The short answer
Test. EPA’s map puts Wake County in its moderate radon potential zone, and EPA says all homes should be tested regardless of zone. The NC Radon Program adds that homes on crawl spaces need testing too. For Wake County, it recommends testing indoor air every 2 years, considering mitigation at 2 to 3.9 pCi/L, and strongly recommends hiring a certified radon professional at 4.0 pCi/L or higher. If you’re closing your crawl space, test before and after.
Where radon comes from
NC’s Wake County radon fact sheet explains that radon is a gas naturally present in rocks and soil in North Carolina, created when uranium in the ground decays; it can’t be seen, smelled or tasted, and testing the air is the only way to know whether it’s getting indoors. The same fact sheet says radon can be harmful and cause lung cancer if it builds up in the air you breathe.
A crawl space sits directly on that soil. Whether radon reaches the rooms above depends on the soil, the house’s air pressure, and how well the floor separates the crawl space from the living space.
Wake County’s numbers
| Measure | Wake County | Source |
|---|---|---|
| EPA radon map classification | Zone 2 EPA radon zone (moderate potential) | EPA Map of Radon Zones |
| Average in the state’s school radon survey | 1.5 pCi/L average | NC Radon Program |
| Level at which the NC Radon Program suggests considering mitigation | 2 to 3.9 pCi/L | Wake County fact sheet |
| Level at which it strongly recommends mitigation | 4.0 pCi/L or higher | Wake County fact sheet |
| How often to test indoor air | Every 2 years | Wake County fact sheet |
A county zone and a school average describe the area, not your house. Two neighboring houses can test very differently, which is why the advice is to test every home.
What closing a crawl space does to radon
Advanced Energy measured radon in its Princeville study houses, which had either vented or closed crawl spaces. Long-term readings in the crawl spaces themselves averaged slightly higher in the closed ones: 1.1 vs 0.5 pCi/L, closed against vented. In the living spaces there was no difference tied to foundation type; all the houses averaged about 0.5 pCi/L.
That’s one study of 12 homes in eastern North Carolina, with low readings throughout. It suggests closing a crawl space doesn’t automatically raise radon upstairs, but it can’t tell you what will happen in your house. So:
- Test before the work, to know your starting point.
- Test again after, once the crawl space has been closed and the drying method has run for a while.
- If the result is high, talk to a certified radon professional about mitigation before or alongside the encapsulation. In a crawl space house, the radon system and the sealed liner can be planned together rather than one tearing into the other.
How to test
The NC Radon Program recommends that every home be tested, and says you can buy a test kit or hire a certified radon professional. A few practical points:
- Test in the lowest lived-in level of the house, following the kit’s instructions.
- Keep windows and doors closed as the instructions direct.
- If one short test comes back high, follow up with a second test or a longer one before deciding on mitigation.
- With a mitigation system in place, keep testing: the program recommends testing at least every five years, whether or not you have a system.
Buying or selling
A radon test fits naturally into a buyer’s due diligence alongside the home inspection, and a seller with recent results and any mitigation records can answer the question before it’s asked. The guide to selling or buying with crawl space problems covers the rest of the paperwork.
Radon testing and mitigation are their own trade. A crawl space contractor can tell you how a closed crawl space is built; a certified radon professional can tell you what your house’s radon level means and how to bring it down.
Want a contractor to look at it? Call to schedule an inspection.