Sinkhole risk in Orange County, FL: Pockets of it

Pockets of it

Soluble rock at the surface or under thin cover in part of the county.

On soluble rock: 100%
At or near the surface: 7%
Buried under cover: 93%

What to do about a house in Orange County

Check the parcel against your state survey sinkhole map, and ask for an inspection if cracks, depressions or sticking doors show up.

Standard Florida homeowners policies cover only catastrophic ground cover collapse; full sinkhole coverage is a separately priced option insurers must offer.

That works out to roughly 903 of Orange County's 903 square miles on soluble rock, 61 of them with the rock at or near the surface. With about 1,533,646 residents (1,698 per square mile), there is effectively nowhere in the county off the soluble rock, town or country. The figures come from 280 map points about 1.8 miles apart, so a pocket smaller than that can be missed or overstated.

Two things to read before deciding: what Florida insurers have to cover, and why gypsum and salt move faster than limestone.

Counties around Orange County

The nearest county rated sinkhole country is Sumter County, FL, about 47 miles west. 6 of the 6 closest counties land in the same band, so this is a regional pattern rather than a local quirk.

Seminole County, FL 17 mi northeast · 29% at surface
Lake County, FL 29 mi northwest · under 1% at surface
Osceola County, FL 33 mi south · 3% at surface
Volusia County, FL 39 mi north · 22% at surface
Brevard County, FL 41 mi east · 40% at surface
Polk County, FL 45 mi southwest · 3% at surface

What Orange County is built on

The largest mapped soluble unit here is the Hawthorn Group, Coosawhatchie Formation (limestone), Eocene in age, covering about 50% of the county. Next is the Shelly sediments of Plio-Pleistocene age at 35%.

The county also lies over the Floridan shelf, a deep salt or gypsum basin. Deep beds rarely cause surface collapse on their own, but wells and mining into them have.

Against the rest of Florida

Orange County ranks 56 of 67 in Florida for soluble rock at the surface, and sits above 65% of US counties on that measure.