Radon When Buying or Selling a Home in South Carolina

Updated October 2026 · 5 min read

Radon has a way of showing up late in a real estate deal: a buyer's inspection adds a radon test, the number comes back high and suddenly there are a few days to figure out what it means and who is paying. Knowing how it typically works in South Carolina takes most of the stress out of it, whether you are buying or selling.

This is general information, not legal advice. Your contract, your agent and, if needed, a real estate attorney are the right sources for your specific deal.

What South Carolina law requires

Disclosure of known radon

South Carolina's Residential Property Condition Disclosure Statement, in its current form effective June 1, 2023, asks sellers about known radon gas. If a seller knows about radon in the home, such as from a past test, that is the kind of thing the form is asking about.

No testing requirement

No South Carolina law requires a radon test before a home is sold. Sellers disclose what they know; they are not required to go find out. That puts the decision to test mostly in the buyer's hands.

Why radon comes up so often in Upstate deals

The Upstate has real radon. Greenville County is South Carolina's only EPA Radon Zone 1 county, and the other four Upstate counties are Zone 2. State test averages range from 1.7 pCi/L in Anderson County to 5.0 in Oconee County, and every county has recorded homes far above the EPA action level of 4 pCi/L. Many buyers and their agents know that and add a radon test to the inspection. For the numbers, see our county-by-county radon data.

For buyers: testing during your inspection period

Your purchase contract sets a window for inspections. A radon test needs to fit inside it, so schedule it early.

• Use a professional test. In a sale, results matter to two parties. A professional test with a continuous monitor and documented placement is harder to question than a kit set out by one side. A professional short-term test typically starts from about $150.
• Test the lowest lived-in level. That is a finished basement if one is used, otherwise the main floor.
• Closed-house conditions matter. Windows and exterior doors should be kept closed for 12 hours before and during a short-term test. If the house is vacant or being shown, ask your agent to coordinate with the seller's side.
• Plan for at least a couple of days. Short-term tests run 2 to 90 days; in a sale, the shortest workable window is typically used.

Our radon testing page explains how we run these tests.

If the result is 4 pCi/L or higher

The EPA recommends fixing a home at or above 4 pCi/L and considering it between 2 and 4. A high result is common and fixable. A radon mitigation system is a routine install, not a structural problem. What happens next is a negotiation, and these are the usual paths:

• Seller installs a system before closing. The buyer gets a working system and a post-install test showing the result.
• Seller gives a credit or price reduction. The buyer handles the install after closing and chooses the contractor.
• Costs are split. Some deals meet in the middle.
• Buyer takes it on. Sometimes the buyer simply decides to handle it.

Who pays is negotiable, and nothing in state law dictates the answer. Your agents will usually want a written estimate early so both sides are negotiating from a real number. Typical ranges in our area:

• Sub-slab depressurization (slab or basement): $900–$2,500
• Crawl space sub-membrane system: $1,500–$3,500
• Combination foundation: $2,200–$3,800

These are estimates; the final price comes after an on-site look. See the radon mitigation cost guide for what drives the number.

Timelines: what fits before closing

Every deal is different, but here is roughly how the pieces stack up:

1. Test

   A short-term test runs at least 2 days, plus time to set up closed-house conditions and get the report.

2. Estimate

   A site visit lets us see the foundation and plan the system, then we put the price in writing.

3. Install

   A typical install takes a few hours; more complex homes can take up to a day.

4. Retest

   A post-install test confirms the level came down. Build time for it into the schedule.

The tightest part is usually scheduling, not the work itself. The earlier the radon test is done in the inspection period, the more room everyone has.

For sellers: should you test before listing?

There is no legal requirement to test. But consider the tradeoffs:

• Testing first gives you control. If the level is high, you can fix it on your own schedule, choose your contractor and hand buyers a post-install result instead of a surprise.
• Know what you will need to disclose. Once you know about radon, the disclosure form asks about it. Talk to your agent about how to handle that.
• A working system with documentation reassures buyers. Many buyers are more comfortable with a house that has a system and a low post-install result than with one that has never been tested.

The paperwork that helps everyone

Whether you are the buyer or the seller, keep:

• The original radon test report, with dates and placement
• The written mitigation estimate and final invoice
• The post-mitigation test report
• A photo of the system label and the manometer, the gauge on the pipe that shows the fan is pulling suction

If you are buying a house that already has a system, ask for those documents and retest anyway. Fans are commonly replaced every 5 to 10 years, and a test is the only way to confirm a system is still doing its job. Our radon system repair page covers what we check on existing systems.

Bottom line

In South Carolina, radon in a home sale is mostly about information and timing. Sellers disclose what they know. Buyers decide whether to test. If the number is high, the fix is routine, and the only real question is who pays. Test early, get a written estimate quickly, retest after mitigation and keep the paperwork.

Frequently asked questions