Article 10: Time to Retire ECG-19? Updating Office Benchmarks With Evidence From 6,000 Greater London Buildings

A series mining the PhD thesis "London and UK Office Buildings: Investigating Energy Use and Landlord-Tenant Influences" (Azhari, 2025).

Key takeaway. The UK mainstream office energy benchmarks (ECG-19 and CIBSE TM46) are based on a 1992 study. The Greater London empirical data shows actual offices nowhere near those benchmark values. A refresh is overdue.

Chart

Benchmarks and empirical reality, standard air-conditioned office (illustrative)

Mainstream UK office benchmarks rest on a 1992 study. REEB and the Greater London empirical median sit far below ECG-19 typical and CIBSE TM46.

A benchmark older than the smartphone

The UK office energy benchmark that underpins the Display Energy Certificate scheme and most consulting practice has its roots in a 1992 study. That study became the Energy Consumption Guide 19 (ECG-19), published by Action Energy in 2003 and adopted as the basis for CIBSE TM46 in 2008.

ECG-19 defines four office typologies (naturally ventilated cellular, naturally ventilated open-plan, standard air-conditioned, prestige air-conditioned) with typical and good-practice values for electricity and gas energy use intensity (EUI). TM46 carries these forward. DECs use them as the comparator for the operational rating displayed in the lobby of every public-sector building above the size threshold.

The benchmarks are the most-cited reference points for office energy in the UK. They are also a generation out of date. Building stock, building services, occupancy patterns and the carbon intensity of grid electricity have all changed materially in the thirty-plus years since the underlying data was collected. The Greater London empirical data in this thesis provides a basis for an evidence-led refresh.

What the empirical data shows

For the 6,038 office Self-Contained Units in Greater London with metered data for 2017, the median EUIs sit at materially different levels from the ECG-19 typical values. The direction is mixed. Some categories have improved (lighting and heating efficiencies are higher than they were in 1992). Others have worsened (electricity loads have grown with plug-in IT, mechanical ventilation, longer hours and more cooling). The net result is that the benchmark values do not reliably describe the modern office stock.

The Better Buildings Partnership Real Estate Environmental Benchmark (REEB) is closer to the empirical reality than ECG-19 or TM46. REEB is based on the BBP member portfolios, which tilt toward larger and better-managed assets, so its values are not directly substitutable for a population benchmark, but they are within striking distance.

The Greater London 6,038-office dataset offers a denser, broader and more recent empirical base than either ECG-19 or REEB. Used carefully, it could underpin a refresh of TM46 that combines the BBP private-sector experience with the public-sector evidence behind DEC.

The 2026 National Buildings Database (DESNZ), which the author contributed to, has since provided national-scale median EUIs by office activity group. General Office sits at 103 kWh per square metre per annum. Business Units at 64. Studios at 47. Office (Local Authority and Central Government) at 126. Film Studios and Computer Centres at 131. These are direct empirical inputs for a refreshed TM46. They also reveal a spread that the single ECG-19 office typology cannot capture: nearly a threefold difference in median EUI across the five groups. Any benchmark refresh that does not separate them is mixing buildings with materially different energy profiles into a single average.

What a refresh would have to do

A credible refresh of the office benchmarks would have to make four moves.

First, define the office typology in 2025 terms. The four ECG-19 typologies were sensible in 1992. They are less so now. Mixed-use offices, high-rise serviced offices, build-to-rent flexible workspace, biotech and research-and-development offices, and post-COVID hybrid offices each have distinct energy profiles that the 1992 typology was not designed to capture. Article 5 argued that height above six storeys and post-1980 construction are meaningful inflection points. Both should feed into any new typology.

Second, separate electricity and gas explicitly. The 1992 benchmark conflated total energy in some contexts. Modern stock and modern policy require a clean separation between electricity (which is the larger and more variable component) and gas (which is the heat-decarbonisation policy lever).

Third, build the benchmark from a clean stock-level dataset. The 6,038-office Greater London sample is one candidate. The BBP REEB portfolio is another. A combined sample, with appropriate weighting, would give national coverage and stratification by typology, age and tenancy.

Fourth, design the benchmark to be refreshed regularly. The 1992-to-2025 gap is not a feature; it is a failure mode. A modern benchmark methodology should specify the cadence and method of refresh from the start, so the next gap is years rather than decades.

Why the benchmarks matter

It might be tempting to treat the benchmark question as a technical detail of the building-services world. It is more consequential than that.

Benchmarks anchor expectations. They are the reference point against which every operational rating is compared, every DEC is interpreted, every good practice claim is calibrated. A benchmark that no longer reflects reality lets average buildings claim to be above good practice and undersells the achievement of buildings that are genuinely performing well.

Benchmarks anchor policy. Any operational rating scheme that uses a size threshold (see Article 1 for the 1,000 square metre case) needs benchmarks calibrated to the population it actually covers. Without modern benchmarks, the policy infrastructure rests on weak foundations.

Benchmarks anchor capital decisions. Asset managers, lenders and investors use benchmarks to compare assets and to set capex priorities. A miscalibrated benchmark systematically misallocates capital across the stock.

The TM46 refresh is therefore a public-good investment, on a par with maintaining national accounts or census infrastructure. It deserves to be treated as such.

