Why this note exists

The geometry read of the 745-plan census (the canonical thesis-wide space count of 12,849 spaces, on which the dimensional and generator pipelines rest) yields a set of quantitative design references that the empirical chapter and the Chapter 9 generator draw on. This note collects them: observed room-size targets, the dimensional grid, fixture packing densities, the kit-reuse ratio, and the context-conditioned size rules. Every figure is a descriptive statistic over a complete enumeration: an observed band a designer reads and dials within, not an estimate or a fitted target. Over a complete population the median and its interquartile range are the population’s own values, not estimates of an unobserved one, so no measure of sampling variability attaches.¹ Because printed dimensions are present for 7,287 of the 12,849 spaces (56.7 per cent: structurally, the habitable rooms a buyer evaluates), the size tables describe that dimensioned subset, while counts (kit reuse, packing density, served-to-serving balance) use the complete inventory and are the more robust figures.

This collection differs in kind from the two reference traditions it sits beside. Unlike a normative dimensional handbook (Neufert’s Architects’ Data; the ISO 2848 grid of Appendix H.4), whose figures are prescribed targets, these are measured central tendencies and spreads read off what Australian project builders actually drew. And unlike Alexander’s pattern language, whose patterns are qualitative and author-asserted,² each reference here carries a numerical scope and an observed spread.

0. Census enumeration reconciled: the three space counts and four category counts

Chapter 8 reports the same 745-plan census through three pipelines that each count spaces on a different basis, and the space taxonomy is reported at four reference points: the census category count, its two-stage componential consolidation, and a legacy topological subset retained for auditability. The figures appear in different Appendix H modules for different purposes, so this table gathers them in one place and states, where one count derives from another, the transform that carries it across. It reconciles the structure of the enumeration; the per-figure numeric derivations it references (in particular the occurrence-to-geometry delta and the category reduction) are the subject of a separate data-quality reconciliation and are not re-derived here.

Space counts. Three pipeline reads of one census:

Category counts. Four reference points:

Of the 12,849 canonical spaces, printed dimensions are present for the dimensioned subset used by the size tables below (Section 1); the count-based figures (kit reuse, packing density, served-to-serving balance) use the complete 12,849-space inventory. The precise size of the dimensioned subset, and the small residual discrepancies between the count bases recorded across the Appendix H modules, are registered to the same data-quality reconciliation rather than adjudicated in this note.

1. Room-size targets by category

For each category the median floor area is reported with its interquartile range (IQR) and quartile coefficient of dispersion (QCD, a scale-free spread measure), with the median long and short side. The QCD separates the categories a designer may treat as standardised (sized to a fixed object) from those that absorb residual area.

Categories with fewer than twenty dimensioned instances are reported in the data file but flagged small-n. The most standardised categories are the garage (QCD 0.087), main bedroom (0.145) and media room (0.154): each sized to a fixed object; the most variable are the store (0.637), porch (0.568) and alfresco (0.408): the leftover and outdoor spaces that absorb whatever area remains.

1.1 Context-conditioned size targets (the generator’s sampling vocabulary)

Room size is conditioned on context; the strongest conditional levers, read directly off the census, are:

• The main bedroom grows with the dwelling; the secondary bedroom does not. Median main-bedroom area rises 12.3 → 13.9 → 14.3 → 16.8 m² across two-, three-, four- and five-plus-bedroom dwellings, while the secondary bedroom holds near 10.8 m². The pooled bedroom median appears to fall as bedroom count rises, but that is a composition effect, larger dwellings hold a higher share of (smaller) secondary bedrooms, not a shrinking of any one room.
• Living scales with its graph role, not the bedroom count. A living space that is a circulation hub has a median area of 23.2 m² against 15.1 m² for a leaf living space.
• The garage is bimodal: a single garage clusters near 6.0 × 3.2 m (n = 140), a double near 6.0 × 5.8 m (n = 425), doubles outnumbering singles about three to one.

These conditional bands are the vocabulary the Chapter 9 generator samples (full cell table in the geometry-census analysis bundle).

2. The dimensional grid

Of 14,574 printed room dimensions, 99.6 per cent are multiples of 5 mm, 99.5 per cent of 10 mm, 89.4 per cent of 25 mm (equivalently 89.4 per cent of 50 mm: only four printed values are multiples of 25 but not 50), 87.3 per cent of 100 mm, and 35-36 per cent of 150 and 300 mm. Australian project-home room dimensions therefore sit on a 50/100 mm grid: the same dominant metric grain the product corpus exhibits (the 50 mm micro grain of Appendix H.4), and coarser only than its 25 mm sub-module. The single most common exact dimension is 3,000 × 3,000 mm, and 3,000 mm is the modal short side; as rooms enlarge both sides grow, but the long side grows faster than the short (a factor of about 2.2 against 1.8 across long-side quintiles), so the room lengthens faster than it widens and the aspect ratio rises.

