Are EPC Scores Biased Toward New Builds? A Technical Comparison

When comparing energy efficiency ratings across UK properties, one trend becomes clear: new builds consistently outperform older homes on EPC scores. But is this because they are genuinely more efficient—or is the EPC system itself biased toward newer construction?

In this article, we unpack the technical foundations of EPC assessments and explore whether the scoring system gives unfair advantages to new builds, or whether the differences are justified by design, materials, and regulations.

🧾 Quick Recap: What Is an EPC Score?

An Energy Performance Certificate (EPC) rates how energy efficient a building is, from A (most efficient) to G (least efficient). It’s based on factors such as:

• Heat loss through walls, floors, roof, windows

• Heating system efficiency and controls

• Lighting type and controls

• Renewable energy features

• Ventilation and air tightness

Every UK property sold, rented, or newly built must have a valid EPC.

🏗️ Why Do New Builds Score Better?

Statistically, over 80% of new builds achieve EPC ratings of B or higher, while the majority of older properties fall into the D or E range. This disparity is driven by several technical and regulatory differences:

1. Modern Construction Standards

New homes must comply with Part L of the Building Regulations, which enforce:

• Higher insulation standards (U-values for walls, roofs, windows)

• Reduced thermal bridging

• Air tightness testing and controlled ventilation

• Efficient heating systems (usually condensing boilers or heat pumps)

These features drastically reduce heat loss, which boosts EPC scores.

2. SAP Methodology Favors Design-Efficiency

The Standard Assessment Procedure (SAP) used in EPCs rewards:

• Good insulation and low U-values

• High-performing HVAC systems

• Simple, compact building shapes (less surface area = less heat loss)

New builds are often designed with these in mind, giving them inherent advantages in the scoring system.

3. Built-In Renewables

Many new homes are fitted with:

• Solar panels (PV)

• Mechanical ventilation with heat recovery (MVHR)

• Smart heating controls

These additions earn direct score credits in SAP, further boosting EPC performance.

🧱 What About Older Homes?

Challenges:

Older properties, especially pre-1980s, typically have:

• Solid brick walls (high heat loss)

• Single-glazed or old double-glazed windows

• Less floor/loft insulation

• Inefficient boilers or storage heaters

EPC Limitations for Older Homes:

Even after retrofits, older homes may not score as highly, due to:

• Default assumptions in RdSAP (the reduced version of SAP used for existing homes)

• Inability to assess features not directly visible or documented

• Lack of airtightness testing

🧠 Example: A solid wall that’s been internally insulated may not be credited unless the assessor has clear evidence — even if it performs well in practice.

⚖️ Is This a True Bias or a Reflection of Reality?

✅ EPCs Reflect Performance Potential

New builds are more efficient by design. They simply meet higher standards, use better materials, and often integrate renewables. The high scores are deserved.

❌ But EPC Assessment Tools Aren’t Perfect

RdSAP, used for existing homes, relies on assumptions and defaults. These can under-represent the true performance of upgraded or well-maintained older properties.

⚠️ This creates a perception of bias:

• New builds benefit from measured data and builder documentation

• Older homes are judged partly on standardised guesswork unless upgraded elements are well-documented

🏡 Can Older Homes Compete?

Yes—but it takes effort.

Here’s how to improve an older home’s EPC score:

• Upgrade to a condensing boiler or renewable heating (heat pump)

• Insulate walls, lofts, floors, and pipes

• Replace windows with high-performance glazing

• Install low-energy lighting and heating controls

• Provide documentation for all improvements

• Consider airtightness measures and ventilation systems

💡 Tip: A pre-assessment consultation with an EPC assessor can identify high-impact improvements and help ensure they’re recorded correctly.

📊 Real-World Example: EPC Comparison

Despite substantial upgrades, the older property still scores lower, largely due to architectural limitations and SAP scoring dynamics.

🔍 Key Takeaways

• EPCs aren’t unfair, but the assessment method gives structural and data advantages to new builds.

• The real issue isn’t bias—it’s that older homes are harder to model and improve under current rules.

• Retrofit work must be properly documented to be reflected in EPCs.

• With upcoming legislation requiring rental properties to reach EPC C by 2028, understanding these nuances is crucial for landlords and owners.

Need Help Boosting Your EPC?

At EPCrate.co.uk, we specialise in:

✅ Honest, data-driven EPC assessments
✅ Advice on documenting retrofit upgrades
✅ EPCs for period homes, listed buildings, and conversions
✅ Upgrade strategies tailored to older properties