Energy Ratings Ranked by London Borough (2026 EPC Data)
We analysed EPC data across all 33 London boroughs to rank energy performance. The results follow a clear pattern: boroughs with modern housing stock score well, while those dominated by Victorian and Edwardian homes lag behind. Extensions built to current Part L standards can significantly improve your property's energy rating.
TL;DR
EPC ratings across London boroughs are driven primarily by housing stock age. Boroughs with extensive post-2000 development — Tower Hamlets, Newham, Greenwich — have the highest proportion of A-C rated homes. Inner London boroughs with Victorian and Edwardian terraces — Camden, Islington, Hackney, Kensington and Chelsea — have the worst ratings. This matters because extensions built to current building regulations (Part L 2021) act as thermal upgrades: new walls at 0.18 W/m²K and roofs at 0.15 W/m²K dramatically outperform the original fabric of older properties, pulling the whole-house rating upward.
0.18
Wall U-value (Part L 2021)
Building Regulations
0.15
Roof U-value (Part L 2021)
Building Regulations
5-15
SAP points improvement
Estimated from extension
33
London boroughs ranked
DLUHC EPC data
Sources: DLUHC EPC Register, Building Regulations Part L 2021, Mayfair Studio analysis
Best and Worst Rated Boroughs
The pattern is striking. Boroughs that have seen significant new-build development in the last 20 years cluster at the top. Boroughs with predominantly pre-1919 housing stock cluster at the bottom.
| Borough | Estimated A-C % | Dominant stock era | Rating trend |
|---|---|---|---|
| Tower Hamlets | ~55-60% | Post-2000 high-rise | Best in London |
| Newham | ~50-55% | Post-war + regeneration | Strong |
| Barking and Dagenham | ~50-55% | Post-war council + new-build | Strong |
| Greenwich | ~48-52% | Mixed + regeneration | Above average |
| Southwark | ~45-50% | Mixed + new-build | Above average |
| Croydon | ~42-47% | Inter-war + post-war | Average |
| Bexley | ~40-45% | 1930s-1970s suburban | Average |
| Bromley | ~40-45% | 1930s-1960s suburban | Average |
| Ealing | ~38-42% | Mixed Victorian-modern | Below average |
| Wandsworth | ~35-40% | Victorian + some new-build | Below average |
| Lambeth | ~33-38% | Victorian terraces | Poor |
| Hackney | ~30-35% | Victorian terraces | Poor |
| Islington | ~28-33% | Georgian/Victorian | Poor |
| Camden | ~25-30% | Georgian/Victorian | Worst in London |
| Kensington and Chelsea | ~25-30% | Victorian/Georgian townhouses | Worst in London |
Source: Estimated from DLUHC EPC Register data • Data as of Certificates issued to date (analysed March 2026)
Estimated percentages based on EPC certificate data. Not all properties have a current EPC. Actual distributions may differ from certificates on record, as older and lower-rated properties are less likely to have been recently assessed.
Why Housing Stock Age Dominates
Building regulations have progressively tightened thermal performance requirements over the decades. The result is a dramatic difference in fabric performance between eras:
| Element | Pre-1919 | 1930s-1960s | 1990s-2000s | Part L 2021 |
|---|---|---|---|---|
| Walls | ~2.0 W/m²K | ~1.5 W/m²K | ~0.35 W/m²K | 0.18 W/m²K |
| Roof | ~2.3 W/m²K | ~1.5 W/m²K | ~0.25 W/m²K | 0.15 W/m²K |
| Floor | ~1.5 W/m²K | ~1.2 W/m²K | ~0.25 W/m²K | 0.13 W/m²K |
| Windows | ~4.8 W/m²K | ~4.8 W/m²K | ~2.0 W/m²K | 1.2 W/m²K |
Source: Building Regulations historical data and Part L 2021 • Data as of Current standards
A Victorian solid-wall terrace with original single-glazed sash windows has wall U-values roughly 11x worse than current Part L requirements. Even with loft insulation and draught-proofing, the inherent thermal performance of old solid walls limits how far the EPC rating can improve without major intervention.
This is why boroughs like Camden and Islington — with beautiful but thermally poor Georgian and Victorian terraces — consistently show the worst EPC distributions. The buildings are listed or in conservation areas, limiting what can be done to improve them. Meanwhile, Tower Hamlets and Newham have benefited from extensive regeneration, replacing old stock with homes built to modern standards.
How Extensions Improve Your EPC Rating
Extensions are rarely discussed as energy upgrades, but they can have a significant positive impact on your property's EPC rating. Here is why:
- 1.New fabric outperforms old. A rear extension built to Part L 2021 has walls at 0.18 W/m²K and a roof at 0.15 W/m²K. These elements perform 5-10x better than a Victorian solid wall. The extension effectively dilutes the poor performance of the original fabric with high-performance new construction.
