At first glance, it doesn’t make sense: two homes on the same street, built at the same time, with the same layout—and yet they receive different EPC (Energy Performance Certificate) ratings. How can that happen? Let’s take a forensic look at the hidden variables behind EPC scoring, and why “identical” homes often aren’t identical in the eyes of assessors.

🔍 1. The EPC Isn’t About the Home—It’s About the Evidence

EPC assessments are data-driven, but that data is often based on what can be seen or proven. If one homeowner provides documentation—like a certificate for upgraded insulation or proof of a condensing boiler—and the other doesn’t, their scores will differ, even if the actual performance is the same.

Example:

  • Home A provides proof of wall insulation and gets a Band C.

  • Home B has the same insulation but no paperwork, so defaults are used, dropping the rating to Band D.

🧱 2. Assumptions vs Reality: The Role of Defaults

When assessors can’t verify an element of the property (like floor insulation, roof materials, or double glazing specs), they use default values based on the property’s age and type. These defaults are often less favourable and can significantly affect the SAP score.

Identical design ≠ Identical assumptions.

If one assessor sees a modern control system for heating, and the other doesn’t mention it, that alone could shift the EPC score.

📸 3. The Importance of Visual Access and Detail

Sometimes, differences come down to what’s visible or accessible during the visit:

  • Blocked access to lofts = assumed lack of insulation

  • No label on a boiler = older default efficiency applied

  • Curtain or cupboard hiding a thermostat = control system not counted

Minor observational differences add up, especially in a system with multiple inputs and weightings.

💡 4. Lighting, Controls & Extras Make a Difference

Even seemingly minor features can sway the rating:

  • One home has 100% low-energy lighting, the other 60%

  • One has a smart thermostat and TRVs (thermostatic radiator valves), the other doesn’t

  • One uses a modern hot water cylinder, while the other’s is uninsulated

These may seem small, but together they can push a property from Band D to Band C or higher.

🏗️ 5. Renovations, Retrofits & Overlooked Upgrades

Post-build changes such as loft insulation, solar PV installations, or upgraded doors/windows can dramatically impact EPC scores—but only if they are seen or documented.

Two homes might have followed different maintenance paths since construction. EPC doesn’t care about the blueprint; it cares about the present condition and efficiency features.

🛠️ 6. Assessor Judgement, Software, and Human Variability

Even though EPCs use standardised software, assessors still:

  • Select options from dropdowns that require judgement

  • Interpret ambiguous features (e.g. wall types, ventilation)

  • Input dimensions, photos, and evidence differently

No two assessors are identical, and neither are their evaluations.

🧮 Final Thought: EPCs Are as Much About Process as Property

When one house gets a Band C and the next-door twin gets a D, it’s rarely a mistake—it’s usually a difference in documentation, detail, or defaults.

✅ At EPCrate.co.uk, We Make Sure You Don’t Miss Out

We ensure:

  • Your upgrades are counted

  • Evidence is collected and properly logged

  • You get clear advice on raising your EPC rating cost-effectively

Identical homes deserve identical scores—if the right story is told.

🔎 Book a certified EPC assessor today at EPCrate.co.uk and let us help you uncover your property’s real potential.

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