Methodology
Data sources, coverage and limits
The lot check combines public map data with the ADU rules in the adopted code. Here is exactly where each piece comes from, how current it is, and what a result can and can’t tell you.
Where detailed lot checks work
| Area | Coverage | Rules checked |
|---|---|---|
| City of Grand Junction, CO | Detailed parcels, zoning, buildings, hazards, utilities, imagery | October 12, 2026 |
| Unincorporated Mesa County, CO (Clifton, Orchard Mesa, the Redlands, Fruita and Palisade areas) | Detailed parcels, zoning, buildings, hazards, utilities, imagery | October 12, 2026 |
| City of Olympia, WA | Detailed parcels, zoning, buildings, sewer mains, hazards | October 13, 2026 |
| Everywhere else | Not yet The guides and calculators apply; the lot check says when an address isn’t covered | — |
Where the data comes from
| Information | Source | How current |
|---|---|---|
| Lot lines and parcel size | Mesa County GIS; Thurston County GIS | Read live at each lookup |
| Zoning district | City of Grand Junction and Mesa County zoning; City of Olympia zoning | Read live at each lookup |
| ADU rules (setbacks, size, height, coverage, parking) | The adopted municipal and county code, written into plain language with the section cited; state ADU laws (Colorado HB24-1152, Washington HB 1337) | Checked on the dates above, and when the code changes |
| Existing buildings | Mesa County building footprints; City of Olympia buildings; USA Structures (ORNL / FEMA, CC BY 4.0) elsewhere | As published by each source |
| Aerial imagery | Mesa County / City of Grand Junction 2024 imagery; USDA NAIP via the USGS National Map; City of Olympia base map | Flight year shown on the map |
| Elevation, slope and drainage | USGS 3D Elevation Program | Read live at each lookup |
| Flood zones | FEMA National Flood Hazard Layer (county copy where available) | Read live at each lookup |
| Wetlands | U.S. Fish & Wildlife Service National Wetlands Inventory | Read live at each lookup |
| Electric provider | HIFLD Electric Retail Service Territories | Read live at each lookup |
| Sewer and water | County and city service layers; City of Olympia sewer map | Read live at each lookup |
| Address matching | Mesa County locator; U.S. Census Bureau geocoder | Read live at each lookup |
What a result is, and isn’t
| Level | Who produces it | What you can rely on it for |
|---|---|---|
| Illustrative fit (this tool) | Automated, from public data and the code | A confident first conversation: is it worth pursuing, and what to ask |
| Surveyed fit | A licensed surveyor | Exact lot lines, easements and existing structures |
| Engineer-verified feasibility | Licensed engineers and designers | Grading, drainage, utilities and structure |
| Permit approval | Your city or county | Permission to build |
Known limits
- County parcel lines can be off by a few feet, and they don’t show easements.
- Private covenants and HOA rules aren’t included.
- Utility routes are proposals; where existing service lines enter the house isn’t mapped.
- Building footprints and imagery can be a year or more old.
- Local interpretation, variances and pending code changes are decided by planning staff.
- Cost and return figures are estimates with assumptions you can change, not quotes or financial advice.
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