Yes — you should test for radon before you buy a home in Sioux Falls. South Dakota has the highest average indoor radon levels in the country, and the eastern half of the state — including Minnehaha and Lincoln County — sits in the EPA’s highest-risk Zone 1.
Quick Answer: Radon is a colorless, radioactive gas and the second-leading cause of lung cancer. In South Dakota, about half of tested homes come back above the EPA’s 4 pCi/L action level — among the highest rates in the nation. Budget roughly $150 to $250 to test during your inspection, and $800 to $2,000 for mitigation if levels are high. The seller often pays.
Why radon is a bigger problem here than almost anywhere else
Radon forms as uranium in the soil breaks down, then seeps into homes through foundation cracks, sump pits, and floor drains. South Dakota’s geology makes that a statewide issue. The state Department of Agriculture and Natural Resources (DANR) classifies the entire eastern part of the state, where Sioux Falls sits, as Zone 1 — the EPA’s highest radon-potential category.
About half of South Dakota homes that get tested come back above the EPA’s action level of 4 picocuries per liter (pCi/L), and reporting from South Dakota Searchlight in April 2023 cited American Lung Association data ranking the state’s share of elevated tests among the highest in the country.
Why it matters for you as a buyer: radon is the second-leading cause of lung cancer after smoking, and the only way to know a specific home’s level is to test it. One house can test high while the home next door tests low — it comes down to that individual home’s soil, foundation, and ventilation.
How a radon test fits into your Sioux Falls purchase
The radon test almost always happens during your inspection period — the window after your offer is accepted when you’re checking the home’s condition. Most buyers add it to the general home inspection rather than hiring separately.
- Timing: A passive short-term test sits in the lowest livable level of the home for at least 48 hours under “closed-house” conditions, with windows and exterior doors kept shut.
- Who runs it: Your home inspector often offers radon as an add-on, or you can hire an NRPP- or NRSB-certified radon measurement provider.
- Cost: About $150 to $250 as part of a Sioux Falls inspection — see our breakdown of what a home inspection costs in Sioux Falls.
Because the result comes back during your inspection contingency, you still have room to negotiate — which is exactly why waiving inspections to win a bid can backfire here. If you’re weighing that, read should you waive the inspection to win a Sioux Falls offer.
New construction isn’t automatically safe, either. Builders in South Dakota aren’t required to install an active radon system unless local code calls for it, so a brand-new home can still test high. That’s one more line item to weigh in the new construction vs. resale decision.
What testing and mitigation actually cost
Testing is cheap. Fixing a high reading costs more, but it’s rarely a dealbreaker.
- Radon test: about $150–$250 as an add-on to your inspection.
- Mitigation system: about $800 to $2,000 installed; DANR puts the statewide average around $1,200 for an active soil-depressurization system.
- Operating cost: roughly $3 per month to run the fan, per DANR.
- Fan lifespan: about 11 years, with replacement running $145 to $300.
A mitigation system is a PVC pipe and a quiet, continuous fan that pulls radon from under the slab and vents it above the roofline. Even very high readings can be brought below the action level.
One free option worth knowing: DANR gives away 500 free radon test kits to South Dakota residents each year. That’s great for testing a home you already own — but for a purchase, most buyers use a professional test tied to the transaction timeline so the result is documented for negotiation.
Who pays for radon mitigation in a Sioux Falls deal?
There’s no law assigning the cost, so it’s negotiated — but in practice, sellers frequently end up covering it. Here’s why: once a seller knows a home tested high, South Dakota’s disclosure law means they’d have to reveal that to the next buyer too if your deal falls apart. (South Dakota requires a completed Seller’s Property Condition Disclosure Statement under SDCL 43-4-44 — more on that in what sellers have to disclose in South Dakota.)
Common ways it gets resolved:
- The seller installs the system before closing.
- The seller gives you a closing credit to install it yourself with your chosen contractor.
- You split the cost.
- The price drops by the estimated mitigation cost.
Two exceptions: on an as-is or estate sale, the buyer usually absorbs the cost, and on new construction the builder may leave it to you. This is the kind of thing I walk buyers through before we write the offer — knowing radon is likely and building the contingency in gives you leverage instead of a surprise.
Frequently Asked Questions
Is radon really a problem in Sioux Falls?
Yes. Sioux Falls sits in the EPA and DANR’s Zone 1, and about half of tested South Dakota homes exceed the 4 pCi/L action level — among the highest rates in the country. Because levels vary house to house, every home should be tested individually.
How long does a radon test take?
A standard short-term test runs at least 48 hours under closed-house conditions, so it fits inside a normal inspection period. Results usually come back within a few days.
What radon level requires mitigation?
The EPA recommends fixing your home at 4 pCi/L or higher and suggests considering a fix between 2 and 4 pCi/L. Above 4, plan on installing a mitigation system.
Does a radon system hurt resale value?
No. A documented, working mitigation system is a selling point in South Dakota, where buyers expect radon awareness. It shows the issue was identified and handled properly.
Can I use the free state test kit when buying?
You can, but for a purchase most buyers use a professional test tied to the inspection timeline so the result is documented for negotiation. Save the free DANR kit for a home you already own.
The bottom line
Testing for radon in Sioux Falls isn’t an optional extra — with South Dakota leading the nation in elevated readings, it’s a standard, low-cost step that protects both your health and your negotiating position. Get the test during your inspection, know the numbers, and you’ll be ready to handle a high result instead of being blindsided by one.
If you’re planning a purchase and want to know how to build radon and other inspection contingencies into a strong offer, grab the free Sioux Falls Buyers Guide and reach out anytime — I’m happy to walk you through it.
About Tyce Ortman
Tyce Ortman is a residential real estate agent with the Jeff Merrill Team at eXp Realty, serving Sioux Falls, South Dakota and surrounding communities including Brandon, Harrisburg, and Tea. He works with both buyers and sellers, guiding them from first search or listing all the way through closing.
Sources
- South Dakota DANR — Radon (Air Quality Program) — Zone 1 classification, 4 pCi/L action level, free test kits, average mitigation cost.
- EPA — Map of Radon Zones and EPA Radon home page — zone methodology and health guidance.
- South Dakota Searchlight (April 10, 2023) — American Lung Association data on SD’s elevated-test rate.
Tyce Ortman | eXp Realty 
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