Radon Mitigation in New Construction: A Clear Guide
The cheapest, easiest time to make a home radon-resistant is before the concrete is poured. Building radon control into new construction costs a fraction of retrofitting it later, and many builders in high-radon regions now include it as standard. The result is either a passive system that vents soil gas on its own or a “rough-in” that can be activated with a fan in an afternoon if testing shows the home needs it. This guide explains how radon mitigation works in new construction and why it pays to plan for it. It summarizes EPA and Colorado Department of Public Health and Environment guidance current as of 2026 and is educational only — confirm requirements with your builder and a certified professional.
How does radon mitigation work in new construction?
In new construction, mitigation is built into the foundation as the home goes up. Crews lay a layer of clean gravel beneath the slab to let soil gas move freely, place a vapor barrier over it, run a vent pipe from the gravel up through the building and out the roof, and seal the slab penetrations. This is called a passive radon-resistant system. In many homes the natural stack effect — warm air rising and drawing soil gas up the pipe — vents enough radon without a fan.
If a post-construction test shows levels still at or above 4.0 pCi/L, the system is “activated” by adding an in-line fan to the existing pipe, converting it to active soil depressurization. Because the pipe and gravel are already in place, that upgrade is quick and inexpensive compared with a full retrofit. These are the same components found in retrofit systems, described in our guide to radon piping and system routing.
This two-stage design is what makes radon-resistant new construction so sensible. The expensive, disruptive parts — the gravel layer, the vapor barrier, the pipe run through finished walls, and the electrical rough-in — are installed while the home is open and easy to work in. The fan, which is the cheap part, is added only if testing proves it is needed. A builder following the EPA’s radon-resistant new construction guidance gives the buyer a home that is either already protected or can be protected in an afternoon.
Why build radon resistance into a new home
The Front Range sits in EPA Radon Zone 1, the highest-risk tier, where the predicted indoor average exceeds the 4.0 pCi/L action level. The EPA identifies radon as the second-leading cause of lung cancer and the leading cause among people who never smoked. New homes are not immune — tight, energy-efficient construction can actually trap radon more effectively than a drafty older house.
Cost is the deciding argument. Installing radon-resistant features during construction adds a modest amount to the build, while retrofitting an existing slab later costs considerably more because crews must core through finished concrete and route pipe through completed living space. Planning ahead is simply cheaper, which our breakdown of radon mitigation cost in Colorado illustrates.
Building codes increasingly reflect this logic. Many jurisdictions in high-radon areas have adopted radon-resistant construction requirements based on the model building codes, mandating the gas-permeable layer, barrier, and vent pipe in new homes. Front Range buyers should ask whether their builder follows these provisions and whether the local code requires them. Even where the rough-in is mandated, the fan and the post-construction test are often the buyer’s responsibility to verify, so it pays to know exactly what the contract includes.
Components of a new-construction radon system
Five elements make a home radon-resistant from the ground up.
Gas-permeable layer and barrier
A four-inch layer of clean gravel under the slab lets soil gas flow toward the vent pipe. A polyethylene vapor barrier laid over the gravel and across the soil reduces how much gas reaches the slab in the first place.
Sealed slab and vent pipe
All openings in the slab — control joints, the sump cover, pipe penetrations — are sealed so gas cannot bypass the system. A vertical PVC vent pipe runs from the gravel layer up through the home and exits above the roofline.
Fan-ready rough-in
An accessible section of pipe, usually in an attic or garage, plus a nearby electrical junction box, lets a fan be added later without opening walls. This rough-in is what makes activation a short job rather than a major project.
Labeling and the manometer
A complete radon-resistant build also includes clear labeling on the vent pipe identifying it as a radon system, so future owners and contractors do not mistake it for plumbing or disconnect it. When the fan is activated, a manometer is added to show suction at a glance. These small touches matter because a system that outlives the original owner’s memory still needs to be recognizable and maintainable years later.
Why builders favor the passive design
Builders include the passive rough-in partly because code increasingly requires it and partly because it is inexpensive to add during framing. From the builder’s standpoint, installing gravel, a barrier, and a length of PVC pipe is trivial compared with the cost and disruption of returning to retrofit a finished home. The design also limits the builder’s exposure, since the buyer can confirm the result with a test and activate the fan if needed, rather than the builder guaranteeing a specific radon level in soil conditions no one fully controls.
Passive versus active in a new home
A passive system relies on natural airflow and works well in many homes, but it does not guarantee levels below the action level. That is why testing after move-in is essential. If the passive system holds radon under 4.0 pCi/L, nothing more is needed. If not, the fan-ready rough-in is activated.
