Homeowners are often confused when two neighbouring or near-identical properties receive very different Energy Performance Certificate (EPC) ratings. Same layout, same size, same street—yet one scores a solid Band C, while the other struggles at Band E.
This discrepancy isn’t a mistake. EPC ratings are influenced by specific, measurable energy-efficiency factors, not appearance, comfort, or age alone. Understanding these differences is crucial for sellers, buyers, and landlords looking to protect property value or improve compliance.
Our experienced EPC Assessors in London regularly explain these variations during assessments:
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1. EPC Ratings Are Evidence-Based, Not Visual
One of the biggest misconceptions is that EPCs are based on how a home looks or feels. In reality, EPCs rely on:
Verified insulation levels
Heating system efficiency
Heating controls and zoning
Glazing type and performance
Documented energy improvements
Two homes may look identical, but if one has documented upgrades and the other doesn’t, their EPC scores will differ—sometimes significantly.
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2. Insulation Differences (Even When You Can’t See Them)
Insulation is one of the highest-weighted EPC factors.
Common differences between similar homes:
One loft insulated to modern depth, the other partially or inadequately
One cavity wall insulated, the other left empty
Pipe and hot water cylinder insulation present in one home only
Even small insulation gaps can cost valuable EPC points. If insulation can’t be verified or accessed, assessors must assume lower default values.
3. Heating Systems and Controls Make a Huge Difference
Heating efficiency is another major EPC differentiator.
Two similar homes may differ because:
One has a modern condensing boiler, the other an older model
One uses smart thermostats and programmers, the other manual controls
One has TRVs fitted to radiators, the other doesn’t
Even if both homes are warm, EPCs reward efficient control, not comfort.
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4. Glazing Isn’t Always Equal
Windows often appear identical but perform very differently in EPC calculations.
Key differences include:
Early double glazing vs modern energy-rated glazing
Secondary glazing installed in one home only
Draught-proofing present in one property but not the other
A single poorly performing window or door can lower a home’s overall thermal efficiency score.
5. Lighting and Electrical Efficiency
Lighting is a smaller EPC component, but it still matters—especially when scores are close.
Differences include:
One home fully fitted with LED lighting
The other still using halogen or incandescent bulbs
Fixed external lighting not energy efficient
When EPC scores sit near a band threshold, lighting alone can tip the result up or down.
6. Renewable Energy Installations
One of the clearest EPC differentiators is renewable energy.
Examples:
One home has solar PV panels
One uses solar hot water
One integrates energy monitoring or battery storage
Even modest renewable installations can add significant EPC points, pushing a property into a higher band.
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7. Documentation and Proof of Upgrades
Two homes may have the same upgrades—but only one has proof.
EPC assessments depend on:
Visible insulation
Manufacturer specifications
Installation certificates
Receipts or guarantees
Without documentation, assessors must apply standard assumptions, which often penalise the score. This is one of the most common reasons similar homes receive different ratings.
8. Extensions, Alterations, and Layout Changes
Even subtle structural changes can affect EPC results.
Examples include:
A rear extension with poor insulation
Converted lofts with inconsistent thermal performance
Open-plan layouts increasing heat loss
Added rooms with inefficient heating
Two homes may have started identical but evolved differently over time.
9. Maintenance and System Condition
EPCs also reflect system performance, not just presence.
Differences arise when:
One boiler is serviced and efficient
Another is operational but poorly maintained
Radiators are balanced in one home but not the other
Maintenance issues may not be obvious to owners but can affect EPC calculations.
10. Assessment Timing and Preparation
Finally, preparation plays a major role.
One homeowner may:
Replace bulbs with LEDs
Gather documentation
Top up insulation
Address draughts
The other may book an EPC without preparation, leading to a lower score—despite similar property potential.
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How to Align Your EPC with Your Home’s True Potential
If your home scores lower than a similar property nearby, it doesn’t mean yours is inefficient—it often means untapped EPC potential.
Steps to Take
Review your existing EPC report
Identify gaps in insulation and controls
Gather evidence of past upgrades
Make low-cost, high-impact improvements
Book a reassessment only when ready
Many properties can gain one or two EPC bands with targeted improvements alone.
Conclusion
Two similar homes can have very different EPC ratings because EPCs measure evidence-backed energy performance, not appearance or comfort.
Key Reasons for EPC Differences
Insulation depth and visibility
Heating efficiency and controls
Window and door performance
Lighting efficiency
Renewable energy presence
Documentation quality
Maintenance and preparation
Understanding these factors empowers homeowners and sellers to close the EPC gap, improve compliance, and protect property value.
Email :info@epcrate.co.uk
Phone:020 34884142
