Radon Testing in New Construction: What Homeowners and Builders Should Know

It is easy to assume a brand-new home is automatically safe. With radon, that assumption can backfire. New homes can still have elevated radon, and in some cases they can test higher than older homes because modern construction is often tighter and has less natural air leakage.

The good news is that new construction gives you a major advantage. It is the easiest time to include radon-resistant features, and it is often simpler to fix an elevated result when the home already has a radon rough-in or passive radon system installed. What matters most is doing the final step correctly: testing.

Why new homes still need radon testing

Radon is a naturally occurring radioactive gas that comes from the breakdown of uranium in soil and rock. It can enter a home through cracks and openings in the foundation, then build up indoors. You cannot see it, smell it, or taste it. Testing is the only way to know your level.

New construction does not eliminate the radon source. The soil under the home still produces radon. In addition, newer homes are often built with tighter envelopes, which can reduce air exchange and allow radon to accumulate more easily if it enters.

Another key point is variability. Radon can vary from house to house, even in the same neighborhood. That means “the development is new” is not meaningful protection. Your home must be tested as its own case.

Radon-resistant new construction and why it matters

Radon-resistant new construction (RRNC) refers to a set of building techniques designed to reduce radon entry and make it easier to lower radon levels if a problem is found. RRNC is often inexpensive compared to retrofitting later, especially when installed during construction.

RRNC typically includes features such as:

A gas-permeable layer under the slab (often gravel) to help soil gas move to a collection point
A plastic sheeting vapor barrier under the slab
Sealing and caulking at key openings and penetrations
A vent pipe (radon stack) that runs from beneath the slab up through the roof
An electrical rough-in near the vent pipe location so a fan can be added easily if needed

RRNC systems often start as “passive” systems, meaning they use natural pressure differences to vent soil gas. If radon still tests high, the system can often be upgraded to an “active” system by adding an in-line fan to create suction and improve performance.

What to ask your builder before you sign

If you are buying a new build, ask direct, specific questions. These questions also help you compare builders and avoid vague answers.

Were radon-resistant features installed?
Is there a passive radon system (a vent pipe from below the slab to the roof)?
Is there an electrical rough-in in place to add a fan if the home tests high?
Where is the suction point (or collection point) located?
What foundation type is the home (basement, slab, crawl space, or combination)?
Do you follow a specific RRNC standard or code requirement?
Has the home been tested already? If yes, when, where, and what were the results?

If the builder says “we built it radon resistant,” the follow-up question is: “Great, can you point to the vent pipe and show where the system routes and exhausts?” A real system is visible and traceable.

When should a new home be tested?

A simple rule is to test when the home is in normal, livable condition and you can control the test conditions.

Test right after moving in

If your home has a passive radon system, EPA guidance recommends testing immediately after moving in to make sure levels are below the guideline. This is especially important because if the home is already roughed-in for radon, upgrading to an active system is often straightforward if the result is elevated.

Consider a second test later for a stronger long-term picture

Radon can vary by season and building operation. Many homeowners run an initial short-term test for a fast answer, then follow up later with a long-term test for a better estimate of average exposure. This can be especially useful if the first result is near a decision threshold.

Test after major changes

Even in new construction, radon can change after:

Finishing a basement
Converting a basement to a bedroom or office
Major HVAC changes or ventilation upgrades
Foundation work or repairs

If the home changes, retesting removes guesswork.

Short-term vs long-term testing in a new home

New-home testing typically starts with a short-term test because it provides a quick answer. A short-term test can identify whether radon is likely elevated and whether action is needed.

Long-term testing is useful when:

You want the best estimate of your average exposure
Your short-term result is moderate or borderline
You want confirmation across different conditions and seasons

CDC guidance emphasizes testing before and after renovations and before lifestyle changes that increase time spent on lower levels, which applies well to new homes as they evolve.

How to test a new home correctly

Testing steps in a new home are similar to any home, but there are a few practical differences.

Step 1: Pick the correct level

Test on the lowest level that will be used regularly. If the basement will be a living space, test there. If the basement is unfinished and not used, test the first floor. If the home is slab-on-grade, test on the first floor.

Step 2: Choose a representative room

Use a room where people spend time, such as a family room, bedroom, or office. Avoid kitchens, bathrooms, laundry rooms, hallways, and closets unless a protocol specifically instructs otherwise.

Step 3: Follow closed-house conditions for short-term tests

Short-term tests often require windows and exterior doors to remain closed as much as possible, except for normal entry and exit. This creates a stable test environment and helps reduce misleading results caused by unusual ventilation.

Step 4: Do not test during unusual construction conditions

If contractors are coming and going constantly, doors are open for long periods, or major ventilation equipment is being installed or tested, your measurement may not reflect normal living conditions. If possible, test after the home is in normal occupied operation.

Step 5: Record and keep the result

Save results as part of your home documentation, especially for resale. A new home with radon testing history and clear documentation can be easier to sell and easier to evaluate for future changes.

What if your new home tests high?

If the result is at or above the EPA action level, the next step is not panic. The next step is a plan.

If you have a passive radon system

One of the biggest benefits of RRNC is that a passive system can often be upgraded by adding a fan. EPA guidance notes that if the radon level is at or above the guideline, a fan can often be installed to lower levels.

In practice, this upgrade usually involves:

Installing an in-line radon fan on the vent pipe
Ensuring the vent terminates properly above the roofline and away from openings
Checking system sealing and suction point effectiveness
Retesting to confirm the reduction

If you do not have radon-resistant features

Mitigation can still be installed after the fact, but it may require more work than a simple fan add-on. The most common approach in many homes is an active soil depressurization system. The exact design depends on the foundation type.

Retest after any fix

Any mitigation or system upgrade must be confirmed with a follow-up test. The fix is only real if the number drops.

Code and standards: what applies to new construction?

Radon requirements vary by state and locality. Some areas adopt radon-resistant construction requirements through building codes or local regulations. EPA maintains a reference page on building codes and standards that address RRNC. Industry standards also exist for rough-in components and radon control in new homes.

If you are building, you can ask the builder which standards or code provisions they follow. If you are buying, you can ask whether the home was built with radon-resistant features and whether the builder follows radon-related code guidance in your region.

A practical checklist for new-home buyers

Ask whether the home includes RRNC features and a passive radon system.
Confirm there is an electrical rough-in for a fan upgrade.
Test the home soon after moving in, especially if a passive system is installed.
If the result is elevated, upgrade to an active system and retest.
Retest after finishing a basement or changing how you use lower levels.
Keep your results for home records and resale documentation.

Bottom line

New construction does not eliminate radon risk. It simply gives you the best opportunity to build in radon resistance and make future fixes easier. The only way to know whether your new home has elevated radon is to test. If your home includes a passive radon system, testing immediately after moving in is smart, and upgrading to an active system is often straightforward if the result is high. If your home does not include radon-resistant features, mitigation is still possible, but it is typically easier and cheaper to include these features during construction.

Radon Testing in New Construction: What You Should Know