How feasibility screening works, and what it cannot tell you
The feasibility screener checks a property against the planning rules we have encoded from public sources: the national standards for detached minor residential units, and the district plan provisions of each council we have wired up. It reads the zoning and overlay layers each council publishes, the parcel boundary, title records and building outlines from Toitū Te Whenua LINZ, and the lie of the land from LINZ elevation data. From all of that it produces a confidence tier for each kind of project you ask about.
The four tiers
Every result lands on one of four tiers. "Clearly eligible on current rules" appears only when every encoded check passed using verified data, which for a granny flat means the unit provably fits on the parcel once setbacks and existing buildings are measured. "Likely eligible, confirm with a professional" means the checks passed but some of what you told us could not be independently verified. "Needs professional check" means something real needs a human: an overlay touches the property, the title is a cross lease, the site is steep, or a piece of data simply was not available. "Not eligible on current rules" means a specific rule failed, and the result names it.
One principle sits under all of this: anything we could not check is treated as unknown, and an unknown always pulls the result down, never up. Silence is not clearance.
Where the data comes from
Council zoning and overlay layers are copied into our own store on a schedule rather than queried live, so every result records exactly which snapshot of the rules it was screened against, and reports print those dates and version numbers. Parcel boundaries, titles and building outlines come from LINZ under open licences. Money figures, where shown, are indicative low-to-high ranges built from configurable cost bands. They are screening context, never a quote and never a professional assessment of what anything is worth.
What this cannot tell you
A screening cannot see everything a professional can. It does not read the wording of consents or covenants on your title. It does not know the ground conditions, the state of the services at your boundary, or what your neighbours have consented. It measures buildings from aerial outlines, which can be out of date. Council data can lag behind plan changes, and plan rules themselves are in transition in several districts. Where our checks are incomplete for a council, the result says so rather than guessing.
Above all, a screening is not a decision. Nothing here grants, promises or implies consent for anything. The tool exists to tell you whether a professional conversation looks worth having, and to hand that professional a clear, traceable starting point.