A systematic translational mapping comparing smart readiness indicator (SRI) and BACS standard (EN ISO 52120-1) under EPBD 2024 recast

Aims and objectives

The relationship between the SRI and BACS standard has gained growing scholarly attention, producing several partial comparisons that this paper consolidates and extends. Walczyk & Ożadowicz (2025) provide the most comprehensive narrative review to date but remain descriptive, without dissecting aggregation logic or attempting scoring-framework translation. Ożadowicz (2022) proposes a hybrid BACS-SRI design framework through SWOT analysis, identifying complementarities without service-level mapping. The SRI2MARKET project, an EU Horizon 2020 initiative piloting the Smart Readiness Indicator in real buildings across several Member States, provides some initial comparative insights. Its Deliverable D2.4 (Cleto et al., 2024) offers a service-to-function overlap table identifying approximately 74% topical overlap but addresses domain coverage rather than the structural comparison of scoring methodologies and classification outputs. On the empirical side, Garzia et al. (2024) found no correlation between SRI scores and energy performance across 59 buildings; Person et al. (2025) demonstrated that measured savings deviate significantly from both SRI-predicted efficiencies and EN ISO 52120-1 forecast factors; and Van Thillo, Verbeke, and Audenaert (2022) concluded that the BAC factor method does not reliably estimate achievable energy savings.

The present study is further situated within the rapidly expanding SRI literature. Delavar et al. (2025) provide a comprehensive review of the field, while a growing body of work approaches framework interoperability from the digital building model perspective: Calandri et al. (2025) demonstrate a BIM-based data-exchange framework for automating SRI calculation, illustrating the shared data infrastructure that the EPBD digital building logbook (Article 16) is intended to support. (Martinez et al., 2025) develop and implement a standardised SRI on-site audit procedure, which directly informs the integrated site-visit protocol proposed in this paper. A complementary procedural-integration strand examines how SRI assessment can be combined with statutory building inspections under the recast EPBD (Melero et al., 2026).

This research compares the EU’s two smart building assessment frameworks: the SRI and the EN ISO 52120-1:2022. In the absence of a formal translational mechanism between them within the shared legislative framework of the EPBD recast, measurement theory (Stevens, 1946) and multi-criteria decision analysis are adopted to compare their scoring systems across nine analytical dimensions: assessment paradigm, domain coverage, functional granularity, scoring scale, aggregation logic, classification structure, weighting approach, translation feasibility, and policy applicability, and to develop a translational mapping between the two frameworks.

The novelty lies in formally characterising these differences and translating them into actionable solutions through systematic comparison, service-level translational mapping, and an integrated assessment protocol for the 2026–2027 EPBD implementation period. The study is organised around three core objectives:

1. To systematically compare the scoring framework of the SRI and EN ISO 52120-1:2022.

2. To develop a systematic translational mapping of more granular SRI functionality levels to EN ISO 52120-1:2022 efficiency classes.

3. To assess policy implications and identify pathways for regulatory convergence.

Multi-criteria qualitative catalogue in the SRI

The SRI was developed through EU-funded technical support studies (Verbeke et al., 2020) and formalised in Commission Delegated Regulation (EU) 2020/2155 (EU, 2020a) and Implementing Regulation (EU) 2020/2156 (EU, 2020b). SRI was designed as an informative tool to measure a building’s capacity to use information and communication technologies for adapting its operation to occupant needs, grid requirements, and energy efficiency objectives (EU, 2020a). SRI employs a bottom-up multi-criteria framework organised across four hierarchical layers aggregated through a six-step weighted summation.

Calculation methodology and weighting

The SRI score is derived through a six-step bottom-up aggregation (Ma et al., 2023; Verbeke et al., 2020), as shown in Figure 1:

1. Service-level assessment: applicable services are triaged; each is assigned a functionality level (FL 0–4), yielding ordinal impact scores (I_s,ic(FL)) for the seven impact criteria from the lookup table (EU, 2020a; Verbeke et al., 2020).

2. Domain-level aggregation: services are equally weighted within each technical domain (d) to produce domain impact scores (I_d,ic).

3. Impact criterion normalisation: domain scores are weighted by building-type and climate-zone factors (W_d,ic) and normalised to percentages of theoretical maxima (Equation (1)), generating a 9 × 7 diagnostic matrix.

