How Does Radon Enter Your Home?

Radon is a radioactive gas that can cause lung cancer over time. It comes from the ground and can enter your home through cracks in floors, walls or foundations.

Households are most affected by radon because indoor air pressure is lower than outdoor pressure, allowing radon to be drawn in. Building materials like concrete, wallboard and granite countertops can give off radon, too, as can water from wells.


Radon enters homes from the soil through cracks in foundations and walls. It also can seep into the air from well water and building materials. The radon enters your home as a gas and accumulates inside, increasing the risk of lung cancer. It is the second leading cause of lung cancer in smokers and increases the risk for non-smokers as well.

Radon is a radioactive element that forms as uranium, thorium and radium break down in water, rocks and soil. The radon is then released in the air, and it can get into your house through foundation cracks, basement windows and doors, or even through gaps around utility openings. It can also enter through the ground into your home from water if it contains uranium, but this is much less common.

A high concentration of radon can develop in basements, crawl spaces, and living rooms where it gets drawn upward by pressure differences within the house (from warm air rising and furnace/air conditioner exhaust). It can also enter through the ground into the lower level of a slab-on-grade home. It can also be driven into a basement by water appliances (washing machines, dishwashers, clothes dryers, and hot water heaters), allowing it to move through cracks in the floor and walls. It can also be carried into the house by a forced-air system that brings in outside air (furnaces, heat pumps and air conditioning). Some homes built on slabs or crawl spaces have higher radon levels than those with basements.

Crawl Spaces

A crawl space is a place often out of sight and out of mind, but this area is still exposed to the soil, making it an important entry point for radon. Crawl spaces with dirt floors are especially prone to elevated radon levels as they act like open windows and provide a pathway for radon gas to enter the home above.

Radon forms when uranium, thorium, and radium break down in water, rocks, soil, and building materials, releasing radioactive gas that can travel through the ground to the living areas above. This can be a problem for homes built on slabs, but it’s also an issue in houses with basements. Radon can also travel from crawl spaces into living areas through different pathways, including cracks in the foundation, gaps in floor and walls, old furnace vents, and ductwork.

Radon that enters your crawl space can find its way into your home’s upper floors through the “Stack Effect.” This happens when air pressure in your house is lower than in the crawl space, causing the gas to get pulled up into the home. Once inside your living space, radon can build up to dangerous levels and cause health problems. To prevent this, a radon specialist can recommend a crawl space membrane and sub-membrane depressurization system. These systems can be vented mechanically or passively, depending on your needs.


Opening windows to ventilate a home may reduce radon levels temporarily, but it will not make a lasting difference. This is because a home will exchange its air about every 6-8 hours, through natural convection and through circulating the air with the furnace or AC system. This constant air movement actually can increase radon levels during a short-term test, and opening windows in the upper part of the home will make this effect worse.

The best way to reduce radon levels is to hire an experienced professional to conduct a radon test in your home. A professional will be able to determine how high your radon levels are, and recommend the appropriate treatment options.


Radon is a naturally occurring radioactive gas. It comes from the breakdown of uranium in soil, rock and water. It moves through these materials and into living spaces, where it can become trapped and concentrate to dangerous levels. Radon can also infiltrate drinking water.

The main way radon enters homes is by riding on soil gases that penetrate concrete foundations or a part of the structure in direct contact with the ground, such as a crawl space. It can also enter through loose-fitting pipe penetrations, floor-wall joints and cracks in walls and floors. Radon can even ride on air coming from heating, ventilation and cooling systems (HVAC) or through open windows and doors.

Most radon problems develop in basements, but any home can have a radon problem, including slab-on-grade or crawl space foundations, and even newer or well-sealed homes. The type of foundation a home has and other factors, such as the size of the house, its ventilation system, and the temperature differences between indoor and outdoor air, affect how much radon is pulled into the residence.

The EPA warns that while some parts of the country have higher radon levels than others, no home is safe from the risk. This is because radon can vary widely between adjacent homes. It can also change over time. This is why it’s important to test for radon regularly, and to have the EPA-recommended system installed if a test shows high levels.