Technical Summary
UK Residential Automated Valuation Model
1. Model Overview
The Gadsden Valuations AVM produces point estimates of residential property market value for properties in England and Wales, consistent with the IVS 104 definition of Market Value.
For each property, the model produces:
- A point estimate of market value (£) with upper and lower bounds
- A confidence tier (1–3, or declined) with Forecast Standard Deviation mapped to the EAA common 0–7 scale
- Comparable transactions supporting the estimate
- Downloadable PDF report with full audit trail
1.1 Intended Use Cases
The AVM is designed for integration into lender valuation cascades. It operates as the first node in an AVM → desktop → physical inspection workflow, providing structured outputs with per-property confidence scoring. It is not intended as a standalone replacement for physical valuation where required by lender policy or regulation.
- Portfolio revaluation for Basel 3.1 compliance (expected January 2027)
- Remortgage AVM-assisted valuations where physical inspection is not proportionate
- Independent cross-check against physical valuations or competing AVM outputs
- Desktop review support for valuers conducting restricted-service assessments
- Market monitoring for the 10% revaluation threshold
1.2 Coverage
England and Wales. Four standard residential property types: detached, semi-detached, terraced, and flats/maisonettes. The model does not cover Scotland, Northern Ireland, commercial property, new-build prior to first sale, or non-standard constructions.
2. Methodology
Gradient-boosted decision tree ensemble trained on Land Registry data enriched with government open data sources.
2.1 Validation Approach
All accuracy metrics use strict quarterly bulk test: the model is trained on transactions up to a cutoff date and tested exclusively on future transactions it has never seen. The current test set comprises 147,188 properties from the Q4-2025 bulk test. This prevents data leakage and ensures published figures reflect real-world predictive performance.
2.2 Benchmark Methodology
All accuracy metrics are measured against Land Registry completion prices — the actual amount paid in arm’s-length transactions. This is a materially harder test than benchmarking against surveyor opinion (which is itself an estimate with a ±5–10% margin against eventual sale prices).
The industry leader, Hometrack, reports ~80% PE10 benchmarked against surveyor valuations. A like-for-like comparison against actual sale prices would produce lower figures. Published PE10 figures from providers using the surveyor benchmark are not directly comparable with our figures.
3. Accuracy Metrics
| Metric | Value | Industry Context |
|---|---|---|
| Median Absolute % Error (MdAPE) | 6.0% | Single digits considered strong (Ecker 2020) |
| Within ±5% (PE5) | 43.3% | |
| Within ±10% (PE10) | 69.4% | Key lender evaluation metric |
| Within ±15% (PE15) | 82.7% | |
| Within ±20% (PE20) | 89.4% | |
| Median absolute error | £17,250 | |
| Test set size | 147,188 | Q4-2025 bulk test |
3.1 By Property Type
| Type | MdAPE | PE10 | PE15 | PE20 | N |
|---|---|---|---|---|---|
| Flat | 7.2% | 63% | 77% | 85% | 23,817 |
| Terraced | 5.9% | 69% | 82% | 89% | 47,321 |
| Semi-Detached | 5.6% | 72% | 85% | 91% | 43,907 |
| Detached | 6.0% | 70% | 84% | 91% | 32,143 |
3.2 By Price Band
| Price Band | MdAPE | PE10 | N |
|---|---|---|---|
| <£150k | 9.3% | 53% | 21,652 |
| £150-300k | 5.6% | 72% | 59,783 |
| £300-500k | 5.3% | 75% | 43,719 |
| £500k-1M | 6.3% | 69% | 20,176 |
| £1M+ | 10.0% | 50% | 1,858 |
4. Confidence Model
Each valuation receives a confidence tier based on data availability and comparability factors. This satisfies the IVS 105 requirement for accuracy measures and the EAA ESSVM requirement for a per-property confidence score translatable to Forecast Standard Deviation.
| Tier | Confidence | Typical Profile | Recommended Action |
|---|---|---|---|
| 1 (High) | EAA 0–2 | Dense comparables, known floor area, common type | Accept for valuer review |
| 2 (Medium) | EAA 3–4 | Some comparables, partial data, less common type | Desktop review recommended |
| 3 (Low) | EAA 5–6 | Sparse comparables, missing key data, unusual property | Physical inspection required |
| Declined | EAA 7 | Insufficient data for meaningful valuation | Cannot value |
Confidence can be upgraded by the client. The most impactful upgrade is provision of an EPC (£60–120), which supplies floor area, construction age, and energy characteristics — typically sufficient to move a property from Tier 2 to Tier 1. This creates a practical path to maximise high-confidence coverage without sacrificing accuracy.
5. Known Limitations
The model values properties based on recorded data. It cannot account for:
-
•
Internal condition — renovation status, kitchen/bathroom quality, structural issues. This is the primary limitation of any AVM and the principal reason physical inspection remains necessary for higher-risk lending decisions.
-
•
Bespoke improvements — extensions or conversions not yet reflected in EPC or planning data
-
•
Legal encumbrances — restrictive covenants, rights of way, leasehold complications beyond Land Registry data
-
•
Micro-location — specific view, aspect, noise, or neighbourhood factors a local agent would consider
-
•
Market lag — Land Registry data lags completion by 2–4 months
The confidence model flags properties where unobserved factors are more likely to affect accuracy.
6. Data Sources
| Source | Update Frequency | Licence |
|---|---|---|
| HM Land Registry Price Paid | Monthly | OGL v3 |
| EPC Register | Monthly | OGL v3 |
| ONS Census 2021 | Decennial | OGL v3 |
| ONS House Price Index | Monthly | OGL v3 |
| GIAS School Register | Daily | OGL v3 |
| Ofsted Inspection Ratings | Rolling | OGL v3 |
| Environment Agency | Annual | OGL v3 |
All data sourced under Open Government Licence v3. No proprietary datasets.
7. Regulatory Alignment
PRA SS1/23 (Model Risk Management)
Documentation structured to support vendor model assessment by regulated firms. Published methodology, accuracy monitoring, confidence indicators, and per-valuation audit trail.
Basel 3.1 (expected January 2027)
Portfolio revaluation capability for capital adequacy compliance. 10% threshold monitoring. Batch and API delivery for scalable portfolio coverage.
IVS 105 (Valuation Models), sections 30–50
Model characteristics documentation, validation methodology, limitation acknowledgement.
EAA ESSVM 3rd Edition (2022)
Methodology disclosure, confidence scoring on common 0–7 scale, segmented accuracy reporting.
RICS Red Book Global Standards (January 2025)
Consistent with PS 1.3 (statistical valuation), PS 1.6 (AVMs), and VPS 5 (valuation models) disclosure requirements.
8. Further Information
Further technical detail is available on request to organisations conducting vendor due diligence.
A sample valuation report is available at gadsdenvaluations.com/sample-report.
Contact: sales@gadsdenvaluations.com • gadsdenvaluations.com
Further technical detail
Available on request to organisations conducting vendor due diligence.
Contact sales@gadsdenvaluations.comThis document is for informational purposes. AVM outputs are statistical estimates, not formal valuations. Where regulation or contract requires a written valuation, independent professional review is necessary.