   1

   ${\mathit{\text{SR}}}_{\mathit{\text{ic}}}=\left[{\Sigma }_d{W}_{d,\mathrm{ic}}·I_{\mathit{\text{d,ic}}}\right]/\left[{\Sigma }_d{W}_{\mathit{\text{d,ic}}}·I_{\mathit{\text{max(d,ic)}}}\right]\times 100$

4. Key functionality aggregation: the seven criteria are grouped into three EPBD-mandated functionalities (energy performance, occupant needs, and energy flexibility), with equal weighting of relevant criteria within each.

5. Total score: the three key functionalities are equally weighted (33.3% each) to yield a final percentage (0–100%).

6. Class mapping: the percentage is converted to an A–G rating (e.g., A: 90–100%; G: <20%).

Figure 1

Domain weighting factors follow three rules: for energy-related criteria (IC1, IC2, IC7), weights derive from building energy balance profiles across five climate zones, with MC fixed at 20% and DE and EV at 5% each (Ma et al., 2023); for occupant-related criteria (IC3–IC6), equal weights apply across applicable domains; and within key functionalities, weights default to equal but may be nationally adapted. Member State discretion in weights, triage rules, and domain applicability may introduce cross-national fragmentation (Verbeke et al., 2020). While residential and non-residential buildings use different methods and weighting tables, service definitions and functionality levels remain consistent across typologies.

Two operational features of the SRI methodology are central to its national implementation. First, a triage process governs how non-applicable services are handled: assessors identify services that are absent or not relevant to a given building and exclude them prior to normalisation, so that scores reflect only applicable capabilities (Ma et al., 2023; Verbeke et al., 2020). Second, the framework is explicitly adaptable to local conditions, default weighting factors, service catalogues, and triage rules may be modified by Member States and regional authorities through the SRI platform to reflect national building stock, climate, and policy priorities (Ma et al., 2023). This flexibility, together with the guidance issued under the EPBD support package, is intended to promote consistent application, but it also permits cross-national divergence that a formal translation between SRI and BACS would help to contain.

Quantitative factor-based method in EN ISO 52120-1:2022

EN ISO 52120-1 establishes the normative framework for assessing the contribution of building automation, controls, and systems/technical building management (BACS/TBM) to building energy performance. Published by CEN (European Committee for Standardisation) in March 2022 as the European adoption of ISO 52120-1:2021, it replaces EN 15232-1:2017 (EN ISO 52120-1, 2022). The EPBD defines BACS as products, software, and engineering services facilitating energy-efficient, economical, and safe operation of technical building systems through automatic controls and manual management facilitation (EPBD, 2024). Article 13 mandates that non-residential buildings with an effective rated output for heating, air-conditioning, or combined ventilation systems exceeding 290 kW be equipped with BACS possessing specific capabilities (i.e., continuous energy monitoring, efficiency benchmarking, and interoperable communication) by the 31^st December 2024, extending to building systems exceeding 70 kW by the 31^st December 2029.

Convergence of frameworks

The two frameworks share substantial common ground, reflecting the SRI service catalogue’s foundation derivation from the EN 15232 function lists that preceded EN ISO 52120-1. The SRI2MARKET Deliverable D2.4 (Cleto et al., 2024, Table 5) systematically mapped SRI services against BACS and TBM function categories and identified substantial overlap across heating, cooling, DHW, ventilation, and lighting. Walczyk & Ożadowicz (2025) confirm that six of the SRI’s nine domains are also addressed in the BACS standard. Both frameworks employ functionality or control levels progressing from manual to advanced automated control; both differentiate residential from non-residential buildings; and both are co-referenced under the EPBD 2024 recast (EPBD, 2024). Furthermore, the EU.BAC (2024) compliance verification checklist maps the four BACS capabilities mandated by EPBD Article 13(10) to BACS standard functions, significantly overlapping with the SRI’s monitoring and control domain.

Divergence of frameworks

The SRI and EN ISO 52120-1:2022 differ fundamentally in scope and purpose. The SRI measures smartness as a multi-dimensional capability, evaluating energy, comfort, health, convenience, information, and grid flexibility through seven impact criteria (Verbeke et al., 2020). In contrast, the BACS standard is a single-criterion engineering tool focused solely on energy performance (EN ISO 52120-1, 2022). Five of the SRI’s impact criteria therefore lie completely outside the EN ISO standard’s boundary.

