> ## Documentation Index
> Fetch the complete documentation index at: https://docs.propx402.xyz/llms.txt
> Use this file to discover all available pages before exploring further.

# Hidden Cost Engine

> How PropX402 surfaces costs investors miss before closing

PropX402 automatically surfaces costs derived from property age, construction era, weather exposure, and flood zone status — things that never appear on a listing sheet.

## Insurance Estimate

Base rate: **0.8% annual property value**, adjusted for:

* Age surcharge: up to +60% for 80+ year homes
* Tornado/hail risk: up to +40% (NOAA data)
* Flood zone: +\$1,200/yr NFIP average if in flood zone

## Rehab Cost Estimate

Base cost per sqft by age (8–52 \$/sqft) × condition multiplier (0.2–1.8x):

| Condition | Multiplier |
| --------- | ---------- |
| Excellent | 0.2x       |
| Good      | 0.5x       |
| Average   | 1.0x       |
| Fair      | 1.3x       |
| Poor      | 1.8x       |

## Age-Based Risk Flags

| Risk               | Trigger           | Budget Impact              |
| ------------------ | ----------------- | -------------------------- |
| Lead paint         | Built before 1978 | +\$8K if Very High         |
| Knob & tube wiring | Built before 1950 | \$8–15K rewire             |
| Asbestos           | Built before 1980 | \$2–8K testing/remediation |

<Note>
  **Example — 1411 8th Ave SE, Cedar Rapids IA (built 1910)**

  Insurance: $142/mo · Rehab mid: $86,010 · Lead paint: Very High · Wiring: likely knob & tube · Asbestos: possible. None of this appears on the listing.
</Note>