Basement Risk Index methodology
How the score is built, what is measured versus modeled, and what it does and does not mean.
The Basement Risk Index (BRI) is a 0–100 score that rates metro Detroit communities and neighborhoods on their relative structural exposure to basement water. It is built entirely from public data. This page documents exactly how it works, because a public-records resource should be transparent about its own numbers.
What goes into the score
The BRI combines housing-vintage measures with documented flood history. The two largest inputs are both real U.S. Census measures of housing age, which is the strongest structural predictor of basement water problems in this region:
- Share of homes built before 1960 (weighted ~60% of the housing component). Sump pumps, exterior weeping tile, and backwater valves became standard only after the 1960s; older homes rely on original clay drain tiles that fail over time.
- Median year the housing was built (weighted ~40% of the housing component), which captures how old the typical home is, not just the share that is old.
- Documented flood records for the City of Detroit: 13,433 water-in-basement reports (as of June 2026) logged in the city's Improve Detroit / 311 system since 2023 are incorporated into Detroit's score. These are the ongoing, post-2021 backups recorded by the current 311 system, not the 2021 event itself; the June 2021 storms, which brought a federal disaster declaration to Wayne County, are the context for why documented flood history matters.
Regional factors, the heavy clay soil that blankets southeast Michigan and the combined-sewer systems common in the older inner ring, are the reason housing age predicts risk so well here. They are described as context; they are not separately computed per-community inputs in the current version.
What is actual versus modeled
This distinction matters, so we state it plainly:
| Area | Basis | Type |
|---|---|---|
| City of Detroit | Census housing age + 13,433 documented 311 water-in-basement reports (2023-present, as of June 2026) | Actual + modeled |
| Suburban communities (Oakland, Macomb, the rest of Wayne) | Census housing-age measures; no municipal flood records integrated yet | Modeled |
In other words: Detroit's score reflects real reported flooding; suburban scores are a model of structural risk from housing data, not a record of reported flooding. We are working to incorporate county sewer-backup claim data for the suburbs in a future version.
How the score is normalized
For each community we compute a housing-vintage component from the two Census measures above, add the documented-flood component where we have it, and then rescale the result across all communities to a 0–100 range, so the number tells you where a community stands relative to the rest of metro Detroit. The metro median is currently 35. The neighborhood-level map shades census tracts on the same housing-age basis.
Neighborhood and ZIP-level Detroit data
For the City of Detroit, the 311 water-in-basement record can be examined below the community level. The city's current 311 system holds about 13,400 "Water In Basement Investigation" reports dated 2023 to the present, geolocated to neighborhood and ZIP. We measure a neighborhood's basement-backup intensity as its share of all local 311 activity, which controls for neighborhood size and how heavily residents use the system, benchmarked to the citywide rate of about 4.8 percent.
Pairing this record with Census housing and demographic data lets us ask who carries the burden. Our analysis of who bears Detroit's basement-flood burden finds that backups concentrate in the city's oldest, predominantly Black, lower-income neighborhoods, driven by structural factors (aging housing and combined sewers), and it documents the method, the correlations, and the limits in full.
What the score does not mean
- It is not a prediction for any individual property. Two homes on the same block can differ entirely based on grading, sump pump, and maintenance.
- It is not engineering, insurance, or financial advice. Only a qualified professional can assess a specific home.
- It is a relative score, not an absolute probability. A score of 80 means higher structural exposure than a 40, not an 80% chance of flooding.
- A low score is not zero risk on clay soil. Symptoms at your own home matter more than any average.
Data sources and dates
- U.S. Census Bureau, American Community Survey 2022 5-year (tables B25034, B25035, B25077, B19013, B25003), by census tract and county subdivision. Retrieved June 2026.
- City of Detroit Open Data, Improve Detroit (311) water-in-basement reports. Retrieved June 2026.
- U.S. Census TIGER/Line community and tract boundaries.
- Federal flood and disaster records, including the 2021 Wayne County declaration.
Basement Risk Check is independent and not affiliated with or endorsed by any government agency. We are happy to share the underlying data and calculation detail with any journalist or researcher: [email protected].