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Why Radon Mitigation Before Closing Can Save Your St. Louis Home Sale

If you are buying or selling a home in St. Louis, you have probably heard about radon. It is a radioactive gas that comes from the natural decay of uranium in the soil. It can seep into any building through cracks in the foundation, gaps around pipes, or even through the slab itself. The thing is, radon is not something you can see or smell. The only way to know if it is present is to perform a radon test. And if the test comes back high, you have a decision to make. Do you walk away from the deal? Do you ask for a credit? Or do you negotiate for a radon mitigation system to be installed before you close? That last option, radon mitigation before closing, is becoming more common in the St. Louis market. And for good reason.

When I first started working in home radon testing, most buyers just wanted to know if the house had a problem. If the radon level was above the EPA action level of 4.0 picocuries per liter, they would often just ask for a price reduction and deal with it later. But over the years, I have seen a shift. More buyers are insisting that a mitigation contractor install a system before the closing process is complete. They want the problem fixed, not just a discount. And sellers are starting to realize that offering to handle radon mitigation before closing can actually make their property more attractive.

What Happens When a Radon Test Comes Back High?

Let's walk through a typical scenario. A buyer puts an offer on a house in the St. Louis area. The home inspection goes well. The roof is solid, the HVAC system is in good shape, and the foundation looks sound. But the buyer's agent recommends a radon test as a buyer contingency. So we set up a continuous radon monitor, or CRM, in the lowest livable level of the home. A CRM is different from a short-term radon test because it takes readings every hour over a few days. It gives a much more accurate picture of the average radon level. After three days, the result comes back at 6.8 picocuries per liter. That is well above the EPA action level.

Now the buyer has a choice. Some states require a radon disclosure from the seller, but Missouri does not have a state-wide seller disclosure law for radon. That means the seller might not have known about the problem. But once the test is done, everyone knows. The buyer can back out, ask for a credit, or negotiate for a mitigation system. More and more, I see buyers choosing to handle radon mitigation before closing. They want the system installed and verified before they sign the final papers. This is where a good mitigation contractor comes in.

The Practical Side of Installing a Mitigation System

A typical radon mitigation system involves a fan and a pipe that pulls the gas from beneath the foundation and vents it above the roofline. It is not a huge construction project. In many cases, it can be installed in a day. But there are factors that can slow things down. The type of foundation matters. A basement with a sump pump or a crawl space with a dirt floor will require different approaches. The contractor needs to seal any foundation cracks and ensure the system is pulling from the right spot. After installation, a follow-up radon test is needed to confirm the system is working. That follow-up test usually takes another three days with a CRM.

So if you are trying to schedule radon mitigation before closing, you need to leave enough time. I have seen deals get pushed back because the buyer and seller did not plan for the testing window. If the closing is in two weeks, that might not be enough time to get the system installed, tested, and verified. The smart move is to start the radon test early in the home inspection period. That way, if the level is high, you have room to negotiate and install without scrambling.

Who Pays and Who Chooses the Contractor?

This is where things get a little tricky. In my experience, the cost of the mitigation system usually falls on the seller. After all, it is their house, and a high radon level is a defect that needs to be fixed before the buyer will take ownership. But sometimes the buyer will agree to split the cost if the seller is already stretched thin. What matters most is that both parties agree on a qualified mitigation contractor. You do not want a handyman who has never installed a radon system before. You want someone who knows how to size the fan, seal the penetrations, and avoid creating negative pressure issues with the HVAC system.

Air Sense Environmental does not install mitigation systems, but we work closely with several trusted contractors in the area. When a client asks for a recommendation, we can point them to someone who has a track record of doing the job right. And we always recommend that the buyer get a radon test after the system is installed. That way, the buyer knows the radon level is below the action level before they move in. This is a key step in any real estate transaction where radon has come up.

Is It Better to Ask for a Credit Instead?

Some buyers prefer to ask for a credit at closing and then handle the mitigation themselves. That can work, but it has risks. For one thing, the buyer might not realize how much the system will actually cost. A typical radon mitigation system runs between $800 and $2,500 depending on the complexity of the job. If the buyer asks for a $1,000 credit and the system costs $2,000, they are left paying the difference. Also, the buyer might not get around to installing the system right away. They move in, get busy with other things, and the radon problem lingers. That is not good for anyone's health.

On the other hand, handling radon mitigation before closing puts the pressure on the seller to get it done quickly and correctly. The seller has an incentive to close the deal, so they are more likely to move fast. And the buyer gets the peace of mind of knowing the house is safe from day one. I have seen a few deals where the buyer took a credit, moved in, and then discovered that the radon level was still high after they installed a cheap system. They ended up spending more money to fix it again. So in most cases, I recommend that buyers push for the system to be installed before the closing process is finalized.

The Role of Continuous Radon Monitors in the Process

I mentioned CRMs earlier, and I want to expand on that because they make a real difference. A short-term radon test, like a charcoal canister, gives you a single result after two to seven days. But it can be thrown off by short spikes in radon levels. A CRM records readings every hour and gives an average that is much more reliable. In a real estate transaction, using a CRM means fewer disputes over the result. If the buyer and seller both see the hourly data, they trust the outcome. And when it comes time to verify the mitigation system, a CRM is the best tool for the job. You can see if the system is keeping the radon level consistently low, not just on one day.

This is especially important in St. Louis because our geology is varied. Some neighborhoods have very high radon potential, while others are lower. A CRM helps you get a clear picture no matter where the house is located. And if you are dealing with a seller who is skeptical about the initial test, showing them the hourly data from a CRM can help move the conversation forward.

What About Radon Resistant Construction in Newer Homes?

You might think that a newer home is automatically safe from radon. That is not always true. Radon resistant construction techniques, like placing a layer of gravel under the slab and running a vent pipe up through the roof, are code in many areas now. But those systems are passive. They rely on natural air pressure differences to draw the gas out. Sometimes they work, and sometimes they don't. If a passive system is in place, a radon test can tell you if it is performing well. If the test comes back high, you can usually add an active fan to turn it into an active radon mitigation system. So even in a newer home, it is worth testing and considering radon mitigation before closing if the numbers are high.

Practical Tips for Buyers and Sellers

If you are a buyer, here are a few things to keep in mind:

  • Include a radon test as a buyer contingency in your offer. Do not skip it just because the house looks clean.
  • If the test comes back above the action level, ask for radon mitigation before closing rather than a credit.
  • Make sure the mitigation contractor is licensed and experienced. Ask for references if you need to.
  • Insist on a follow-up test using a CRM to verify the system is working before you close.
  • Work with a company like Air Sense Environmental that uses continuous monitors for accurate results.

If you are a seller, consider this: offering to handle radon mitigation before closing can make your house stand out. Buyers appreciate not having to deal with the hassle after they move in. And if you already know the house has high radon, getting it fixed before you list can prevent surprises later. A pre-listing radon test can tell you where you stand, and if the level is high, you can install the system and retest before the buyer even walks through the door. That makes the transaction smoother for everyone.

Final Thoughts on Moving Forward

Radon is a real concern in St. Louis, but it does not have to stop a home sale. With a little planning and the right approach, you can handle it in a way that protects your health and your investment. Whether you are a buyer who wants a safe home or a seller who wants a clean closing, addressing the issue upfront is the smartest path. I have seen too many deals get complicated because someone waited until the last minute. A little foresight goes a long way. And if you find yourself in a situation where the radon level is high, remember that radon mitigation before closing is not just a fix. It is a solution that lets everyone move forward with confidence.