How We Score Site Risk

Our composite risk score combines four COPE categories with industry-standard weightings:

The composite score (0-100) represents overall site risk. Scores below 25 indicate low risk with standard construction costs. Scores 25-50 suggest moderate risk with 5-15% cost adjustments. Scores above 50 indicate elevated risk requiring specialized engineering or materials.

The Occupancy score evaluates whether the site's zoning and regulatory environment supports the intended use — particularly ADU (Accessory Dwelling Unit) construction.

Data Sources

• Maricopa County GIS — parcel zoning designation, lot size, existing structures
• Jurisdiction-specific rules — ADU ordinances for Phoenix, Scottsdale, Tempe, Mesa, Tucson, Cave Creek, and Maricopa County

What the Score Means

Regulatory Context

Arizona HB 2720 (signed May 2024) requires cities over 75,000 population to allow ADUs by right on single-family lots. HB 2928 (signed May 2025) extends this to counties statewide. These laws limit HOA ability to prohibit ADUs and set maximum regulatory requirements jurisdictions can impose.

Each jurisdiction has specific requirements for setbacks, maximum ADU size, parking, and utility connections. Our permit checklist reflects the current rules for each city.

The Construction score evaluates subsurface conditions that affect foundation design, excavation costs, and material selection.

Data Source

USDA Soil Data Access (SSURGO) — the national soil survey database maintained by the Natural Resources Conservation Service. Provides engineering-grade soil property data at parcel-level resolution.

Factors Scored

• Caliche likelihood — calcium carbonate hardpan common in Arizona desert soils. Increases excavation costs significantly when present at shallow depths.
• Shrink-swell potential — expansive clay content that causes foundation movement. Measured by the coefficient of linear extensibility (COLE).
• Depth to bedrock — shallow bedrock (<40 inches) requires specialized excavation equipment.
• Corrosion risk — soil chemistry that accelerates degradation of steel reinforcement or concrete. Affects material selection and protective coatings.
• Drainage class — how quickly water moves through the soil. Poor drainage increases foundation moisture risk.

The Protection score estimates the ISO Protection Class based on proximity to fire services. Protection Class directly affects property insurance premiums — lower classes mean lower rates.

Data Source

OpenStreetMap Overpass API — fire station locations and fire hydrant positions within a 10-mile radius of the property. We calculate straight-line distances and estimate the Protection Class.

How Protection Class Is Estimated

• PC 1-4 — Fire station within 5 miles AND hydrant within 1,000 feet. Excellent fire protection.
• PC 5-6 — Fire station within 5 miles, hydrant within 1,000 feet but limited water supply indicators.
• PC 7-8 — Fire station within 5 miles but no hydrant within 1,000 feet.
• PC 9 — Fire station within 5 miles but no nearby hydrant infrastructure.
• PC 10 — More than 5 miles from nearest fire station. Unprotected for insurance purposes.

Flood zone designation determines whether flood insurance is required and significantly impacts both construction costs and ongoing operating expenses.

Data Source

FEMA National Flood Hazard Layer (NFHL) — the official flood map used by lenders and insurers. Queried via ArcGIS REST services for the exact parcel location.

Zone Designations

• Zone X (Minimal) — Outside the 500-year floodplain. No flood insurance required by lenders.
• Zone X (Moderate) — Between the 100-year and 500-year floodplain. Insurance recommended but not required.
• Zone A / AE — Within the 100-year (1% annual chance) floodplain. Flood insurance required for federally-backed mortgages. Base Flood Elevation (BFE) determines minimum finished floor height.
• Zone AH / AO — Shallow flooding areas. Special drainage and elevation requirements.
• Zone V / VE — Coastal high-velocity flood zones. Strictest building requirements.

Wildfire risk assessment identifies properties in or near the Wildland-Urban Interface (WUI) where structures face elevated fire exposure from surrounding vegetation.

Data Source

USFS Wildfire Hazard Potential (WHP) — a nationwide raster dataset from the US Forest Service that classifies wildfire risk to potential structures based on vegetation, topography, and fire weather patterns.

Defensible Space

Arizona requires defensible space zones around structures in wildfire-prone areas: Zone 1 (0-10 ft) should be non-combustible, Zone 2 (10-30 ft) should have reduced fuel, and Zone 3 (30-100 ft) should have thinned vegetation. These requirements affect landscaping costs and ongoing maintenance.

Seismic hazard assessment determines the earthquake design requirements for new construction based on the site's Peak Ground Acceleration (PGA) values.

Data Source

USGS National Seismic Hazard Model (NSHMP) — probabilistic seismic hazard analysis for any location in the US. We use the 2% in 50 year exceedance probability (standard for building codes).

Seismic Design Categories

• SDC A — Very low seismic risk. Standard construction. Most of eastern Arizona.
• SDC B — Low seismic risk. Minor additional reinforcement. Most of the Phoenix metro area.
• SDC C — Moderate seismic risk. Specific structural detailing required.
• SDC D-F — High seismic risk. Significant structural engineering requirements. Rare in Arizona.

The composite score is a weighted average of all COPE category scores:

Exposure is itself a composite of flood, wildfire, and seismic sub-scores, weighted by the relative hazard severity at the specific location.

Using the Composite Score

All data comes from publicly available government APIs. No proprietary or paid data sources are used in Phase 0.