Why this note exists

The lexicon defines standard room names as formulae over distinctive feature bundles, so a category means the same thing for every reader and outside this corpus. Two names denote the same category exactly when they share a bundle; names with no real difference are collapsed. It answers a question the co-occurrence analysis (design rule DR-5) shows cannot be answered by co-presence: because plans are near-uniquely composed, a room’s identity is carried by its features, not by what it is drawn next to. As a classification of “what is,” the lexicon is a descriptive (analysis-and-description) construct.¹

1. The minimal load-bearing feature set is four

Across the 47 realised categories, four features fully differentiate every genuinely distinct category, function · host · fixture signature · edge, yielding 36 distinct bundles (the remaining eleven names are genuine collapses). Enclosure, location and substrate are readable descriptors that ride along; storey is excluded as under-marked.

2. Access is a topology, not “privacy”

The distinctive fact about how a space is reached is its access topology, read from the plan graph, not a vague notion of privacy: off-circulation (entered from a hall), nested (entered through a single host room: the walk-in / ensuite structure), open-plan (a doorless merge), attached (an external space attached to a host), and detached (freestanding). The host, the room one passes through, generalises “private from the bedroom”: a walk-in robe and a walk-in pantry are the same access structure (nested), differing only in host (bedroom versus kitchen).

3. Definitions that fall out of the features

• Ensuite = a bathroom nested in a bedroom: identical to a bathroom except in access topology; that, not its size or fixtures, is its definition.
• Walk-in family = a storage space nested in a host, parameterised by host and contents: walk-in robe (bedroom + robe), walk-in pantry (kitchen + pantry shelving), butler’s pantry (kitchen). The reach-in counterpart is the shallow, non-enterable cupboard (linen).
• Alfresco = the roofed outdoor room (covered + external + attached, host = living); porch = the open outdoor arrival threshold; balcony/deck = the open living-attached platform (balcony its upper-storey instance); garage versus carport = enclosure (walled versus open-sided).

4. Substantive vocabulary findings (collapses, operator-confirmed)

family / lounge → living; main + secondary bedroom → bedroom (main = a size-and-master-suite variant); studio → study; several small-n outdoor types → one detached outdoor amenity; activity / breakout → rumpus. Kept distinct: store ≠ walk-in robe (general versus clothes storage; a store is general-access, a walk-in robe is nested in a bedroom). Data-quality flag (not a merge): in the census a large share of spaces labelled “store” actually hold a robe and are bedroom-hosted: mislabelled built-in robes, flagged for an MR-13 reclassification; the label is wrong, the distinction is not.

5. How the lexicon predicts size (the bridge to DR-3)

Because each distinctive feature carries a size signature, a category’s size is the intersection of its features. A bathroom (median 5.5 m²) is enclosed (compact) + internal (compact) + off-circulation (a small leaf) + wet-function (smallest class) + a three-piece fixture set (packs about three fixtures into a few square metres): every feature pulls it small and tight. The alfresco is the mirror image (covered + external + attached → large and variable). The lexicon thus does explanatory work, not just naming: it says why a category sits where it does in the size distribution. Descriptive throughout; CANDIDATE until operator MR-13.