How We Calculate Your Health Score
A transparent, data-driven approach to home energy performance. Every formula, weighting, and data source we use is published where available. Built on open data — assumptions are visible, and the model is still evolving.
Public energy score engine v2.3 · Passport Health Score is the same 0–100 after claim.
- 01Public Estimated Health Score (v2.3): six energy areas — Envelope (30%), Heating (25%), Ventilation (15%), Hot Water (10%), Solar (12%), Storage & Grid (8%).
- 02Not an Energy Performance Certificate — Evolving Home does not issue official EPCs or lodgable assessments.
- 03Smooth 0–100 scoring — every improvement counts; not a replacement for EPC A–G letters.
- 04Built on official EPC data and PVGIS solar estimates where available; estimated when measurements are missing.
- 05Evidence Grade, Flex Potential, and ± range sit beside the score — they are not extra weights of the public 0–100.
- 06The free public score and the Passport Health Score are the same 0–100 energy estimate. After claim, the noun stays Health Score; Evidence Grade stays a sibling letter.
What is a Home Resilience Passport?
Evolving Home helps you decide what you cannot usefully DIY from spreadsheets and an EPC alone: which homes and spends come first when cost and energy sit together. Known vs estimated stays labelled underneath so you do not treat public defaults as a capital plan. Decision support only — not certification, not compliance sign-off. Free score and Passport features run on cloud services with owner control over sharing; offline, on-device storage is a direction, not a present guarantee.
A Home Resilience Passport is a user-owned, privacy-first record of how your home performs, what has been verified, and what should improve next. It is decision support — not a legal certificate, compliance guarantee, or savings promise.
The public Estimated Health Score (0–100) is an energy performance estimate from six fabric and system areas. The free public score and the Passport Health Score are the same 0–100 energy estimate. After claim, the noun stays Health Score; Evidence Grade stays a sibling letter.
Evidence Grade (A–D) and Flex Potential sit beside that score as sibling indicators — input trust and load-shift capability — not extra weights of the public 0–100. Tariff income and programme eligibility are never guaranteed.
Professional review still matters for major fabric, heating, and electrical works. Evolving Home guides sequencing; it does not replace qualified installers, assessors, or retrofit coordinators.
Private export is available for signed-in Passport owners as a beta print-ready summary. Public sharing, partner verification, and collaboration workflows remain under construction.
Last reviewed: 19 July 2026. Passport Health Score v2.3; public score engine v2.3.
Passport Health Score (after claim)
After you claim a home, the Health Score is the same public energy estimate (v2.3). Evidence Grade and coverage facts sit beside it — they are not extra weights of the 0–100. Coverage rows below are file and trust UI — not extra weights of the Health Score.
Energy Performance
the scoreThis is the Health Score — public energy v2.3
Resilience
coverageClimate / exposure facts — not a weight of the 0–100
Verification
coverageConfirmed facts raise trust — not a weight of the 0–100
Improvement Momentum
coverageVerified upgrades over time — not a weight of the 0–100
Sibling indicators (not score weights)
These appear next to scores on public and Passport surfaces. They do not re-weight the public 0–100 energy score.
Evidence Grade
A–DHow complete and trustworthy the inputs are — not a weight inside the public 0–100.
Flex Potential
Low / Medium / HighSeparate capability label for load-shifting potential — not promised grid income.
Score range
heuristicCompleteness-based band around the central estimate — not a statistical confidence interval. Same trust story as Evidence Grade.
EPC letter
A–GOfficial regulated snapshot for context — Evolving Home does not issue EPCs.
Portfolio triage leads with attention bands and EPC context. Property Health Scores are secondary. Attention bands are planning labels — not a separate scoring engine.
Evidence Grade & score ranges
Evidence Grade reflects how complete and trustworthy your inputs are — not a building certification. High completeness may reach Grade B; Grades C–D indicate more estimated facts. On score results you may see ranges such as 67 ± 8 — the margin reflects input gaps, not measured prediction error.
Public Health Score ± margins (product display)
- high confidence → ± 4 score points (Evidence Grade B)
- medium confidence → ± 8 score points (Evidence Grade C) — e.g. 67 ± 8
- low confidence → ± 12 score points (Evidence Grade D)
Single public display source of truth: src/lib/score-uncertainty-display.ts (values above are read from PUBLIC_SCORE_UNCERTAINTY_MARGIN at render time). Engine fields such as uncertaintyPercent are internal completeness metadata and are not a second public ± scale.