Their methodological paradigms are equally incompatible. The SRI relies on a checklist approach: assessors assign ordinal functionality levels based on installed technology, producing scores independent of actual energy use. Whereas the EN ISO 52120-1:2022 standard applies ratio-scale efficiency factors directly to building-specific calculations. As Stevens (1946) demonstrated, direct numerical mapping between ordinal and ratio scales is mathematically invalid without empirical bridging data.

The frameworks’ contrasting aggregation logics, that is the SRI’s compensatory weighting versus the BACS standard’s weakest-link rule (see the comparative analysis above), create misaligned incentives. The SRI may reward low-cost upgrades, while the ISO standard encourages fixing the weakest element first.

Additionally, there is asymmetry in domain coverage. The SRI contains three standalone domains (electricity, EV charging, and dynamic envelope) with no direct EN ISO equivalent, representing 24% of its Method B services. Conversely, the EN ISO standard covers additional detail in areas such as humidity control.

Therefore, a systematic translation between the two frameworks is urgently required. Pilot evidence from Pascual & Boneta (2024) shows that even perfect BACS Class A compliance yields only moderate SRI ratings, approximately 43% (SRI Class E) across 172 pilot assessments, leaving building owners facing investment uncertainty and double-assessment risks during the 2026–2027 transposition.

Heating domain mapping

Heating is the main demonstration case. Table 2 shows that it has the highest match between the two frameworks. Seven of the ten heating services in the Method B catalogue map directly to EN ISO 52120-1 heating functions 1.1 to 1.9. Those seven services are H-1a, H-1b, H-1c, H-1d, H-2a, H-2b and H-2d. The other three map only in part. Thermal energy storage (H-1f) maps to function 1.10. The class definitions for 1.10 do not include grid-responsive charging, which is the highest functionality level of H-1f. Performance reporting (H-3) maps to the generic technical building management reporting function 7.4. Flexibility and grid interaction (H-4) maps to smart grid integration function 7.7. Function 7.7 is credited only at management level and has no heating efficiency class. No heating service is therefore entirely without an EN ISO counterpart.

All service-level mappings in this study come from the detailed Method B catalogue in the SRI v4.5 assessment package (Ma et al., 2023). That catalogue has 54 non-residential services. Method A is the simplified 27-service subset of the same catalogue. Every Method A service is also a Method B service, so the mapping has no Method A-only entries. In the heating domain, service H-1c is “Control of distribution fluid temperature (supply or return; a similar function applies to direct electric heating networks)”. It maps directly to EN ISO 52120-1 function 1.3 (Control of distribution network temperature). The two share the same control levels, that is no control, outside-temperature-compensated, and demand-based. Grid-oriented thermal storage and load shifting is placed in two other services. Service H-1f (Thermal Energy Storage for heating) maps its charging control to ISO function 1.10. Its highest functionality level is grid-responsive demand-side management, which goes beyond the standard. Service H-4 (Flexibility and grid interaction) maps only to the management-level smart grid integration function 7.7. It therefore earns no heating efficiency-class credit. Table 3 uses the SRI v4.5 catalogue structure exactly. The domain counts are: heating 10, domestic hot water 5, cooling 10, ventilation 6, lighting 2, dynamic envelope 3, electricity 7, EV charging 3, and monitoring and control 8. That is 54 services in total.

Directly mapped functions show clear semantic correspondence, with SRI FL 0–3 broadly aligning to BACS Classes D–A. However, the alignment is not mathematically equivalent: SRI evaluates seven impact criteria independently of measured energy use, whereas EN ISO 52120-1 uses precise efficiency multipliers. The highest SRI tier (FL 4) exceeds the EN ISO 52120-1 scope, creating a one-sided translation limit whereby top-tier BACS Class A can reach only approximately SRI FL 3.

Cross-domain mapping

Table 3 summarises the domain-level feasibility of translating SRI Method B services to EN ISO 52120-1 disciplines. Across all domains, 30 of 54 services (56%) map directly, 17 services (31%) map partially, and 7 services (13%) have no corresponding EN ISO function. The domains with high translation feasibility (heating, domestic hot water, cooling, ventilation, and lighting) align closely with conventional building automation functions historically defined in EN 15232 and retained in the BACS standard. In these areas most SRI services correspond directly to existing BACS control functions, reflecting the shared technical foundation of HVAC and lighting automation.