These percentages describe how project builders currently draw rooms; the grain they reveal, 50/100 mm, is a description of the stock, not the thesis’s prescription. The grid the thesis prescribes for dimensioning room modules is the coarser 150 mm meso grid, and the two are not in tension. The 100 mm figure is the resolution at which the existing stock is drawn; 150 mm is the grain at which room modules compose with least combinatorial misfit, derived as a calibrated design choice in the integration of Section 8.50. On the composability axis a coarser grid is the better one: snapping the census to 150 mm cuts the distinct room-module catalogue from 1,770 to 1,117 rectangles and the effective module vocabulary from 349 to 203 against the 100 mm grain, but 150 mm is the coarsest grid that secures that gain while keeping the 95th-percentile room within 50 mm of its drawn size; a 300 mm grid would double that displacement to 100 mm and would foreclose the substantive room variation the figures above record. The 150 mm meso grid therefore organises the 100 mm-grained stock rather than contradicting it.

2a. The meso-grid calibration: composability, distortion, and standardisation

The 150 mm meso-grid selection of Section 8.50 rests on the battery set out in full here, every figure descriptive over the 745-plan geometry census (7,287 dimensioned rooms; 3,655 interior adjacencies with both endpoints dimensioned); the corpus is a complete enumeration, so no sampling variability attaches. The selection turns on two axes that move in opposite directions as the grid coarsens. Fit (the share of room dimensions that are exact multiples of the grid) always favours the finer grain and is a degenerate criterion (Section 8.21). Composability, how small a module vocabulary the grid produces and how readily modules share a commensurate edge, improves as the grid coarsens, paid for in distortion (how far a room must move to reach the grid). Treating the grid as a lossy quantiser, the rate (bits to name a module, log-2 of the effective module vocabulary) falls and the distortion rises monotonically with coarseness:

Because composability has no interior optimum (it improves all the way to 600 mm), the meso grid is fixed by a distortion tolerance, the largest displacement a room may suffer while still reading as the same room. The coarsest grid whose 95th-percentile room stays within a tolerance T is unique:

The 150 mm meso grid is exactly the choice of a 50 mm tolerance: the ISO half-module M/2, the coarsest sub-module the standard recognises and a displacement below the threshold at which a room reads as a different size. Tightening the tolerance to 25 mm would select a 75 mm grid; loosening it to a perceptible 100 mm would admit 300 mm. The selection is therefore closed under a stated, audited tolerance rather than asserted.

The result holds across the census and across room types, with one informative exception. Both strata return a 50 mm 95th-percentile displacement at 150 mm (effective modules 222 in the August stratum, 186 in the October delta), and the selection is stable to subsampling: withholding any one-fifth of the dimensioned corpus leaves the 95th-percentile displacement at 150 mm unchanged at 50 mm and the tolerance-bounded selection at 150 mm across all five disjoint folds, mirroring the base-module robustness reported at Section 8.22. By module type at 150 mm, the habitable modules all hold within the 50 mm tolerance (bedroom (n = 2,587; effective modules 55; p95 50 mm), living (n = 1,696; 272; 50 mm), kitchen (n = 454; 116; 50 mm), outdoor (n = 1,561; 187; 50 mm), and dwelling-other (n = 127; 86; 50 mm)) while the small service modules reach 60 mm: sanitary (n = 373; 77; 60 mm), circulation (n = 49; 42; 60 mm), and entry (n = 82; 52; 60 mm). These are the tightly packed wet and circulation spaces, whose internal components are dimensioned at the finer 50 mm micro grain rather than at the room meso grid; the exception is the micro-meso separation showing through, not a failure of the meso grid. The 150 mm value is a design prescription, the grain at which the generator dimensions its room modules, not the 100 mm grain on which the existing stock is drawn.

3. Fixture packing density

Median floor area per contained fixture, for the categories that pack fixtures: toilet 1.57 m², bathroom 1.86, ensuite 2.08, laundry 2.68, kitchen 3.00, pantry 3.35. Wet rooms are the most tightly packed spaces: density peaks exactly where rooms are smallest and most obligatorily coupled to a host.

4. Kit reuse and the served-to-serving balance

A median plan draws its 17 spaces from about seven distinct geometric primitives, a reuse ratio of about 2.4: each primitive instantiated two to three times; a whole dwelling is drawn from roughly seven kinds of rectangle. A median plan has 7 serving spaces against 10 served, with serving spaces about 39 per cent of all spaces under the narrow definition used here (circulation, service and storage, sanitary, and entry); the share is sensitive to that definition, rising toward one-in-two if outdoor and parking infrastructure are counted as serving.

All figures descriptive over the complete 745-plan census; independently re-derived from the canonical datasets. CANDIDATE until operator MR-13.