just the beginning. When you know how to read between the lines, your report becomes more than a score—it becomes a blueprint for saving energy, reducing emissions, and increasing property value.

Ready to unlock the full story of your EPC?
📅 Book your expert EPC assessment today at EPCrate.co.uk.