Most underwriting errors that survive to the investment committee were introduced before the model was opened. They came from the site record: a lot area taken from a listing, a zoning district read as though it were a permission, an existing building assumed to be conforming because it is standing.
The parcel and zoning check is fifteen minutes of work. Here is what it consists of.
What a parcel record actually is
Every US property sits in a county assessment record. The identifier is called an APN in most of the country, a folio in much of Florida, a BBL in New York City, and something else again in a handful of jurisdictions, but the content is broadly the same: owner of record, legal description, lot area, building area, year built, a use or property class code, assessed value, and the transfer history.
Two things follow, and both get missed.
It is a tax record, not a survey. Assessor lot areas are frequently rounded, sometimes inherited from a decades-old deed, and occasionally simply wrong. They are the right starting point and the wrong finishing point.
Its use code is an assessment category, not a zoning designation. A parcel classed as commercial by the assessor may sit in a residential district; the two systems answer different questions and are maintained by different offices.
Why a zoning district code answers nothing on its own
"It's zoned C-2" is the beginning of the question. The buildable outcome depends on a stack of rules, and each layer can be the binding one:
- The use table. Whether your intended use is permitted by right, permitted conditionally, or not at all. Conditional means a hearing, and a hearing means time and risk that belong in the model.
- Density or intensity limit. Floor area ratio, units per acre, or both.
- Height limit, in feet and often also in storeys. The two can bind differently.
- Setbacks, lot coverage and open space, which together often make the FAR unreachable on an irregular or small lot. The envelope, not the ratio, is what you can actually build.
- Parking requirement, which on a constrained site is routinely the rule that decides the scheme.
- Overlays and special districts. Historic, coastal, airport, transit-oriented, planned development. An overlay can be more permissive or far more restrictive than the base district, and it is invisible if you only read the district code.
There is also the case of the building already there. An improvement that predates the current ordinance may be legal non-conforming: lawful to keep, but often not lawful to rebuild as-is if it is destroyed or substantially altered. If your plan involves major renovation, that distinction is a material assumption and belongs stated on the page, not discovered in diligence.
Where the data comes from, and which source governs
- County assessor or property appraiser, the parcel record: ownership, areas, year built, use code, assessed value, transfers.
- County or municipal GIS, geometry and dimensions, district boundaries, overlay layers, floodplain, and the neighbouring parcels you will need for any assemblage question.
- The municipal zoning ordinance, the rules themselves.
The ordering matters. The ordinance governs; GIS and assessor records describe. Where a GIS overlay layer and the ordinance text disagree, the text wins, and the disagreement itself is worth noting. It usually means the layer is stale.
The check, in order
- Confirm the identifier against the address. Addresses are assigned and reassigned; the parcel identifier is the stable key. Everything downstream should be keyed to it.
- Reconcile lot area between the assessor record and the GIS geometry. A gap of a few per cent is normal; a gap of twenty per cent means one of them is describing a different parcel, and you need to know which before anything is divided by it.
- Read the base district and then look for overlays. Two lookups, not one.
- Check the use table for your intended use rather than assuming a category. Permitted, conditional and prohibited are three different financial outcomes.
- Compute the envelope, not just the ratio: FAR against setbacks, height and coverage on the actual lot shape.
- Note the conforming status of any existing improvement.
- Pull the transfer history. A recent arm's-length transfer on the subject is the single most informative comparable you will find, and it is free.
Carry the source next to the figure
The practical discipline that prevents most of the damage is simple: every site figure that enters the model carries, next to it, where it came from and when it was read. Lot area from the assessor record dated this month is a different input from lot area from a brochure, and six weeks later nobody remembers which one went in.
This is the part worth automating. Titleman pulls the parcel record, the district and overlays, and the transfer history, and returns them as a page where each field shows its source and its date, so the zoning assumption in the underwriting can be traced back to the document that supports it rather than to whoever typed it.