Verifying insulation depth, heating system type, and recent energy use narrows the range and improves recommendation quality.
Why archetype matters
Homes are scored against a detected archetype (e.g. residential semi, flat, office). Archetype affects benchmark comparisons, climate-relative rank, and which recommendations are appropriate — a terrace behaves differently from a detached home for fabric-first sequencing.
Illustrative Passport coverage rows
After claim, the Health Score is the same public energy 0–100. Values below are coverage placeholders — not a second overall and not measured certifications. Public free score results show the six-area energy breakdown.
Energy Performance
the score
This is the Health Score — public energy v2.3
Resilience
coverage
Climate / exposure facts — not a weight of the 0–100
Verification
coverage
Confirmed facts raise trust — not a weight of the 0–100
Improvement Momentum
coverage
Verified upgrades over time — not a weight of the 0–100
Why sequencing matters
Evolving Home sequences guidance so you verify uncertain facts first, tackle fabric before major systems, and only then explore flex-ready steps. Oversizing heat pumps or batteries on unverified fabric assumptions wastes capital and can harm comfort.
- Verify First — reduce uncertainty before committing spend.
- Fabric First — cut demand before sizing expensive plant.
- Systems & Storage — professional sizing after fabric is understood.
- Flex Ready — capability only; programme eligibility and income are not guaranteed.
Flex Potential methodology
Flex Potential is an indicative capability screen, not an enrolment result or income forecast. We estimate whether a home may be able to shed load, shift energy, and respond safely without unacceptable comfort risk.
Controllable assets may include heat pumps, batteries, smart controls, EV charging, and thermal storage. Tariff value, VPP eligibility, revenue, and programme availability are not confirmed by the Passport.
Honesty, limitations & professional review
The Health Score is a decision-support estimate, not a certification. The Passport becomes more reliable as evidence improves. Major works should be reviewed by qualified professionals. Regulatory, tariff, incentive, and flexibility-programme details may change and should be checked before decisions are made.
Evolving Home does not replace a retrofit coordinator, engineer, installer, or accredited energy assessor.
- Some mappings remain rule-based and text-driven from EPC fields.
- Confidence margins are completeness-based, not error-calibrated.
- Flex Potential describes capability — programme eligibility and income are not guaranteed.
Planned methodology depth
Future releases will deepen transparency without turning this page into a legal or engineering certification document.
- Published pillar weight formulas and versioned change log
- Calibrated uncertainty from measured prediction error
- Full evidence ladder (documents, bills, photos, pro checks) → Grade A
- Cited research links for flex and thermal-mass claims
- Archetype-specific benchmark distributions from real cohorts
How the Public Score Works (v2.3)
The Health Score is an estimated continuous 0–100 metric that builds on government data like EPC, enriched with public sources where available. It is designed to reward every improvement as your Passport evolves — not to replace a certified EPC assessment.
Unlike static ratings, our score uses continuous curves for smooth progression — no discrete jumps. For example, improving insulation from R-20 to R-30 gradually increases your score based on performance curves.
Continuous Scoring Curves
Metrics like U-values (thermal transmittance) map to scores via smooth curves. Lower U-value = higher score, with diminishing returns at extremes.
COP to Score Mapping
Heat pump COP (Coefficient of Performance) is scored on a curve: ASHP from 3-4.3, GSHP 4+, benchmarked against regional averages.
Weighted Aggregation
Each area gets its own score, then they're combined into your final 0–100 score. Weightings reflect real-world impact on energy use and bills.
6 Component Breakdown
Your score is composed of six weighted components, each fed by multiple data sources for accuracy.
Envelope
Assesses insulation, airtightness, and thermal bridging of walls, roof, floors, and windows.
⚠ U-values are inferred from text descriptions, not measured. This is heuristic, not a full SAP fabric calculation.
Data Sources
- EPC (U-value descriptions → lookup table)
- Airtightness from EPC when present (defaults to ACH50=10)
- SAP 10.2 (benchmark ranges)
- OSM geometry (when available for bridging estimate)
Heating
Evaluates heating system type and efficiency, including boilers, heat pumps, and distribution.
