Methodology

PlanBuild.AI assesses whether an Australian residential lot can host a secondary dwelling (a fixed 6 × 10 m / 60 m² unit) under SEPP (Housing) 2021 and the local council DCP. Every address runs through the same staged pipeline; the verdict and the 10 screening rules are identical for every user.

Geometric convention (load-bearing)

Lot polygons come from the NSW cadastre as [lon, lat] rings in EPSG:4326. All areas, lengths, buffers and setbacks are computed by reprojecting to EPSG:3308 (NSW Lambert Conformal Conic) so units are true metres. The cadastre's shape_Area attribute is never trusted — it is Web Mercator and over-reads by roughly 30 % in Sydney.

Data sources

• ArcGIS World Geocoder — address → lat/lon.
• NSW Cadastre (SIX Maps) — lot polygon + ID.
• NSW Planning Portal EPI — zoning, minimum lot size, heritage.
• NSW Bush Fire Prone Land + Flood Planning — hazard overlays.
• NSW Elevation & Depth contours — lot-average slope.
• Microsoft Global ML Building Footprints — existing buildings (calibrated +20 %).
• NSW SIX Maps imagery — the three site figures + the close-up aerial.

Pipeline stages

1. Geocode the address (top match, score ≥ 80).
2. Cadastre + planning: lot polygon, area (EPSG:3308), zoning, MLS, hazard overlays.
3. Buildings: Microsoft ML footprints, calibrated +20 %, refined by a per-lot vision trace.
4. Frontage (v12): consecutive road-facing edges, with a battle-axe exception.
5. Slope (v3): lot-average from contours intersecting the lot, with a big-lot exception.
6. Placement (v3): brute-force a compliant 6 × 10 m pad with ≥ 3 m building clearance.
7. Screening: the 10 rules in order → verdict + rationale.
8. Figures + report: three site figures and a branded Word / PDF report.

Building footprints — calibrated MS + vision trace

Microsoft ML Buildings misses about a quarter of houses entirely and under-counts footprint by a median ~20 % where it does detect. PlanBuild.AI therefore applies a +20 % calibration and, for borderline or multi-building lots, overrides with a vision trace of the close-up aerial. The CV-refined coverage is what drives Rule 6.

Deliberately out of scope

BASIX / NCC energy compliance, stormwater & drainage, sewer / Sydney Water Section 73, tree preservation orders, and cost estimates are not assessed. Where relevant the report points to the appropriate professional service.

Indicative pre-screening only — not formal planning, building or financial advice.