Radon Gas in Homes: What Homeowners Need to Know
Radon gas in homes is the single largest source of radiation exposure for most people, and it enters through the ground beneath the foundation rather than from anything inside the house. It is invisible, odorless, and tasteless, which is why so many homes with elevated levels go undetected for years. Colorado’s geology makes the Front Range especially prone to high readings. This guide explains how radon gets into a home, why it concentrates where it does, what level is unsafe, and how homeowners measure and reduce it. This guide summarizes EPA and Colorado state guidance current as of 2026 and is educational only; consult your physician about health concerns and a certified professional for testing decisions.
How radon gas gets into homes
Radon forms underground from the natural radioactive decay of uranium in soil and rock. As it breaks down, it produces radon gas that migrates up through soil and enters a home through the path of least resistance: cracks in the foundation slab, gaps around pipe penetrations, sump pits, crawl space floors, and joints between the slab and walls. A house effectively acts like a chimney, with warm indoor air rising and drawing soil gas in from below through a slight pressure difference.
Because the source is the ground, even a brand-new, well-built home can have high radon. Construction quality affects how much enters, but it does not eliminate the source. The full picture of radon’s geological origin is covered in where radon comes from, and the overall homeowner framework is in the radon testing guide.
Water from private wells can be a secondary source in some areas, releasing dissolved radon into indoor air during showering and other use, though soil gas is the dominant pathway for most homes.
Why basements concentrate radon
Radon levels are typically highest in the lowest occupied level of a home because that space is in closest contact with the soil and experiences the strongest pressure-driven entry. Basements and slab-on-grade lower floors therefore tend to read higher than upper stories. Finishing a basement into living space turns a low-occupancy zone into a daily-use one, which raises the relevance of the reading there.
This is why testing is usually performed in the lowest livable level. The reasons radon accumulates below grade, and what that means for finished basements, are detailed in radon in the basement. Front Range homes with finished basements are a common scenario where a test is especially worthwhile.
How seasons and habits affect levels
Indoor radon fluctuates. Levels often run higher in winter, when homes are sealed and heating systems increase the pressure difference that draws soil gas inward. Closed windows, certain ventilation patterns, and changes in soil moisture all shift readings, which is why a single short measurement is a snapshot rather than a definitive annual average.
Day-to-day habits matter too. Running exhaust fans, using a fireplace, or operating certain HVAC configurations can change the pressure balance and nudge radon entry up or down. Heavy rain or snowmelt that saturates the surrounding soil can cap the ground and temporarily push more gas toward the house’s foundation. None of this changes the recommendation to test; it explains why a short-term test should be conducted under closed-house conditions and why an elevated result is often confirmed before mitigation.
The health risk of radon in homes
The EPA identifies radon as the second-leading cause of lung cancer overall and the leading cause among people who have never smoked. The risk comes from inhaling radon decay products, which lodge in lung tissue and emit radiation over time. The danger is cumulative and long-term; there are no immediate symptoms, which is part of what makes radon hazardous. Smokers face a substantially higher combined risk.
Because the harm is cumulative and silent, the only protection is measurement and reduction. There is no acute illness to warn a household, a point explained further in the discussion of the first signs of radon poisoning, which clarifies why “symptoms” are not a reliable indicator.
The risk scales with both concentration and time. Living for years in a home at 8 pCi/L carries more cumulative exposure than a short stay at the same level, which is why the duration of occupancy and the time spent in lower-level rooms factor into how seriously a household should treat a result. The EPA frames the risk in comparison to other familiar hazards, noting that radon at elevated levels contributes a meaningful share of lung-cancer cases each year, with the danger amplified for current and former smokers.
Testing for radon gas in homes
Testing is straightforward and inexpensive. Short-term test kits measure over two to seven days and give a quick screen, while long-term kits measure over 90 days or more for a better annual estimate. Continuous electronic monitors provide ongoing readings. The EPA recommends testing the lowest lived-in level and acting at or above 4 pCi/L.
Because levels vary, an elevated short-term result is often confirmed with a follow-up test before committing to mitigation. The differences among methods and how to interpret pCi/L readings are covered in the radon test guide and the radon levels chart. For Colorado homes, where elevated results are common, testing is the prudent default for every property.
Reducing radon in a home
When a home tests at or above 4 pCi/L, mitigation reliably lowers it. The most common method is sub-slab depressurization: a pipe and an inline fan draw soil gas from beneath the foundation and vent it above the roofline before it can enter the living space. Sealing visible cracks supports the system but is not a standalone fix. Professionally installed systems routinely bring levels well below the action threshold.
