Build a local comparable pool without confusing distance with similarity

Start with a candidate pool, not a valuation set

An exact postcode can contain only a handful of completed transactions, particularly for one property type. A nearby-postcode search can make the evidence review more useful, but it changes the question from ‘what sold in this postcode?’ to ‘which nearby sales might deserve inspection?’

PropertyMetrics keeps the subject postcode, the nearby postcode and centroid distance on every candidate. That distance is a discovery aid. It does not measure street character, school catchments, station access, noise, outlook or the route between properties.

Remove legal and physical mismatches first

Filter tenure and broad property type before looking at price. A leasehold flat and a freehold terrace can be geographically close while answering different market questions. Next compare floor area, bedroom count, plot, parking, condition, lease terms and any material extension.

The public Price Paid feed does not contain those attributes. Add them from particulars, EPC records, surveys or direct inspection, and record the origin rather than filling gaps from memory.

• Keep the exact-postcode set available as a separate reference.
• Prefer a smaller explainable set to a larger automatic average.
• Do not use centroid distance as an adjustment formula.
• Record why every selected transaction remains useful.

Treat time as another difference to explain

A transaction several years old can be physically similar but needs a time-period discussion. A recent sale can be physically irrelevant. Avoid choosing on date alone and avoid applying a general house-price index mechanically to one property without explaining the chosen index and geography.

When the candidate set crosses a changing market period, show both recorded and adjusted figures. Keep the recorded completion price immutable.

Stop when the evidence remains heterogeneous

If every candidate needs a large or poorly evidenced adjustment, the pool has not become stronger merely because it is larger. Document the weak match and seek better particulars, a wider but carefully controlled search, or professional valuation evidence.

Make the search footprint auditable

Save the subject postcode, every contributing postcode, centroid distance, returned record count and source state. This is more informative than saying only that the search covered ‘the local area’. It also shows whether the pool changed because a new sale appeared or because one source failed.

When presenting the result, show the exact-postcode summary beside the broadened summary. A reviewer should be able to see what the expansion added, how it changed the property and tenure mix, and which candidates were ultimately retained.