EPC Ratings Explained: A Developer's Guide to Energy Performance Certificates

What is an EPC?

An Energy Performance Certificate (EPC) rates the energy efficiency of a building on a scale from A (most efficient) to G (least efficient). Every property in England and Wales must have a valid EPC when built, sold, or rented. Scotland and Northern Ireland have similar but separate schemes.

EPCs were introduced in 2007 as part of the EU Energy Performance of Buildings Directive. Since then, over 25 million certificates have been lodged — creating one of the richest open datasets about UK housing stock.

The two scores: current vs potential

Each EPC contains two energy efficiency scores on a scale of 1-100:

• Current energy efficiency — what the property scores right now, based on its construction, insulation, heating system, and glazing.
• Potential energy efficiency — what it could score if recommended improvements were made (e.g., cavity wall insulation, solar panels, boiler upgrade).

The numeric scores map to letter bands:

The average UK property scores around D (60-65). The government's target is for all homes to reach Band C by 2035.

What data is in an EPC?

Beyond the headline rating, each EPC contains rich property data:

• Floor area — total internal floor area in square metres
• Construction age band — when the property was built (e.g., "1900-1929")
• Property type — house, flat, bungalow, maisonette, park home
• Wall type and insulation — cavity wall, solid wall, insulated or not
• Roof type and insulation — pitched, flat, loft insulation thickness
• Heating system — boiler type, fuel, controls, hot water system
• Windows — single, double, or triple glazed
• Lighting — proportion of low-energy lighting
• Environmental impact — CO₂ emissions in tonnes per year
• Recommendations — suggested improvements with estimated cost and savings

Accessing EPC data programmatically

The official EPC register is available at epc.opendatacommunities.org, but it's cumbersome for production use — rate-limited, requires manual registration, and returns raw CSV.

With the Homedata EPC API, you can look up any property's EPC data by UPRN in a single call:

curl "https://homedata.co.uk/api/epc-checker/100022612238/" \
  -H "Authorization: Api-Key YOUR_API_KEY"

Response:

{
  "uprn": 100022612238,
  "current_energy_efficiency": 72,
  "potential_energy_efficiency": 85,
  "last_epc_date": "2023-05-15",
  "epc_floor_area": 65.0,
  "construction_age_band": "1967-1975",
  "epc_id": "0000-0000-0000-0000-0000"
}

The API returns 7 fields from the EPC register. The numeric scores (current_energy_efficiency, potential_energy_efficiency) are the key values — use the band table above to convert them to letter ratings (e.g., 72 → Band C).

Minimum EPC requirements for landlords

Since April 2020, all rental properties in England and Wales must have a minimum EPC rating of Band E. Landlords who let properties rated F or G face fines of up to £5,000.

The government has proposed raising this to Band C by 2028 for new tenancies (though this has been delayed). This makes EPC data critical for:

• Letting agents — flagging non-compliant properties before they're listed
• Portfolio managers — identifying properties that need improvement investment
• Mortgage lenders — assessing green mortgage eligibility
• PropTech platforms — building energy efficiency features into property search

Use cases for EPC data

Portfolio compliance screening

If you manage a portfolio of rental properties, you can batch-check EPC compliance:

import requests

API_KEY = "your_api_key"
portfolio_uprns = [100022612238, 10090067699, 200003553960]

for uprn in portfolio_uprns:
    resp = requests.get(
        f"https://homedata.co.uk/api/epc-checker/{uprn}/",
        headers={"Authorization": f"Api-Key {API_KEY}"}
    )
    epc = resp.json()
    score = epc.get("current_energy_efficiency", 0)

    # Derive letter band from numeric score
    if score >= 92:   band = "A"
    elif score >= 81: band = "B"
    elif score >= 69: band = "C"
    elif score >= 55: band = "D"
    elif score >= 39: band = "E"
    elif score >= 21: band = "F"
    else:             band = "G"

    if score < 39:  # Band F or G
        print(f"⚠️  UPRN {uprn}: Band {band} ({score}) — NON-COMPLIANT")
    else:
        print(f"✅ UPRN {uprn}: Band {band} ({score})")

Green mortgage assessment

Combine EPC data with the Solar Assessment API to model green upgrade potential — estimated savings, payback periods, and post-improvement EPC scores.

Getting started

Start looking up EPC data in minutes:

1. Create a free Homedata account
2. Get your API key from the developer dashboard
3. Try it: GET /api/epc-checker/{uprn}/

See the full EPC API reference for all available fields and query options.