Most buyers and homeowners think of radon testing as a checkbox: order the canister, wait a few days, and move on. The decision that actually matters comes later, when the lab report shows a number above 4.0 picocuries per liter (pCi/L) and the house is suddenly a problem to solve. If your radon test came back high, the right next steps are not as urgent or as expensive as they sound. They do require a clear head and a short list of correct decisions, especially if you are still inside an inspection contingency window in Bucks, Montgomery, or Philadelphia counties.
This is the practical playbook our inspectors walk buyers and homeowners through when high radon test results show up in the Delaware Valley. Treat it as a starting point, not a substitute for a conversation with your real estate agent, your inspector, and a Pennsylvania-certified mitigation contractor.
What Counts As A High Radon Result?
The EPA uses 4.0 pCi/L as the action level for residential radon. At or above that level, the EPA recommends that homeowners install a mitigation system. Between 2.0 and 3.9 pCi/L, the EPA suggests considering mitigation, because there is no truly safe level of radon exposure, only a level low enough that the lung-cancer risk becomes small. Outdoor air typically averages around 0.4 pCi/L, which is the practical floor most homes can reach with a properly designed system.
Local context matters. Bucks and Montgomery counties sit on the Reading Prong, a uranium-rich geological feature that runs through Southeastern Pennsylvania. The Pennsylvania Department of Environmental Protection has documented some of the highest residential radon readings in the country in this region. A first-time buyer in Doylestown or Abington seeing a 6 or 7 pCi/L result is not unusual, even in a well-maintained home with a finished basement. The number is not a verdict on the house. It is a measurement of the soil gas underneath it and how that gas moves through the foundation.
How To Read The Lab Number In Context
One number on its own does not tell the full story. Three details from the test report determine how to act:
- Test type and duration. A short-term test (2 to 7 days) shows a snapshot. A long-term test (90 days or more) shows the average a household actually breathes year round. Both are valid; they answer different questions.
- Closed-house conditions. Radon test protocols require windows and exterior doors closed except for normal entry and exit during the test. A test taken with windows open or with strong ventilation running will read low and is not reliable.
- Where in the home it was placed. The canister belongs in the lowest livable level. If a basement is used as a finished den, gym, or guest space, the basement reading is the right number to act on.
Should You Retest Before You Mitigate?
Retesting is sometimes the right call and sometimes a delay tactic. The decision depends on how high the first result came back and how the test was conducted. As a working rule:
- Result above 8 pCi/L. Most professionals act on the first result. The EPA recommends mitigation, and additional confirmation testing rarely changes the decision.
- Result between 4 and 8 pCi/L. A confirmation test is reasonable, especially if conditions during the first test were not ideal (windows opened, HVAC tuned to outside-air mode, severe weather shifts).
- Result between 2 and 3.9 pCi/L. Decide based on how the home is used. A finished basement bedroom or full-time home office at 3 pCi/L is a different calculus than a rarely used storage basement at the same number.
If you do retest, follow the same closed-house protocol and use the lowest livable level. A continuous radon monitor (CRM) gives an hour-by-hour read and can show whether weather, HVAC cycling, or open windows are skewing the number. CRMs are most often used by professional testers; a homeowner short-term canister kit is fine for confirmation if used correctly. For a refresher on test mechanics, see our post on how long a radon test takes.
One caveat for buyers under contract: do not let a retest push you outside your inspection contingency window without a written extension. The clock keeps running while the second canister sits in the basement.
How Does Radon Mitigation Actually Work?
Mitigation is not a chemical treatment, an air purifier, or a sealing job. Modern residential radon mitigation removes the gas from underneath the foundation before it can enter the home, and it works.
Sub-Slab Depressurization
The most common system in Pennsylvania is sub-slab depressurization. A contractor drills through the basement slab, installs a suction pit, runs a sealed PVC pipe up through the home (or up the exterior), and adds an inline radon fan. The fan creates negative pressure under the slab so radon-laden soil gas vents above the roofline instead of into the living space. A correctly designed system typically pulls indoor radon down to between 0.5 and 2.0 pCi/L, often lower.
Crawl Space And Slab-On-Grade Variants
Homes with crawl spaces use a sub-membrane system: a heavy polyethylene sheet is sealed across the crawl space floor, the suction line is run under the membrane, and the same fan-and-vent stack carries the gas out. Slab-on-grade homes use sub-slab suction with the suction point selected to match the slab layout. Older Bucks and Montgomery homes with a mix of full basement, crawl, and addition slabs sometimes need two suction points to achieve a uniform draw across the foundation.
Cost, Timeline, And Who Should Do The Work
For a typical single-family home in Southeastern Pennsylvania, a residential mitigation system runs in the low-to-mid four figures, installed in one working day. Complex foundations, two-fan systems, or aesthetic upgrades (interior chase rather than exterior pipe) push the cost higher. Pennsylvania law requires that anyone offering mitigation services for compensation be certified by the Pennsylvania Department of Environmental Protection. Verify the certification number before signing a proposal. After the system is installed, plan on a post-mitigation test 24 hours to 30 days later to confirm the new average reading.
