While Energy Performance Certificates (EPCs) are mandatory for both new and existing buildings, the assessment process and methodology differ significantly. For new-build properties, EPCs are based on design specifications and compliance modeling, while existing buildings are assessed through physical inspections and default assumptions.
In this article, we explain the key differences between EPC assessments for new-builds and existing properties, and how builders, developers, and buyers can ensure accurate and favourable EPC ratings.
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1. New-Build EPCs: SAP Calculations vs Existing-Build RdSAP
| Assessment Type | Methodology | Key Data Inputs |
|---|---|---|
| New-Build EPC | SAP (Standard Assessment Procedure) | Detailed design specs, U-values, air tightness tests, heating system efficiency, renewable integrations. |
| Existing Building EPC | RdSAP (Reduced Data SAP) | Assessor estimates based on visible features, defaults for unconfirmed data (e.g., insulation, heating systems). |
SAP assessments model a new building’s predicted energy performance based on design plans, while RdSAP assessments rely more on physical site observations.
2. The EPC Process for New-Build Properties
Stage 1: Design Stage SAP Calculation — A preliminary EPC is produced to show compliance with Building Regulations Part L.
Stage 2: As-Built SAP Calculation & EPC Registration — After construction, verified specifications and test results (e.g., air tightness) are entered to produce the final EPC.
SAP Calculations are mandatory for:
Newly built homes.
Conversions (e.g., office-to-residential).
Significant extensions (>25% of floor area).
Book your SAP-based EPC assessment now via our Booking Page.
3. Why New-Build EPC Ratings Are Often Higher
New-build properties often achieve EPC Band B or A due to:
Superior insulation and low U-values.
Efficient glazing (double or triple glazed windows).
Air tightness standards (pressure test results influence SAP).
Integration of renewables (solar PV, heat pumps).
Modern heating controls (zoned thermostats, smart systems).
In contrast, existing buildings may struggle to match these efficiencies without significant retrofitting.
4. Documentation Critical for New-Build EPC Success
For an accurate EPC rating, the following documentation is essential:
U-value calculations for walls, floors, roofs.
Window and door specifications.
Boiler/heat pump efficiency ratings.
Air tightness test certificate.
Details of renewable energy installations (if applicable).
Mechanical Ventilation Heat Recovery (MVHR) system details (if installed).
Missing or incomplete documentation can result in default SAP assumptions that lower the EPC score.
5. Common EPC Mistakes in New-Build Projects
| Mistake | EPC Impact |
|---|---|
| Air tightness test results not submitted | Defaults to worst-case infiltration assumptions. |
| Unspecified insulation thickness/details | U-values set conservatively, reducing EPC score. |
| Overlooking heating controls documentation | Loss of efficiency credits in SAP calculation. |
| Missing renewable system certifications | Solar PV or heat pumps not reflected in EPC. |
EPCrate works directly with builders and developers to ensure no energy efficiency feature is missed. Learn more on our About Us page.
6. EPC Recommendations for New-Build Buyers
While new-build homes typically have high EPC ratings, buyers should:
Request a copy of the as-built SAP report.
Verify air tightness test results.
Ensure heating systems and controls match the design specifications.
Understand how renewable energy systems (e.g., solar PV) are contributing to efficiency and bills.
7. EPC Case Study: New-Build Townhouses in London
A development of 12 townhouses in East London achieved EPC Band A ratings by:
Using triple-glazed units with U-values of 0.9 W/m²K.
Installing ASHPs with Seasonal Coefficient of Performance (SCOP) of 3.8.
Achieving an air permeability rate of 3.5 m³/h/m² through rigorous air sealing.
Integrating solar PV systems offsetting 30% of annual electricity consumption.
EPCrate provided end-to-end SAP calculations and EPC registration, ensuring developers received optimal EPC ratings to maximise market appeal.
Conclusion
EPC assessments for new-build properties involve a more detailed and design-driven process compared to existing buildings. Ensuring accurate specifications, air tightness results, and comprehensive documentation is vital for achieving high EPC ratings.
At EPCrate, we specialise in SAP EPC assessments for new-builds, helping developers and homeowners ensure compliance and unlock top-tier energy efficiency ratings. Book your new-build EPC assessment via our Booking Page or contact us through our Contact Page for expert guidance.