Some builders and buyers in high-radon areas choose to install the fan from the start rather than wait, since the marginal cost is low and active systems are more dependable. Either way, the decision should follow a test, not an assumption — radon varies house to house even on the same street, as our guide to radon readings in homes explains.
Cost comparison: build-in versus retrofit
The financial case for building radon resistance in is straightforward once you compare the two paths. During construction, the gravel layer, vapor barrier, sealed slab, and vent pipe are installed while the home is open and crews are already on site, adding only a modest sum to the overall build. The fan, if needed, is a small additional cost added later.
Retrofitting an existing home tells a different story. Crews must core through finished concrete, route pipe through completed living space or up an exterior wall, and work around finishes the homeowner wants to protect. A full retrofit is a mid-range home expense, considerably more than the build-in approach, and it can involve cosmetic compromises like a visible pipe running through a closet. The lesson for anyone building or buying new is to make sure the rough-in is included from the start, so the home never needs the more expensive retrofit path.
Testing the finished home
A radon-resistant build is not proof of low radon — it must be confirmed by a test. Test the home after occupancy under closed-house conditions, ideally during the heating season when levels run highest. If the result is at or above 4.0 pCi/L, activate the system and re-test to verify the fan brought levels down.
Timing the first test deserves thought. A brand-new home should be tested once it is occupied and operating normally, with the HVAC running and the house lived in, because an empty or unconditioned home does not reflect how radon will behave day to day. If possible, schedule that first test during fall or winter, when sealed, heated homes show their highest readings. A summer test on a new home can read low and give false comfort, so a follow-up during the first heating season is wise even if the initial result looked fine.
Buyers of new homes should ask the builder whether radon-resistant features were installed, request documentation, and arrange their own test rather than relying on the builder’s word. Re-test every two years thereafter, as with any home.
What can go wrong in a new-construction system
A radon-resistant rough-in only protects the home if it was built correctly, and a few defects show up regularly. A vent pipe that is not properly sealed where it passes through the slab can leak, and a barrier that was torn during the pour loses much of its effect. The most common shortfall is a system that was roughed in but never tested, leaving the buyer to assume protection that may not exist.
Another issue is a passive system that genuinely is not enough. Passive venting depends on the stack effect, which is weak in some homes and seasons, so a home can pass on paper yet test high in practice. The remedy is the same in every case: test the finished home and activate the fan if the number warrants it. A buyer who treats the rough-in as a promise rather than a guarantee, and verifies with a test, avoids the trap of unprotected new construction.
New-construction radon on the Front Range
For Colorado buyers, the new-construction conversation matters because the entire region sits in EPA Radon Zone 1. A brand-new home in Douglas, El Paso, or Adams County is just as likely to draw radon from the soil as an older neighbor, and its tight, energy-efficient envelope can trap that gas effectively. The radon-resistant rough-in is not a luxury here; it is the baseline a prudent buyer expects.
Fold the radon test into your new-home walkthrough or first weeks of occupancy, ideally during the heating season. If the rough-in is present and the test comes back low, you have confirmation rather than assumption. If it comes back high, activating the fan is a quick, affordable step that turns the builder’s foresight into real protection.
Questions to ask your builder
Buyers of new homes have leverage during construction that disappears once the home is finished, so it pays to ask the right questions early. Find out whether the home includes a passive radon-resistant system and whether local code requires one. Ask to see the specifics: the gas-permeable layer, the vapor barrier, the location of the vent pipe, and where the fan-ready rough-in is accessible. Confirm whether activating the fan, if needed, is included in the price or an extra cost.
Get the answers in writing as part of the contract or the home’s documentation. A builder who readily explains the radon features and provides documentation is showing the kind of transparency you want. Vague answers, or a claim that the home “doesn’t need” radon resistance because it is new, are warning signs in a Zone 1 region. New homes are not exempt from radon, and a buyer who insists on clarity protects both their family and their investment.
When to call a professional
Call a certified radon professional to test a newly built home after move-in, to activate a passive system that tests high, or to evaluate whether a builder’s rough-in was installed correctly. Discuss radon-resistant construction with your builder before the slab is poured if it is not already standard in your contract. In Colorado, look for technicians certified through AARST-NRPP or NRSB, and insist on a confirming test after any fan activation.
References
- Building Radon Out: A Guide to Radon-Resistant Construction — U.S. Environmental Protection Agency
- Radon Information for Colorado Residents — Colorado Department of Public Health and Environment
- A Consumer’s Guide to Radon Reduction — U.S. Environmental Protection Agency
Building or buying new on the Front Range? Confirm radon resistance was done right and have the finished home tested. Reach out through our contact page and we’ll connect you with a certified local radon professional.