Radon in Manufactured and Mobile Homes

1. Yes, manufactured and mobile homes get radon

Radon is a naturally occurring radioactive gas that comes from the breakdown of uranium in soil and rock. It does not care what kind of home sits on top of it. A manufactured home, a mobile home, a brick ranch, and a basement colonial all rest over soil, and that soil is the source. The idea that only basement homes have radon is one of the most common and most costly misconceptions, because it leads owners of crawl-set and skirted homes to skip testing entirely.

The thing that varies between home types is not whether radon is present in the soil, but how easily it travels from the soil into the air you breathe. A manufactured home raised on piers with open skirting, a home with tight skirting, a home over an enclosed crawl space, and a home set on a slab each create a different path between the ground and the living space. Understanding that path is the key to understanding the risk and to fixing it.

2. How radon enters a manufactured home

Radon enters a home the same way in every case: soil gas is drawn upward and indoors by small pressure differences. Warm air rising inside the home, exhaust fans, and the wind all lower the pressure inside relative to the soil, and that pressure difference pulls gas up out of the ground. In a manufactured home, the first place that gas collects is the space directly under the floor, whether that is an open crawl area between the ground and the home or the enclosed volume behind the skirting.

Once soil gas is in that under-floor space, the only thing between it and the living area is the floor of the home and whatever openings pass through it. The floor of a manufactured home is not a perfect seal. There are seams, the belly wrap can be torn or open, and every pipe and wire that comes up into the home is a potential entry point. That is why a home that feels tightly built can still draw radon up from below.

3. Why a skirted home behaves differently than a slab or basement

A slab home has concrete in direct contact with the soil, and radon enters through cracks, control joints, and the gap around the perimeter. A basement home has walls and a floor below grade, which gives soil gas a large surface to enter through. A skirted or crawl-set manufactured home is different again. The home is lifted off the ground, and the space underneath behaves like a small enclosed chamber that can either ventilate to the outside or trap soil gas, depending on how open the skirting is.

The practical takeaway is that you cannot predict a manufactured home result by looking at the foundation type. An open, breezy crawl can still have elevated radon if the soil under it is high in source material, and a well-sealed home can accumulate gas that has nowhere to vent. The construction influences the pathway, but the soil drives the supply, and only a test tells you what is actually happening in a given home.

4. Utility penetrations through the floor

The most reliable entry points in a manufactured home are the places where something passes through the floor. Plumbing supply and drain lines, the openings where a tub or shower drain drops down, electrical and wiring chases, and the ductwork that runs through the belly of the home all create gaps. Each one is a small channel that lets the gas collecting under the floor move up into the rooms where people spend their time.

Sealing these penetrations is a sensible first step and part of good practice, but sealing alone rarely solves an elevated radon problem on its own. Soil gas is persistent, and pressure differences will find the next available gap. That is why sealing is treated as a complement to an active mitigation system rather than a substitute for one. For the bigger picture on how radon finds its way indoors in any home, see our explainer on how radon enters your home.

5. How to test a manufactured or mobile home

Testing a manufactured home follows the same rule as testing any house: measure in the lowest lived-in area. For most single-level manufactured and mobile homes, the living space is the lowest occupied level, so the detector goes in a room you actually use, such as a main living area or a bedroom. Set it roughly two to six feet above the floor, away from exterior doors, drafts, direct sunlight, and sources of high humidity, and leave it undisturbed for the test period.

During a short-term test, keep windows and exterior doors closed as much as normal living allows, since wide-open ventilation can temporarily dilute the reading and hide a problem. If a short-term test comes back near or above the action level, a follow-up measurement confirms the result before any mitigation is designed. For why this matters even when a home seems fine, see why radon testing is essential.

6. Mitigation approaches for manufactured homes

When a manufactured home is set over a crawl space or skirted area, the standard fix is a form of sub-membrane depressurization. A durable plastic membrane is laid across the exposed soil under the home, sealed at the seams, at the perimeter, and around the piers and supports, so that it covers the ground the home sits over. This is the same principle used to control radon and moisture under conventional crawl-space homes, adapted to the way a manufactured home is set.

A vent pipe is then routed from beneath the membrane, and an in-line fan draws air out of the space under the membrane and exhausts it above the roofline. By keeping the area under the membrane at a slightly lower pressure than the home, the system pulls soil gas out and vents it safely outside before it can be drawn up through the floor. Sealing floor penetrations and any tears in the belly wrap is done alongside the system so the fan does the most work where it counts. The approach parallels the membrane method described in our guide to radon in crawl space homes.

7. Homes set on a slab

Not every manufactured home sits over an open crawl. Some are placed on a poured concrete slab or a runner of concrete, in which case the entry pathway and the fix both look more like a conventional home. Here the right approach is sub-slab depressurization: a suction point is created through the slab, a pipe and fan draw soil gas out from beneath the concrete, and the gas is vented above the roof. The fan keeps the area under the slab at lower pressure than the home so gas is pulled out rather than pushed in.

Because the foundation determines the right system, the first job on any manufactured home is to confirm how it is actually set before designing the fix. A skirted crawl, an enclosed crawl, and a slab each call for a different layout, and a mix of the two is not unusual on older homes that have been moved or re-set over the years.

8. A large housing segment in rural north Georgia

Manufactured and mobile homes are a major share of the housing stock across rural north Georgia. They are affordable, common, and often sited on land where the underlying geology is exactly the kind that produces radon. North Georgia sits on granite and uranium-bearing bedrock, and many counties in the region fall into higher-radon EPA zones. Put a large number of crawl-set homes on top of that, and the result is a lot of housing that should be tested and frequently is not.

For a manufactured home owner in north Georgia, the combination of elevated regional radon and a crawl-set or skirted design means testing is worth doing rather than assuming. The test is inexpensive and unobtrusive, and if the result is fine you have peace of mind, while if it is high there is a clear and proven path to fixing it.

9. Frequently asked questions