Who should lead the refresh

The natural sponsor is CIBSE, which owns the TM46 publication. The natural partner is the BBP, which has the REEB dataset and the industry credibility. The natural data provider is BEIS (now DESNZ), which holds the meter data and the access agreements. The thesis suggests that academic and consulting capacity in the UK is sufficient to do the work. The constraint is governance and funding.

The pattern is familiar. The Australian NABERS scheme (Article 9) succeeded in part because the equivalent benchmarks were refreshed regularly within a stable governance model. The UK does not need to invent the model. It needs to apply it to TM46.

What the data does not see

The empirical data is Greater London only, while ECG-19 and TM46 are intended for the whole UK. Direct substitution should be done carefully. The 2017 snapshot pre-dates significant electrification and post-COVID operating-pattern changes, so any refresh based on it is a baseline rather than a future projection. Office activity classification (standalone, multi-tenant, mixed-use) requires heuristics that other research teams may apply differently. Energy meter coverage is not complete; premises without metered data are absent from the EUI distributions used in the comparison. Updating a benchmark is a governance act as much as an analytical one. The article makes the analytical case but does not deliver the consensus process.

The next article picks up that London-versus-rest-of-UK question directly. Article 11 examines how far the Greater London empirical findings can be generalised to England and Wales, and where they break down.

Limitations

The empirical data is Greater London only, while ECG-19 and TM46 are intended for the whole UK; direct substitution should be done carefully. The 2017 snapshot pre-dates significant electrification and post-COVID operating-pattern changes, so any refresh based on it is a baseline rather than a future projection. Office activity classification (standalone, multi-tenant, mixed-use) requires heuristics that other research teams may apply differently. Energy meter coverage is not complete. Premises without metered data are absent from the EUI distributions used in the comparison. Updating a benchmark is a governance act as much as an analytical one. The article makes the analytical case but does not deliver the consensus process.

References

• Azhari, R. (2025) London and UK Office Buildings Investigating energy use and landlord/tenant influences. Doctoral thesis (Ph.D), UCL (University College London). URL: https://discovery.ucl.ac.uk/id/eprint/10204821/

• Action Energy (2003). Energy Consumption Guide 19 (ECG-19): energy use in offices.

• CIBSE (2008). TM46: Energy Benchmarks. Chartered Institution of Building Services Engineers. Available at: https://www.cibse.org/knowledge-research/knowledge-portal/tm46-energy-benchmarks

• Bordass, B., and Field, J. (2007). Energy benchmarks for non-domestic buildings.

• Hong, S. M., and Steadman, P. (2013). Developing benchmarks for office buildings.

• Better Buildings Partnership (2020). Real Estate Environmental Benchmark: 2019 energy snapshot. Available at: https://www.betterbuildingspartnership.co.uk/our-priorities/measuring-reporting/real-estate-environmental-benchmark

• Bruhns, H., Jones, P., Cohen, R., and colleagues (2011). CIBSE Guide F: Energy Efficiency in Buildings. Available at: https://www.cibse.org/knowledge-research/knowledge-portal/guide-f-energy-efficiency-in-buildings

• Evans, S., Fennell, P., Humphrey, D., Liddiard, R., Oraiopoulos, A., Palmer, J., Ruyssevelt, P., Shamsi, H., Amrith, S., and Steadman, P. (2026). National Buildings Database Phase 2. Department for Energy Security and Net Zero. Available at: https://www.gov.uk/government/publications/national-buildings-database-phase-2-understanding-great-britains-buildings

Read next

• Article 2: Why EPCs Do Not Tell You How Much Energy a Building Uses.

• Article 9: NABERS for Britain.

About this series

This article is part of a fifteen-piece series adapting the 2025 PhD thesis "London and UK Office Buildings: Investigating Energy Use and Landlord-Tenant Influences" (Azhari, 2025) for a mixed academic and industry readership. The empirical findings draw on the 3DStock model of 6,038 office Self-Contained Units in Greater London with metered energy data for 2017, supplied by BEIS under a data-sharing agreement, alongside the Better Buildings Partnership Real Estate Environmental Benchmark. The qualitative findings draw on semi-structured interviews with seven major UK property organisations, conducted during the 2021 lockdown. Interviewees and their organisations are anonymised by role and organisation type. Please cite the original thesis for academic use.

Author. Rayan Azhari completed his PhD at the UCL Bartlett School of Environment, Energy and Resources in 2025, supervised by Paul Ruyssevelt and Kathryn Janda. The research was supported by the EPSRC Centre for Doctoral Training in Energy Demand (LoLo) and UK Research and Innovation through the Centre for Research into Energy Demand Solutions.

Other articles in the series. Article 1 The 30/85/89 Problem; Article 2 Why EPCs Do Not Tell You How Much Energy a Building Uses; Article 3 Eighteen Per Cent; Article 4 Mapping the Stock; Article 5 Height, Age and the Fuel Question; Article 6 The Split-Incentive Problem; Article 7 Green Leases and Service Charges; Article 8 From 38 to 73 Per Cent Energy Savings; Article 9 NABERS for Britain; Article 10 Time to Retire ECG-19; Article 11 Can London Speak for England and Wales; Article 12 The Hybrid-Work Footprint; Article 13 Why I Used Linear Regression Over Random Forest; Article 14 Vertical Postcodes; Article 15 What Is a Building?