Radon and mold testing in a home inspection: what buyers should know

Here is the short answer: a standard home inspection does not test for radon or mold. Both are "add-on" tests a buyer has to request separately, and both matter a lot for health and safety. The EPA says radon is the second leading cause of lung cancer in the United States, causing about 21,000 deaths a year, so it is worth the extra step. This guide walks you through what each test covers, what it costs, and what to do with the results before you sign anything.

We wrote this for home buyers, but inspectors will find it useful too. It explains why these two tests live outside a normal inspection, how they actually work, and how a smart, voice-driven inspection workflow like PadInspector can help an inspector flag a concern on the spot so nothing gets forgotten before closing.

What is radon, and why does it show up in home inspections?

Radon is a gas you cannot see or smell. It comes up from the ground and seeps into homes through cracks in the foundation. It forms naturally when uranium in soil and rock breaks down. Every home can have it, no matter how new, old, fancy, or plain.

The tricky part is that radon builds up indoors, especially in basements and lower floors, and you would never know it was there without a test. That is exactly why buyers ask for radon testing during a home purchase.

What is mold, and why does it show up in home inspections?

Mold is a type of fungus. It grows almost anywhere there is moisture: bathrooms, basements, attics, and around leaky windows or pipes. Tiny mold spores float in the air all the time, and they only turn into a problem when they land somewhere damp and start to grow.

The EPA's guide to mold and moisture puts it simply: moisture control is mold control. No water, no mold growth. That is why a musty smell or a water stain on a ceiling is worth a second look before you buy.

Radon versus mold at a glance

The two tests get lumped together, but they look for very different things. Here is how they compare on what they are, how they are checked, and what they cost.

Factor	Radon	Mold
What it is	An invisible radioactive gas that seeps up from the soil	A fungus that grows on damp surfaces indoors
How it is tested	A monitor in the lowest lived-in level for a set number of days	A visual check plus moisture meters and air or surface lab samples
Typical cost	Testing is cheap; mitigation runs close to the cost of a typical home repair	A dedicated inspection with lab samples commonly runs a few hundred dollars
Action point	Mitigate at or above 4 pCi/L	Call a specialist above about 10 square feet or a persistent musty smell

Does a standard home inspection include radon or mold testing?

No, not usually. A general home inspection checks the big systems: roof, foundation, plumbing, electrical, heating, and cooling. Radon and mold testing are specialized add-ons that a buyer has to ask for and often pay for separately.

What does the ASHI Standard of Practice say about radon and mold?

The ASHI Standard of Practice, the rulebook many inspectors follow, spells this out directly. It states inspectors are not required to determine "the presence of environmental hazards including, but not limited to, allergens, toxins, carcinogens, electromagnetic radiation, noise, radioactive substances, and contaminants in building materials, soil, water, and air." It also excludes "mold and mold-like substances" from the standard scope. In plain words, your general inspector can flag a suspicious stain or a strange smell, but a full radon or mold test needs a separate service.

How does radon testing actually work during a home purchase?

Radon testing is simple, cheap, and fast compared to the risk it can catch. A small monitor sits in the lowest lived-in level of the home, usually the basement, for a set number of days while doors and windows stay mostly closed.

Short-term test versus long-term test

Per the CDC's radon testing guidance, a short-term test runs for 2 to 90 days and gives you a quick snapshot. A long-term test runs for more than 90 days and shows the home's true year-round average, since radon levels shift with the seasons. Most real estate deals use a short-term test because closings move fast, but a long-term test gives a more complete picture if you have the time.

What counts as a safe radon level?

The EPA's action level is 4 picocuries per liter of air, often written as 4 pCi/L. At or above that number, the EPA recommends fixing the home with a mitigation system. Even levels between 2 and 4 pCi/L are worth a second look, since there is no fully "safe" amount of radon, only lower risk.

What happens if the radon test comes back high?

Do not panic. Radon is one of the most fixable problems a home can have. The CDC explains that most homes use a vent pipe and fan system that pulls radon from under the house and blows it safely outside. This kind of system does not require major construction, and most homes can be fixed for close to the cost of a typical home repair. Buyers often negotiate with the seller to install this system before closing.

How does mold testing actually work during a home purchase?

Mold testing looks a little different from radon testing because mold is often something you can see or smell before you ever test for it. A visible fuzzy patch, a musty basement smell, or a water stain on drywall are all signs worth checking out.

When should a buyer call in a mold professional?

Bring in a specialist if any of these apply:

• You see mold covering more than about 10 square feet.
• More than one room smells musty.
• Someone in the household has ongoing breathing trouble.
• The home had a recent leak, flood, or burst pipe.