In contrast, weaker alignment occurs in domains associated with newer smart-building and energy-management functions. Partial or absent mappings are concentrated in electricity services (six partially mapped to Technical Building Management, TBM), monitoring and control (six of nine services only partially represented in TBM), and dynamic envelope technologies, where EN ISO covers automated blinds but not broader façade systems such as smart glazing. The EV charging domain has no equivalent representation, making it entirely unmapped within the BACS standard.

These results indicate that translation feasibility is strongly linked to the historical scope of BACS standards. Traditional HVAC and lighting controls show strong structural correspondence, whereas emerging domains related to electrification, advanced monitoring, and adaptive building envelopes fall outside the current ISO functional framework. Consequently, any translational mapping between the two systems remains inherently partial and domain-dependent.

This domain-level asymmetry implies that full BACS compliance (even at Class A) remains necessary but insufficient to achieve high SRI ratings, as several critical SRI domains receive no credit under the BACS framework alone.

Empirical calibration against pilot evidence

To calibrate the normative mapping against field evidence, the results are anchored to the SRI2MARKET pilot benchmarks (Cleto et al., 2024; Pascual & Boneta, 2024). Across 172 assessments in seven EU Member States, buildings certified at the highest BACS efficiency class (Class A) achieved an average SRI score of only approximately 43%, corresponding to SRI Class E. This quantifies the structural asymmetry established qualitatively above: because 44% of SRI services map only partially or not at all to EN ISO 52120-1 functions, and because five of the seven SRI impact criteria fall outside the standard’s energy-only boundary, full BACS Class A compliance is necessary but not sufficient for a high SRI rating. The SRI2MARKET digital assessment tool operationalises this relationship by explicitly linking SRI functionality levels to BACS efficiency classes for the overlapping HVAC and lighting services, providing empirical support for the translational mapping proposed here while confirming that the SRI’s broader, non-energy domains cannot be inferred from BACS classification alone. This calibrated benchmark is carried forward into the policy analysis where it motivates the recommendation to adopt EN ISO 52120-1 Class B as the minimum compliance threshold for overlapping HVAC and lighting services, since even full Class A compliance does not guarantee a high SRI rating.

Regulatory timeline asymmetry

The 2024 EPBD recast introduces an asymmetric regulatory timeline, mandating BACS standards years before the SRI for identical building segments. Under Article 13(9), non-residential buildings exceeding 290 kW must install BACS by December 2024, extending to those over 70 kW by December 2029 (EPBD, 2024). Conversely, Article 15(2) mandates SRI assessments for the 290 kW threshold until June 2027 (EPBD, 2024). This creates a legislative gap, as Member States must transpose these provisions into national law by May 2026, one month before the Commission’s official SRI testing report is even published in June 2026. Table 4 outlines this asymmetrical regulatory timeline.

Figure 4

Significant investment risks are created for building owners by this regulatory asymmetry. Capital investments for the December 2024 BACS mandate must be made without future SRI ratings being known. Because a significant portion of SRI services have no or only partial counterparts in the BACS standard, compliance with even top-tier BACS Class A provides no guarantee of high SRI ratings. Through this structural asymmetry, it is demonstrated that critical smart-ready domains are left unaddressed by BACS compliance alone, whereby stranded assets are risked.

Furthermore, significant pressure is placed upon Member States by this disjointed timeline. These regulations are required to be transposed into national law by May 2026, a month before the official SRI testing report is published. Without formal guidance being provided, there is a high risk of fragmented national implementations, by which the EPBD’s standardisation goals are undermined.

Double assessment burden and the integrated protocol

Once the Article 15 delegated act is implemented, dual verification of BACS compliance and SRI assessment will be required for buildings exceeding 290 kW (EPBD, 2024). To unify these currently independent methodologies, an integrated site-visit protocol is proposed, building on standardised SRI on-site audit procedures (Martinez et al., 2025; Melero et al., 2026). This protocol was formulated by comparative mapping, allowing SRI evaluation, BACS class determination, and EPC data collection to be combined into a single workflow.