⚠ Rule-based keyword matching from EPC descriptions. Not a full plant simulation.
Data Sources
- EPC (system type, descriptors)
- COP band mapping (ASHP/GSHP)
- Weather compensation / low-flow bonus flags
Ventilation
Measures air quality systems and heat recovery efficiency.
⚠ Rule-based scoring. MVHR efficiency is banded, not measured.
Data Sources
- EPC (vent type field)
- MVHR efficiency band mapping
Water
Analyses hot water heating system type and efficiency.
⚠ Pattern-matched from EPC descriptions.
Data Sources
- EPC (hot water field)
- HPWH / stratified tank / DWHR pattern matching
Solar
Calculates on-site renewable generation based on enriched data and system flags.
⚠ Without a full demand profile, solar utilisation is estimated from defaults. Generation data requires PVGIS enrichment.
Data Sources
- PVGIS (solar irradiance + annual generation)
- EPC (existing PV flag)
- DC coupling / bifacial / tracker flags
Storage / Grid
Evaluates battery storage, grid flexibility, and virtual power plant participation.
⚠ Capability score, not a verified operational optimisation model.
Data Sources
- Battery capacity bands
- VPP participation flag
- TOU optimisation flag
- Thermal storage flag
Our Technology Database
Roughly 80 technologies researched so far across 7 categories. We keep adding as we learn what actually works in real homes.
Envelope and Insulation
35 technologies
Heating and Cooling
45 technologies
Ventilation and Air Quality
20 technologies
Water Heating and Efficiency
15 technologies
Renewables and Solar
25 technologies
Storage and Grid Integration
35 technologies
Smart Controls and Automation
25 technologies
Scoring Curves Explained
Each metric maps to a 0–100 sub-score using smooth curves. Small improvements always count, and gains naturally taper at the high end — just like real-world energy physics.
U-Value → Score (Envelope)
Lower U-values (better insulation) yield higher scores via a sigmoid curve. Example: Wall U-0.18 (R-31) scores ~85, improving to U-0.12 (R-47) reaches 95.
COP → Score (Heating)
Heat pump efficiency on a linear-to-exponential curve. ASHP COP 3.5 scores 70, 4.3 scores 90; GSHP 4+ can exceed 95.
Other Examples
- MVHR recovery: 90% → 80 score, 95% → 95 score
- Battery self-consumption: 30% → 40 score, 60% → 85 score
- Solar yield: Normalized to roof potential via PVGIS
Climate-Relative Rank
Your score report includes a climate-relative rank that compares your home against similar properties in the same climate zone, region, and building type. This is an additive context layer — it does not change your score.
⚠ Important: this comparison is modeled, not empirical
The distributions used for ranking are synthetic — derived from building stock data (UK EPC register, NREL ResStock for US, IS 5281 norms for Israel). They are not computed from real user scores in this system. Ranks are never described as percentiles; they use named tiers to avoid false precision.
How Cohorts Work
Your home is placed in a cohort defined by:
- Climate band — simplified Köppen-Geiger from your coordinates (e.g. temperate, cold, mediterranean)
- Region — UK, US, or IL (distributions differ per country)
- Property type — flat, terrace, semi, detached
- Floor area band — small (<70m²), medium, large, very-large
Example cohort key: temperate:UK:semi:medium
Tiers, Not Percentiles
- LeadingTop ~10% of modeled cohort
- Above averageTop 10–35%
- TypicalMiddle 35–65%
- Below averageBottom 35–65% (15–35th)
- LaggingBottom ~15%
Data confidence: UK = high (EPC register), US = medium (ResStock), IL = low (code norms). Confidence is shown alongside your rank.
Unsupported countries currently return a note asking where you're scoring from so we know which markets to expand next.
Potential Score: Likely vs Stretch
Alongside your estimated Health Score, we show a potential range — what your score could reach with targeted improvements.
Likely
Top 3 high/medium-confidence recommendations applied to your estimated Health Score. Represents a realistic improvement from 2–3 targeted upgrades. Capped at 95.
Stretch
Top 6 feasible recommendations applied (including caveated ones; excludes infeasible). Represents the outer bound if all practical measures are pursued. Capped at 98.