A trained mold inspector uses moisture meters and sometimes a thermal camera to find damp spots hiding behind walls, then takes air or surface samples to a lab.

What does mold testing usually cost?

A dedicated mold inspection with lab samples commonly runs a few hundred dollars, depending on the size of the home and how many samples the lab needs to run. That is a small price compared to the cost of removing hidden mold damage after you already own the home.

What health risks come with radon and mold?

Both radon and mold are silent problems. They rarely make a home look bad from the curb, but they can affect the people living inside it for years.

Radon and lung health

Radon breaks down into tiny radioactive particles that can lodge in lung tissue when you breathe them in. Over years of exposure, this raises the risk of lung cancer. According to the National Association of Realtors, about 1 in 15 U.S. homes has an elevated radon level, and radon causes roughly 20,000 lung cancer deaths every year. Smokers face an even higher combined risk when radon is also present.

Mold and everyday health

Mold exposure affects people differently. The CDC notes that damp, moldy environments can cause a stuffy nose, sore throat, coughing, wheezing, and skin irritation. People with asthma or a mold allergy can have stronger reactions, and those with weak immune systems or chronic lung disease face a higher risk of lung infection. Kids who are genetically prone to asthma may be more likely to develop it after early mold exposure.

Who should pay for testing, the buyer or the seller?

There is no single rule, and it often comes down to negotiation. Many sellers test ahead of time and share the results as part of their disclosures, especially since most real estate radon testing happens as part of the buyer's home inspection anyway. Other times the buyer pays for the test as one more line item alongside the general inspection. Either way, get it in writing who is covering the cost before the test happens, so there is no confusion at closing.

What should you do if radon or mold shows up before closing?

A bad result is a starting point for negotiation, not a reason to run. Work through it in three steps:

• Do not walk away from a good house over a fixable problem. Radon mitigation systems and mold remediation are both common, well-understood repairs that licensed contractors handle every day.
• Use the result as a negotiating tool. Many buyers ask the seller to pay for the fix, lower the price to cover it, or complete the repair before closing.
• Always retest after any fix. A radon system should bring levels below 4 pCi/L, and a mold remediation job should come with a clearance test showing the problem is actually gone, not just painted over.

How PadInspector helps with radon and mold documentation

PadInspector will not run the lab test for you, since radon and mold sampling need certified equipment and, often, a separate license. What it does is make sure nothing about a suspicious stain, smell, or crack gets lost between the walkthrough and the final report. As you walk the home and talk, PadInspector transcribes your notes and automatically attaches your photos to the right area, so a damp basement corner or a hairline foundation crack is documented with a note and a picture in the same spot, not scattered across your phone's camera roll.

It also looks up building-code violations automatically as you go, which helps catch related issues, like poor grading or missing vapor barriers, that often go hand in hand with moisture and radon risk. Because it logs the weather on inspection day, you also have a record showing conditions at the time, which matters if a buyer later asks why a moisture issue was not obvious that day. Check the full PadInspector feature list to see how voice-driven notes, photo tagging, and code lookups work together in one report.

PadInspector is invite-only while the team grows carefully and keeps client data private and secure. If you want your inspection reports finished before you leave the driveway, with every defect, photo, and code reference already in place, request an invite today.

FAQ: radon and mold testing in home inspections

Is radon testing required to buy a house?

No, it is not required in most places, but it is strongly recommended. The EPA, CDC, and most state health departments suggest every buyer test for radon before closing, since it is cheap, fast, and radon is impossible to detect without a test.

Does a home inspector automatically check for mold?

Not as a rule. A general home inspector may point out a visible stain or musty smell as a courtesy, but full mold testing and sampling are a separate, specialized service under standards like the ASHI Standard of Practice.

How long does a radon test take?

A short-term test usually takes 2 to 90 days, and most real estate deals use one on the shorter end of that range so results come back before closing. A long-term test runs more than 90 days and shows a more accurate year-round average.

What radon level should worry a buyer?

The EPA's action level is 4 picocuries per liter of air. At or above that number, a mitigation system is recommended. Levels between 2 and 4 pCi/L are also worth discussing, since lower is always safer.

Can a house with mold or high radon still be a good buy?

Yes, in most cases. Radon mitigation systems and mold remediation are common, affordable repairs. Many buyers negotiate the cost into the deal rather than walking away from an otherwise good home.

Who usually pays for radon or mold testing, the buyer or seller?

It varies by deal. Sellers sometimes test ahead of time and disclose results, while other times the buyer requests and pays for the test alongside their general home inspection. Put the arrangement in writing before the test happens.

Should I retest after a radon or mold fix?

Yes, always. A radon mitigation system should be retested to confirm levels are below 4 pCi/L, and mold remediation should end with a clearance test showing the mold is actually gone.