Most residential mitigation systems fall in the range of roughly $800 to $2,500 installed, depending on the home’s foundation and layout. The process and what to expect are described in the radon remediation guide. Homeowners with elevated readings should consult a certified mitigation professional rather than relying on partial do-it-yourself sealing.
Radon and the Colorado Front Range
Colorado consistently ranks among the highest-radon states, and the Front Range is squarely within that pattern. The region’s soils contain uranium that decays into radon, and the state health department maps elevated potential across Denver, Douglas, Jefferson, Arapahoe, Boulder, Adams, Broomfield, and El Paso counties. A large share of homes tested in these areas come back above the 4 pCi/L action level, making radon a routine consideration rather than a rare one.
This prevalence shapes practical advice for local homeowners. Testing is the prudent default for every Front Range home, new or old, finished basement or slab. New construction is not exempt, since the gas comes from the ground beneath the foundation regardless of build quality. Buyers in the region increasingly include radon testing as a standard part of due diligence, and sellers who have already mitigated can present a passing post-test as a selling point. Given how common elevated readings are locally, treating radon as an expected line item rather than an unlikely surprise serves Colorado households well.
Common misconceptions about radon in homes
Several myths lead homeowners to skip testing. One is that a new home is safe, when in fact radon comes from the ground and even new construction can read high; build quality affects entry but not the source. Another is that a neighbor’s low reading means your home is fine, but radon varies dramatically house to house depending on soil, foundation, and construction, so an adjacent home’s result tells you little about your own.
A third misconception is that radon is only a basement problem irrelevant to homes without basements. Slab-on-grade homes and homes over crawl spaces can also accumulate radon, because the gas enters wherever the structure contacts soil. A fourth is that you would feel symptoms if radon were present; there are no acute symptoms, which is precisely why testing is the only reliable detection method. Clearing up these myths is often what moves a household from inaction to testing.
When and how often to test
The EPA recommends testing every home and retesting under several circumstances. A home should be tested if it has never been measured, before buying or selling, after finishing a basement or adding living space below grade, and after major structural or HVAC changes that could alter how soil gas enters or moves. Even a previously mitigated home benefits from periodic retesting to confirm the system is still working.
Short-term tests, run under closed-house conditions for two to seven days, give a fast screen, while long-term tests over 90 days or more better capture the annual average that drives long-term risk. An elevated short-term result is commonly confirmed with a follow-up before committing to mitigation. For Front Range homes, where elevated readings are common, building a simple testing habit, an initial test and periodic rechecks, is the most reliable protection a household can adopt, and a certified professional can guide interpretation when results are borderline or high.
Radon in water versus radon in air
Most attention focuses on soil gas because it accounts for the large majority of indoor radon, but radon dissolved in water from a private well can be a secondary source. When that water is used for showering, dishwashing, or laundry, agitation releases some of the dissolved radon into the indoor air, adding to the airborne level. Homes on municipal water supplied from surface sources rarely face this, because radon largely dissipates before delivery.
The practical implication is that homeowners on private wells in radon-prone areas may want to test the water as well as the air, particularly if air testing shows elevated levels that mitigation of the soil-gas pathway does not fully explain. Treatment for waterborne radon is a separate process from air mitigation, typically involving aeration or activated-carbon systems at the point of entry. For most Front Range homes on community water, soil gas remains the dominant concern, and sub-slab depressurization is the appropriate response.
Putting radon in perspective for households
Radon is a serious but entirely manageable hazard, which is the most useful way for a household to frame it. Unlike many home risks, it is cheap to detect and reliable to fix: a test kit costs little, and a mitigation system, where needed, brings levels down dependably. The danger lies almost entirely in not knowing, because the gas gives no sensory warning and the health effects accumulate silently over years.
For Colorado families, where elevated readings are routine, the sensible posture is to treat radon as a known, addressable feature of the local environment rather than a rare threat. Test the home, confirm an elevated result, mitigate if the level reaches the action threshold, and retest periodically. That short sequence converts an invisible, intimidating risk into a routine maintenance item. When a result is high or a household is unsure how to interpret it, a certified radon professional provides the home-specific guidance that turns a number into a clear plan of action.
References
- Health Risk of Radon — U.S. EPA
- Colorado Radon Program — Colorado Department of Public Health and Environment
- Radon and Lung Cancer Risk — American Lung Association
If your Front Range home has tested high for radon and you want a vetted professional to plan mitigation, reach out through our contact page.