⚠ Potential is bundle simulation, not a certified forecast
Score impact values in our recommendation catalog are manually assigned estimates — not derived from physics calculations or SAP. Interaction effects between co-installed measures are not modelled. Treat the range as directional, not as a savings promise.
Beyond Net Zero: Buildings as Batteries
Our goal is to help every home become better at using, generating, storing, and sharing energy. A score of 100 means a home that is genuinely energy-positive and useful to the grid — not just “net zero” on paper.
A score near 100/100 is archetype-relative: it means a home is close to the strongest practical version of its type, with very low demand, verified generation or storage where relevant, and strong evidence quality. As one illustrative scenario, a highly optimised UK 3-bed semi might generate around 6,000 kWh/year from solar while using roughly 4,000 kWh, creating a net export of about -2,000 kWh/year. That is not the universal definition of the 90–100 band.
Thermal Mass as Storage
Buildings can store energy as heat in walls, floors, and thermal mass. Hedar, A. S.; Zatti, M.; Bovera, F. (2023), “Buildings as Batteries — Unlocking Grid Flexibility from Smart Management of Domestic Heating,” Proceedings of the 2023 International Conference on Clean Electrical Power, ICCEP, pp. 192–200, supports the idea that smart heating control can unlock domestic flexibility. Our score treats this as indicative capability, not measured performance.
Heat Pumps for Load Shifting
A heat pump paired with a well-insulated building envelope is a controllable thermal load. Power-to-Heat during surplus renewable periods stores energy in the building fabric itself. On Octopus Agile or similar dynamic tariffs, a smart ASHP can run predominantly on cheap overnight electricity, shifting kilowatt-hours from grid-stress periods to off-peak abundance.
Solar + Battery + V2G
Rooftop solar generates. A home battery (10–20 kWh) stores and time-shifts. Vehicle-to-Grid (V2G) may add 40–80 kWh of EV battery into the equation. Together, these could help a home ride through grid stress — but actual export income depends on tariffs, programmes, and equipment. We describe this as indicative Flex Potential, not promised earnings.
Every Home as a VPP Node
A single prosumer home is interesting; many consented homes could eventually support demand response or VPP-style programmes. Evolving Home tracks estimated contribution potential only. We do not confirm programme eligibility, dispatch, or revenue.
What Score 100 Actually Means
(UK 3-bed semi)
vs 4,000 kWh consumed
prosumer asset
Research basis: Hedar, A. S.; Zatti, M.; Bovera, F. (2023). "Buildings as Batteries — Unlocking Grid Flexibility from Smart Management of Domestic Heating." Proceedings of the 2023 International Conference on Clean Electrical Power, ICCEP, pp. 192–200. Heat pump Power-to-Heat concepts are illustrative — not a guarantee of grid payments, savings, or programme eligibility.
What is heuristic vs live vs planned
Live (actively used in scoring)
- EPC fabric descriptions → U-value lookup → component score
- EPC system type fields → rule-based component scores
- Airtightness from EPC when present
- PVGIS solar generation when enriched
- Storage/grid capability flags (battery, VPP, TOU)
- Climate-relative rank (v2.3, modeled distributions)
Heuristic (in use, but approximate)
- U-value inference from EPC text (not measured)
- COP scoring from qualitative descriptors
- Thermal bridging default junction count
- Potential score impact values (manually assigned)
- Confidence / uncertainty (completeness-based, not error-calibrated)
- Climate rank distributions (synthetic, not from real user scores)
Planned (not yet in core scoring)
- Smart meter time-series calibration
- Full OSM geometry coupling in every score
- Thermal-camera / retrofit proof ingestion
- Calibrated uncertainty from real measured error
- Public contribution pipeline for model updates
Known limitations (current model)
- Some component mappings are still rule-based and text-driven.
- Confidence and uncertainty are estimated from input completeness, not measured calibration error.
- Validation dataset includes both measured and benchmark archetypes; measured sample is still small.
How we test accuracy
Your indicative Health Score uses a published, versioned model. Before research or scoring changes reach homeowners, we run automated checks and require human review for major methodology updates — we do not silently rewrite how your score works.
Our Open Methodology Commitment
We believe energy scoring should be auditable — not a black box. Where something is estimated rather than measured, we say so plainly on this page and in your Passport.