Methodology

Data source

EPC2C uses data from the MHCLG Open Data Communities EPC Register API — the official government database of lodged Energy Performance Certificates for England and Wales. This is the same data underpinning the government’s Find an energy certificate service.

When you search a postcode, EPC2C queries this register and returns the most recent lodged EPC for each property at that postcode. The data includes:

• Current EPC band and SAP score
• Potential EPC band (if all recommended measures are installed)
• Construction details: property type, construction era, wall type, heating system
• Recommended improvement measures from the lodged EPC
• Indicative costs from the lodged EPC (where available)

The accuracy of this data depends on when the EPC was lodged and the assessor who conducted it. Older EPCs may not reflect the current state of the property.

Confidence levels

EPC2C uses a four-level confidence system to indicate the reliability of estimates:

How band uplift is estimated

EPC band uplift projections in the Compliance Plan are based on a simplified SAP sequential subtraction methodology.

Each measure has an estimated SAP point contribution derived from:

• The improvement’s SAP points recorded in the lodged EPC (where available from the EPC register)
• GoGreen Alliance’s experience of typical SAP uplift for each measure type by property era and construction type

SAP points are converted to EPC bands using the standard Government conversion table:

EPC Band	SAP Score Range
G	1–20
F	21–38
E	39–54
D	55–68
C	69–80
B	81–91
A	92+

Measures are applied sequentially: the projected SAP score is calculated by adding the uplift from each selected measure to the current SAP score. Interactions between measures (e.g. a heat pump requiring better insulation to perform optimally) are not fully modelled at Medium confidence. The Verified Survey tier accounts for these interactions.

How costs are calculated

At Medium confidence (Compliance Plan), cost ranges are derived from:

• Indicative costs from the lodged EPC register record (where present)
• GoGreen Alliance’s published m² rates for each measure type, based on West Midlands installation experience
• Standard property size assumptions by construction era and type

These are presented as a range (e.g. £400–£800) reflecting typical contractor variation. Actual quotes may fall outside this range depending on access, scaffolding requirements, and local market conditions.

At High confidence (Verified Survey), costs are calculated from actual measured dimensions extracted from the RdSAP XML file uploaded by the DEA after site visit. This produces GoGreen Alliance’s specific m² rate applied to the actual wall area, roof area, and floor area of the property — producing estimates typically accurate to ±15%.

GoGreen Alliance m² rates

GoGreen Alliance’s cost rates are based on real West Midlands installation pricing as of 2024–2025. They are reviewed periodically but may not reflect current market conditions in all regions of England and Wales. Properties in London, remote rural areas, or with unusual access requirements will typically see higher costs.

Why not a certified RdSAP calculation

A certified RdSAP (Reduced Data Standard Assessment Procedure) calculation requires a qualified DEA to:

• Physically inspect and measure the property
• Collect over 100 data points about the property’s construction and services
• Enter data into accredited software
• Lodge the certificate on the national register

EPC2C cannot replicate this process. The Compliance Plan uses EPC register data and cost rules to produce planning-level estimates — suitable for deciding whether to commission works, which measures to prioritise, and whether an exemption is likely. It is not suitable as evidence of compliance.

When to get a verified survey

We recommend upgrading to a Verified Compliance Survey (Tier 3) when:

• You need cost estimates accurate enough to obtain formal contractor quotes
• The compliance plan suggests a borderline outcome (e.g. projected EPC C with a narrow margin)
• You are considering a MEES exemption that requires professional evidence
• The lodged EPC is more than 5 years old or predates significant works
• The property has solid walls, unusual construction, or listed status
• You need to demonstrate due diligence to a mortgage lender or auditor

Limitations

EPC2C is a planning tool. Results should be understood in the context of the following limitations:

• EPC register data quality varies by assessor and date of assessment
• Measure interactions are simplified at Medium confidence
• Cost estimates are West Midlands-based and may not reflect your local market
• Band uplift estimates assume standard installation quality and conditions
• The tool does not account for planning constraints, listed building restrictions, or lease conditions without DEA input

For questions about the methodology, contact hello@epc2c.co.uk.