Status: accepted

Accepted — merged with intent to implement.

RFC 0114: Record the area measurement standard behind per-area metrics

Accepted by the UWMD maintainers, 2026-10-21, as drafted (owner: "RFC 0113 (#476) and RFC 0114 (#477) accepted as drafted."). Origin: issue #343 finding M10, left open by the metric variants table in spec/metrics/README.md ("whether to record the area measurement standard"). It adds an optional, validated member, so it is normative. No formula changes.

Summary

price_per_sqft, price_per_nrsf and the other per-area metrics divide by the class's primary size field: rentable SF for office and industrial, GLA for retail, NRSF for self storage. Nothing in a record says how that area was measured. BOMA, IPMS, REBNY and RICS give different areas for the same building, and a reader comparing two records' price per SF cannot tell whether they measured alike. This RFC adds an optional property.area_measurement that names the standard and edition behind the stated areas. It changes no metric and does not convert between standards.

Motivation

• Same building, different denominators. Rentable area under one standard can differ from another by several percent. That moves price per SF as much as a real price change would.
• Lenders and appraisers state the basis. Appraisal review compares units of comparison on a stated basis (OCC Comptroller's Handbook). The record has nowhere to carry it.

Proposed change

1. Format §4.1 property. Optional area_measurement:

   "area_measurement": {
     "standard": "boma | ipms | rebny | rics | other",
     "edition": "string",
     "note": "string"
   }

   standard is a closed vocabulary. An unknown value is refused, as other closed vocabularies are (D2). edition names the publication, for example "ANSI/BOMA Z65.1-2017", as free text. note is optional. The member applies to every area-valued size field the record states.
2. Validation. A malformed member (unknown standard, or edition not a string) is an error under a new PROP- or CLS- code assigned at implementation. An absent member is not a finding (D3).
3. No metric change, no conversion. The per-area formulas are unchanged, and a Verifier does not compare or convert areas across standards.
4. Variants table. The per-area row says the basis is recorded in property.area_measurement when stated.

Compatibility analysis

No compatibility path (prelaunch; the prelaunch policy). The member is optional, so no existing record changes meaning.

Conformance impact

New cases: a valid member on an office record, plus refusals for an unknown standard and a non-string edition. No expected metric output changes.

Reference implementation

The Format text and property schema, the validator check and its code (verify-codes registry), the Python validator, the cases and the variants table row.

Alternatives considered

• Require it at full_underwrite. This would make the basis visible on every credit file. It is a stronger rule than the evidence asks for. Not proposed; see D3.
• One id per standard and area type (for example boma_2017_office_rsf). This is more precise, but the vocabulary would grow with every edition. Not proposed.
• Convert to a common basis. No conversion between standards is exact. Rejected.

Decisions (accepted 2026-10-21)

#	Question	Proposal	Why / alternative
D1	Where the basis lives	property.area_measurement, one per record	The size fields live in property (§4.1). Alternative: one entry per size field
D2	standard vocabulary	Closed: boma, ipms, rebny, rics, other; edition as free text	House pattern of closed vocabularies. Alternative: free text
D3	When it is required	Never; absent is not a finding	Records the basis without a new obligation. Alternative: required (or a warning) at full_underwrite
D4	Effect on metrics	None; no cross-standard comparison or conversion	UWMD verifies stated figures; a conversion would be a new convention
D5	Versions	None allocated; prelaunch 4.x	RFC 0091 D6

Prior art

• Issue #343 (M10); spec/metrics/README.md "Variants in use" (#451).
• Protocol §XIII and RFC 0027 (primary size fields per class).