This proposed protocol is designed across five phases, which are as follows:

1. Pre-visit preparation including method selection and BACS documentation review.

2. A building walkthrough where SRI functionality and EN ISO control levels are simultaneously assessed employing translational mapping.

3. Concurrent scoring facilitated by direct translation mapping for applicable services between SRI FL and EN ISO 52120-1 CL.

4. EPC integration, where the BACS class determines BAC efficiency factors (f_BAC,H; f_BAC,C; f_BAC,DHW; f_BAC,el) for input into EN ISO 52000-1 calculations.

5. Post-visit reporting, including digital logbook uploads, eliminates duplicated site visits while preserving both assessment outputs, the SRI score (0–100%, Class A–G) and BACS Class (A–D) remain distinct but co-produced from a single evidence base.

To minimise future SRI rating risk (where top BACS Class A may still yield only moderate SRI scores) building owners cannot rely solely on BACS compliance. SRI-exclusive domains (EV charging, smart electricity management, dynamic envelopes) default to baseline without supplementary measures. Targeted supplementary investments in these domains are therefore required to bridge the energy-focused BACS framework and SRI’s broader multi-criteria scope ahead of mandatory 2027 assessments.

Performance measurement gaps

A fundamental limitation is shared by both the SRI and BACS frameworks: neither is sufficiently connected to measured operational performance.

On the SRI side, the indicator evaluates technology presence, not operational effectiveness. Garzia et al. (2024) found no correlation between SRI scores and energy performance class across 59 buildings. Person et al. (2025) conducted the first empirical field validation, finding that EN ISO 52120-1 forecast factors predicted 26% savings for advanced functionality levels, but a district heating system achieved only 16.8%, while a heat pump achieved 51.3%, demonstrating that identically weighted SRI services yield drastically different real-world outcomes.

On the BACS standard side, Van Thillo, Verbeke, and Audenaert (2022) concluded that the BAC factor method does not reliably estimate achievable energy savings, as fixed factors cannot account for building design, occupant behaviour, or climate context. Vandenbogaerde et al. (2023) quantified this variability, finding actual savings ranging from 7 to 37% for heating emission control, ranges far wider than fixed factors represent.

A critical “carbon-blindness” (absence of operational carbon metrics) is exhibited by both systems; operational greenhouse gas emissions are entirely ignored, despite explicit EPBD mandates. Moreover, energy flexibility is contradicted: while grid-interactive performance is comprehensively covered by the SRI, actual flexibility cannot be quantified by its qualitative ordinal scoring system. Meanwhile, there is no scope to evaluate the flexibility in the quantitative EN ISO standard. Therefore, real operational effectiveness remains comprehensively unmeasured by either tool.

Recommendations for framework convergence

Five policy recommendations are proposed for the 2026–2027 EPBD transposition window.

1. Formalisation of translational mapping between SRI and EN ISO 52120-1 as an official technical report proposed under CEN/EN ISO that systematically defines the interaction and translation rules for its implementation to prevent national regulatory fragmentation.

2. Establishing EN ISO 52120-1 Class B as the minimum compliance threshold for overlapping services, ensuring that building owners are granted investment confidence regarding baseline HVAC and lighting infrastructure.

3. Mitigation strategies for the double assessment burden by piloting an integrated site-visit protocol, through which SRI evaluation, BACS classification, and EPC data are seamlessly combined into a single operational workflow.

4. Systematically introducing a dynamic carbon weighting layer into both assessment frameworks, enabling time-varying grid emission factors to be accurately captured. For the SRI, weighting IC1 and IC7 by marginal emissions displaced by demand response; and for the BACS standard, extending the BAC factor method to include carbon-weighted factors (f_BAC,CO2) capturing the carbon value of automation beyond energy quantity reduction.

5. Operationalising measurement-based SRI Method C using real-time metered data calibrated against EN ISO BACS predictions, ensuring that the expected energy and carbon reductions are rigorously empirically validated.

Limitations

The analysis of EN ISO 52120-1:2022 relies on publicly available descriptions and published Annex A factor values rather than an exhaustive clause-by-clause review of the copyrighted standard (EN ISO 52120-1, 2022). The proposed translational mapping remains empirically unvalidated, necessitating further calibration. The study presents no new empirical data, the contribution is methodological, not experimental. Moreover, the findings are bounded by the early 2026 regulatory landscape, which could be altered by impending legislative updates.