How Should A High Result Affect The Sale?
If the high result came from radon testing run as part of a buyer’s home inspection, the report becomes a negotiation document. The right move depends on the contract, the contingency window, and how the seller has handled inspection findings up to that point.
Buyer Options Inside The Contingency Window
- Request mitigation before closing. Most common in Bucks, Montgomery, and Philadelphia. The seller hires a certified mitigation contractor, the system is installed, a post-mitigation test confirms levels below 4 pCi/L, and proof is provided at closing.
- Request a credit at closing. The buyer accepts the home with the existing condition and is credited for the mitigation cost. This is faster but puts the install on the buyer’s calendar after move-in.
- Request a price reduction. Functionally similar to a credit, structured differently for loan and tax reasons. Have the buyer’s agent and lender confirm what the mortgage allows.
- Terminate the contract. Allowed during an active inspection contingency window. This is rarely the correct choice for a radon-only finding, because mitigation is a known, finite, and effective fix.
If A Mitigation System Is Already In Place
Some homes already have a system installed, especially in Bucks and Montgomery. A working system is a feature, not a flag. Confirm three things before you accept it: the fan is running and shows a meaningful pressure reading on the manometer (the U-tube gauge on the pipe), the most recent post-mitigation test result is on file or available from the seller, and the system was installed by a Pennsylvania-certified contractor. If any of those are missing, request a fresh radon test on the lowest livable level before closing.
Sellers, Pre-Listing Tests, And Disclosure
Sellers in the Delaware Valley sometimes ask whether to run a radon test before listing. The trade-off is real. A pre-listing high reading must be disclosed under Pennsylvania’s Real Estate Seller Disclosure Law, but pre-listing mitigation also lets the seller control the contractor, the cost, and the timeline rather than negotiating in a 7 to 10 day window with a stranger’s lender on the other side. For homes in known high-radon areas, owning the result early is usually the calmer path. We touch on related sequencing in our guide to scheduling a home inspection.
Frequently Asked Questions About High Radon Results
Is 4 pCi/L truly the safe cutoff?
4 pCi/L is the EPA action level, not a biological threshold for safety. The EPA itself notes that there is no known safe level of radon and recommends considering mitigation between 2 and 4 pCi/L. The 4 pCi/L number reflects what mitigation systems can reliably and affordably achieve in residential construction.
Can radon levels change over time in the same house?
Yes. Radon readings can shift with seasons, frost depth, soil moisture, foundation cracking, HVAC changes, and even barometric pressure. A home that tested at 2.5 pCi/L five years ago can read 6.0 pCi/L today, and the reverse is also possible. The EPA recommends retesting every two years and after any major foundation, HVAC, or basement-finishing work.
Does a finished basement make radon worse?
Finishing a basement does not create radon, but it does usually mean people are spending more hours on the lowest level of the home, which raises the practical exposure. If a basement is going to be a bedroom, gym, or full-time office, target levels well below 4 pCi/L and consider mitigation even at borderline numbers.
Will a mitigation system hurt the home’s resale value?
In high-radon regions like Bucks and Montgomery counties, an installed and verified system tends to be a neutral-to-positive feature, especially with a recent post-mitigation test on file. It removes a recurring negotiation point for future buyers.
Can a homeowner install a radon mitigation system DIY?
Anyone offering radon mitigation services in Pennsylvania for compensation must be certified by the PA Department of Environmental Protection. Homeowners performing work on their own home are not subject to the certification requirement, but design errors are common in DIY installs (wrong suction location, undersized fan, improper roof termination, no manometer). The cost difference rarely justifies the risk of building a system that does not actually pull the level below 4 pCi/L.
How often should I retest after a mitigation system is installed?
Run a post-mitigation test within 24 hours to 30 days of activation to confirm the system is performing. After that, the EPA recommends retesting every two years and any time the system fan stops, the manometer reading goes flat, or major work is done on the basement, foundation, or HVAC.
Does homeowner’s insurance cover radon mitigation?
Standard homeowner’s insurance policies in Pennsylvania generally do not cover radon testing or mitigation; radon is treated as a maintenance and disclosure issue rather than a sudden insurable loss. Policies vary, so check with your carrier directly.
Next Steps If Your Result Came Back High
A high radon test result is a number, not a crisis. The right sequence is almost always the same: confirm the result if anything about the test conditions was unusual, hire a Pennsylvania-certified mitigation contractor, install the system, and run a post-mitigation test to verify the new level. If the test was part of a real estate transaction, work the result into the inspection contingency before the window closes. If you are a homeowner who simply wanted to know, the same playbook applies on a calmer timeline.
Inspection Professionals provides residential radon testing for buyers, sellers, and homeowners across Bucks County, Montgomery County, and Philadelphia. If you need a baseline test, a confirmation test, or a post-mitigation verification, schedule a radon test with our office and we will fit it into your inspection or transaction timeline.