- 2.Floor area increases reduce heat loss per m². EPC ratings are calculated per square metre of floor area. Adding well-insulated floor area improves the average. A 20m² rear extension on an 80m² Victorian terrace adds 25% more floor area at dramatically better thermal performance, pulling the whole-house average up.
- 3.Extensions often replace the worst element. In a typical Victorian terrace, the original single-storey rear outrigger is often the worst-performing part of the house — thin walls, poor roof, draughty windows. Replacing it with a modern extension removes the worst thermal element and replaces it with the best.
- 4.Building regulations require whole-house improvements. Part L 2021 requires that when building an extension, you also upgrade certain elements of the existing house (known as “consequential improvements” for larger extensions). This can include upgrading the boiler, adding loft insulation, or improving hot water cylinder insulation.
| Scenario | Before extension | After extension | Change |
|---|---|---|---|
| SAP score | ~45 (E) | ~55-60 (D) | +10-15 points |
| CO₂ emissions | ~6.5 t/year | ~5.8 t/year | -11% |
| Heating cost | ~£1,800/year | ~£1,650/year | -8% |
| EPC band | E | D (borderline C) | One band up |
Source: Mayfair Studio estimate (illustrative) • Data as of Based on Part L 2021 standards
Illustrative example for a 3-bed Victorian mid-terrace (~80m²) with a 20m² single-storey rear extension. Actual improvement depends on existing fabric, heating system, and extension specification.
Part L 2021: What Your Extension Must Achieve
Since June 2022, all new extensions in England must comply with Part L 2021 of the Building Regulations. These are the most demanding thermal performance standards ever applied to domestic construction in England.
| Element | Maximum U-value | Context |
|---|---|---|
| External walls | 0.18 W/m²K | Typically 100-150mm insulation depending on build-up |
| Roof | 0.15 W/m²K | Well-insulated flat or pitched roof |
| Floor | 0.13 W/m²K | Insulated concrete or timber floor |
| Windows/doors | 1.2 W/m²K | Double or triple glazed, thermally broken frames |
| Rooflights | 1.7 W/m²K | Includes roof lanterns and skylights |
Source: Building Regulations Approved Document L1 (2021 edition) • Data as of In force from 15 June 2022
These standards mean that even a small extension adds a thermally excellent shell to your home. The contrast with the existing fabric of a Victorian or Edwardian property is dramatic — and it is this contrast that drives the EPC improvement.
What This Means for Homeowners
EPC ratings are becoming increasingly important for property value, mortgage eligibility, and potential future regulatory requirements. Several practical implications stand out:
- 1.Mortgage lenders are watching EPC ratings. Green mortgage products offer lower rates for properties rated C or above. As the market develops, properties with poor EPC ratings may face higher borrowing costs or reduced mortgage availability.
- 2.Rental properties already face minimum standards. Since 2018, rental properties in England and Wales must have a minimum EPC rating of E. There are ongoing proposals to raise this to C by 2028-2030. Landlords in Victorian-heavy boroughs may find extensions are the most practical route to compliance.
- 3.Extensions offer a dual benefit. Unlike standalone energy retrofit measures (external wall insulation, new boiler, solar panels), an extension both adds living space and improves energy performance. The extension pays for itself through added property value while also reducing energy bills.
- 4.Victorian-heavy boroughs have the most to gain. If you own a Victorian terrace in Camden, Islington, or Hackney with a D or E rating, a well-designed extension could push you to a C — crossing the threshold that increasingly matters for green mortgages and future regulations.
Frequently Asked Questions
Which London borough has the best EPC ratings?
Tower Hamlets, Newham, and Barking and Dagenham tend to have the highest proportion of A-C rated homes, driven by extensive new-build development. Post-2000 high-rise residential construction in these boroughs was built to modern thermal standards.
Which London borough has the worst EPC ratings?
Camden and Kensington and Chelsea tend to have the lowest proportion of A-C rated homes. Both boroughs are dominated by Georgian and Victorian housing stock with solid walls, which are inherently difficult to insulate, particularly when listed or in conservation areas.
Will an extension improve my EPC rating?
Yes, in most cases. Extensions built to Part L 2021 standards (walls 0.18 W/m²K, roof 0.15 W/m²K) perform dramatically better than pre-1919 fabric. A 20m² extension on an 80m² Victorian terrace could improve your SAP score by 5-15 points, potentially pushing you up one EPC band.
What U-values must my extension achieve?
Under Part L 2021 (in force since June 2022): external walls 0.18 W/m²K, roof 0.15 W/m²K, floor 0.13 W/m²K, windows 1.2 W/m²K, and rooflights 1.7 W/m²K. These are minimum standards; many architects specify better performance.
Do I need a new EPC after building an extension?
You are not legally required to get a new EPC after an extension unless you are selling or renting. However, a new EPC after an extension will typically show an improved rating, which can benefit mortgage rates and future sale value. The cost of a new EPC assessment is typically £60-120.