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.
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. See the full methodology and sources. Download the raw per-city data below.