Research
Five datasets on what actually threatens a basement
Every figure on this site traces to a primary source. These are the five original datasets behind it — flood claims, groundwater, frost, soil, and permits — each read from public records, mapped to the cities people search for, and free to cite with a link.
29%
of basement flood claims were filed outside the mapped floodplain
The flood map is about rivers, not your basement. And this is a floor, because flood insurance is mostly bought only inside the zone.
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1.8 ft
median depth the seasonal water table rises to, against a 7 ft basement floor
In every rated city the seasonal high groundwater rises above a typical basement floor. That is what a sump pump is for.
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137/yr
freeze-thaw cycles in Lakewood, the hardest-hit city we track
Each crossing of freezing heaves the ground and works foundation cracks open. Ten years of reanalysis, every city ranked.
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40 cities
sit on ground that is mostly high shrink-swell (expansive) clay
Clay that swells and shrinks with moisture cracks foundations by moving them. The Texas and Front Range clay belt, measured and ranked.
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11 of 118
cities charge a flat fee to permit foundation work
Everywhere else the permit bill scales with your project. Each city read from its own published fee schedule and linked.
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Planning-cost reports
Alongside the sourced data, regional planning estimates for the two biggest jobs. These are modeled ranges, not surveys — a starting point to sanity-check real quotes.
For journalists and researchers
Each report includes its method and source, and we are explicit about limits too — the cost figures are modeled, and the soil data misses expansive bedrock — because a number you can trust is the whole point. Cite the specific report page, or see the full methodology and sources. Download the raw per-city data below.