--- title: Radon-Resistant New Construction (RRNC) Explained canonical: "https://radonmitigationyorkpa.net/radon-guide/radon-resistant-new-construction/" pubDate: "2026-10-01T00:00:00.000Z" updatedDate: "2026-10-03T00:18:00.000Z" author: Radon Mitigation York PA description: "The five parts of radon-resistant new construction, how a passive stack works, what it costs compared with a retrofit, and why you still need to test." --- # Radon-Resistant New Construction (RRNC) Explained [Radon-resistant new construction](/services/new-construction-radon/) (RRNC) is a set of building steps that help keep radon out of a new home. The core parts are a gas-permeable layer under the slab, a plastic vapor retarder, sealed foundation openings and a vent pipe from below the slab through the roof, with an attic electrical outlet so a fan can be added later. ## Why build radon resistance in from the start Radon is a colorless, odorless radioactive gas made as uranium breaks down in soil and rock. It moves up through the ground and into buildings through gaps in the foundation. EPA estimates radon causes about 21,000 lung cancer deaths a year in the U.S., and it is the leading cause of lung cancer among non-smokers. You cannot know a lot's radon level until the house is built and tested. RRNC sets the house up to handle radon either way. EPA notes the cost to the builder of including these features is typically less than the cost of mitigating the home after construction. ## The five basic parts of RRNC EPA's [radon-resistant construction basics](https://www.epa.gov/radon/radon-resistant-construction-basics-and-techniques) lists five features. Here is what each one does. ### 1. A gas-permeable layer EPA calls for about 4 inches of clean, coarse gravel under the slab. The gravel leaves open space so soil gas can move freely to a collection point. Where gravel is not practical, a soil gas collection mat (a flat, open plastic matrix wrapped in fabric) can serve the same purpose. ### 2. Plastic sheeting Heavy-duty polyethylene sheeting, which EPA lists as 6 mil, goes on top of the gravel and under the slab. It slows soil gas from moving up into the house and keeps the gravel clean during the pour. Seams should overlap and be taped. ### 3. Sealing and caulking All openings, cracks and crevices in the concrete floor get sealed, usually with polyurethane caulk. That includes the joint where the floor meets the wall, control joints, plumbing penetrations and any sump pit, which should get a sealed, gasketed lid. ### 4. A vent pipe A 3 or 4 inch Schedule 40 PVC pipe runs from the gravel layer up through the house and out the roof. EPA guidance places it in a vertical route through the conditioned part of the house, not up an outside wall, so warm air in the pipe helps draw soil gas up. The pipe is labeled on every floor so future owners and trades know what it is. ### 5. An electrical junction box An outlet or junction box goes in the attic near the vent pipe. If a test shows high radon after move-in, an in-line fan can be added to the pipe in the attic without new wiring runs. ## How a passive RRNC system works Without a fan, the system is called passive. Two things drive airflow in the pipe: - **The stack effect.** Warm air in the pipe rises, much like smoke up a chimney. That gently pulls soil gas from the gravel layer up and out. - **Wind.** Wind across the roof can add a small draw at the pipe outlet. Because these forces are small and change with the weather, a passive system's results vary. It may lower radon in some homes and do little in others. That is why every RRNC home still needs a test. ## Activating the system If a test after move-in shows 4.0 pCi/L or higher, the EPA action level, the next step is adding a fan. A radon fan installed in the attic section of the pipe turns the passive system into an active soil depressurization system. A U-tube manometer is added so you can see the fan is working, and a clearance test confirms the result. Some buyers choose to activate right away, without waiting for a test. Either approach works, as long as the home is tested afterward. ## RRNC standards and codes ### National standards Beyond EPA's guidance, ANSI/AARST publishes consensus standards for radon control in new construction. For one and two family homes and townhouses, the current standards cover reducing radon in new construction (CCAH) and rough-in of radon control components (RRNC). Larger multifamily, school and commercial buildings have their own new construction standard (CC-1000). EPA lists these on its [radon standards of practice](https://www.epa.gov/radon/radon-standards-practice) page. ### Pennsylvania Pennsylvania's Uniform Construction Code does not require RRNC statewide. The International Residential Code includes radon control methods in an appendix, and appendices only apply where a jurisdiction adopts them. The 2021 UCC update, in effect since January 1, 2026, did not adopt the radon appendix statewide. Some Pennsylvania municipalities have adopted it locally. Our guide to [Pennsylvania building code and radon](/radon-guide/pa-building-code-radon-requirements/) goes into more detail. ## Common RRNC mistakes A rough-in only helps if it is done right. These are the problems we see most: - **No gravel or mat.** Pouring the slab on tight soil leaves the pipe with almost nothing to draw from. - **Torn or unsealed plastic.** Rips and loose seams let soil gas bypass the barrier. - **Pipe on an exterior wall.** A cold pipe loses the stack effect and can freeze or condense. - **No attic access.** If the attic section of the pipe is buried in insulation or blocked by framing, adding a fan gets harder. - **Missing outlet.** Without an outlet, activation needs an electrician. - **Unlabeled pipe.** Future trades may cut into it or tie other plumbing into it. - **Open sump pit.** An unsealed pit gives soil gas an easy path around the whole system. ## RRNC in York County York County is in [EPA Radon Zone 1](https://www.epa.gov/radon/epa-map-radon-zones-and-supplemental-information), the highest radon potential category. That makes RRNC a sensible baseline for any new home here, whether it has a full basement or sits on a slab. York winters also help a passive stack, since the temperature difference that drives the stack effect is larger in cold months. Pennsylvania requires anyone who tests or mitigates radon for others, including activating a system, to be certified by PA DEP. ## Key takeaways - RRNC has five basic parts: gravel or a mat, plastic sheeting, sealing, a vent pipe and an attic outlet. - It costs less to include during construction than to retrofit later. - A passive stack may lower radon, but results vary, so test after move-in. - If the test is 4.0 pCi/L or higher, add a fan to activate the system. - Pennsylvania does not require RRNC statewide, but it makes sense in Zone 1 York County. ## Frequently Asked Questions ### Does RRNC guarantee low radon? No. It makes radon easier and cheaper to fix, and a passive system may lower levels. Only a test tells you the result. ### Can RRNC be added to a house that is already built? Not the under-slab parts. An existing house gets a retrofit system instead, with a new suction hole, pipe and fan. ### Is RRNC the same as a vapor barrier? No. A vapor barrier is one part of RRNC. The vent pipe, gravel layer and sealing are what make it a radon system. ## Plan RRNC for your build We rough in, test and activate RRNC systems for York builders and homeowners. Call [(717) 356-3035](tel:+17173563035) any time for a same-day callback and a free written quote.