Radon in Northern Virginia Homes: Testing, Results and Fixes

Radon is a natural radioactive gas that comes from uranium in soil and rock. It can seep into homes through foundation cracks and gaps. You can’t see or smell it, and long-term exposure is a leading cause of lung cancer after smoking. The good news: it’s easy to test and usually straightforward to fix.

How common is radon here?

The Fairfax County Health Department says homes in the county are at high risk, and the EPA rates Fairfax as Zone 1. The Virginia Department of Health says Loudoun should be considered high risk as well. Radon levels vary from house to house, even on the same street. The EPA and the Virginia Department of Health recommend testing all homes, especially homes being purchased.

Testing during a home purchase

Test type	How it works	Best for
Short-term test	A device runs for at least 48 hours with windows and doors closed	Home purchases, because results come fast
Continuous monitor	An electronic monitor records hourly levels	Real estate transactions, with tamper detection
Long-term test	Runs 90 days or more	Owners who want a year-round picture

Most buyers order a radon test with their home inspection. Results come back within a few days, inside a typical inspection contingency period. See my home inspection guide for how to fit it into your timeline.

Reading the result

Result	What it means
Below 2 pCi/L	Low. No action needed.
2 to 3.9 pCi/L	Below the EPA action level, but the EPA suggests considering mitigation.
4 pCi/L or higher	At or above the EPA action level. Mitigation is recommended.

What mitigation involves

The most common fix is sub-slab depressurization. A contractor drills through the basement slab, installs a pipe and runs it up and out of the house with a fan that pulls radon from under the foundation before it enters. Sealing cracks helps too. After installation, the home should be retested to confirm levels dropped.

A worked example: negotiating a high result

Say you’re buying a $700,000 home in Fairfax and the test comes back at 6.2 pCi/L. You get a mitigation quote and ask the seller to install a system with a passing retest before closing, or to give a credit for the quoted amount. Either way, the problem is solved for a small fraction of the price, and you know the system is there when you sell later. For tips on how to ask, read negotiating repairs after inspection.

Radon and new construction

Some builders install passive radon pipes in new homes, which can be upgraded with a fan if a test shows high levels. If you buy new, ask whether the home has a radon-resistant design, and test after you move in.

Selling a home in a high radon area

If you plan to sell, consider testing before you list. A known, mitigated result with a passing retest removes a common inspection surprise and makes negotiations smoother. Keep the installer’s paperwork and the retest results to share with buyers.

Common mistakes

• Skipping the test because the house “has a mitigation system.” Retest to make sure it works.
• Opening windows during a test, which skews results.
• Assuming a home without a basement is safe. Slab and crawl space homes can have radon too.
• Not checking the fan. Mitigation fans run all the time and can wear out.

Radon zone status is also one of the items on Virginia’s disclosure form, though it mostly tells buyers to check for themselves. Learn more in Virginia seller disclosures explained.

Frequently asked questions

Can I test for radon myself?

Yes. Kits are sold at hardware stores, and the Virginia Department of Health offers low-cost kits. For a home purchase, most buyers hire a professional for faster, documented results.

Does a radon system hurt resale?

Generally no. In high-radon areas, many buyers see an installed, working system as a plus.

Should I retest after moving in?

It’s a good idea to retest every few years and after major renovations, especially if you finish a basement.