How Does Radon Enter A Home: Entry Points & Prevention

Radon is a dangerous, cancer-causing gas that can be found in many homes in the USA. But have you ever wondered how this gas enters your home?

Radon gas enters a home mainly through the cracks and holes in its basement floor and the walls. It can also enter through the exposed soil in the basement and the crawlspace. Another point of entry is through the water if it is coming from a well.

Radon gas is formed through the decay of uranium deposits in the soil under your house. This gas slowly moves up through the soil and finally into the atmosphere. It enters the house from the soil beneath it. In addition, houses have a slight negative pressure in them when compared to the outside. This negative pressure sucks the radon in, like a vacuum cleaner. This causes the gas to force its way into the house through anywhere that offers it a path.

A house

Entry points for radon gas

Given below are the main paths through which radon gas enters a home.

Exposed soil

Not all basements are finished. Also, many houses have crawlspaces instead of basements. For such houses, the floor is just soil. As you know, radon gas is formed from the soil deep below your, so a soil floor doesn’t offer any resistance to its passage. This means that exposed soil is the main entry point of radon into a house.

Drain tiles

The next big entry point of radon is the drain tiles in your basement. A finished basement floor act as a barrier that prevents radon from entering a house. However, the drain tiles of the basement offer a path of least resistance for the gas. So the whole radon gas blocked by the finished basement will concentrate at the draintiles and seep into the house through them.

Sump pumps

Sump pits are made to collect the water that collects under your basement because of rainwater and groundwater. Just like how water under the floor ends up in the sump pit, the radon gas also gets collected there. An unsealed sump pit is a source of highly concentrated radon gas.

Floor-wall joints

The tiny space between the wall and the floor is a common entry point for radon gas. If this space remains unsealed, it offers no resistance to the gas from entering the house. So such joints must be sealed properly.

Pipe penetrations

A lot of pipes go through basements and crawlspaces. The holes made for the pipes that come from the outside allow radon to enter the house. More than often, the pipes are fitted into these holes loosely. So the space between the pipes and the wall offers an easy passage for the radon gas. Therefore, these spaces need to be sealed properly.

Cracks in concrete slabs and walls

Since the basement is constructed below the ground level, radon can seep into it through the walls and the floor. Even if the walls and floors are well made, there always will be some tiny entry points for radon.


Radon gas is mildly soluble in water. Therefore, groundwater always contains some radon. If your water supply system uses groundwater, some of the gas can dissipate into the air. The radon content in water doesn’t significantly increase the radon concentration in a house. A 10,000 pCi/L of radon content in water can only raise the radon level in the house by 1 pCi/L. For this reason, EPA hasn’t set a specific level of radon in the water supply. However, a general guideline is to mitigate radon from water if its levels exceed 4,000 pCi/L.

So the before mentioned are the main points of entry where radon gas can seep into a house. Here you have learned how radon gas enters a house and where to look for it.

Ways to prevent radon from entering the house

It is impossible to prevent radon from entering a home completely. What one can do is reduce the amount of radon entering. This can be achieved by;

Seal cracks and other entry points

Sealing the cracks in the walls and the basement floor can significantly reduce radon entry. The joining of the walls with the floor should be caulked to prevent radon from entering through those points. If you have a sump pump, it should be sealed with a sump cover.

Use vapor barrier

Covering the dirt floor of the basement and crawl space can significantly reduce radon levels in a home. In fact, using a vapor barrier is the only way to prevent radon entry if you have an unfinished floor. Make sure that the barrier is properly sealed with the walls, and that it has no holes.

Avoid the use of exhaust fans

The rate of radon gas entering a home will be high if the house has negative pressure. The use of exhaust fans in the basement increases the negative pressure pulling more radon gas inside. Therefore, to reduce radon gas entry, basement areas shouldn’t use exhaust fans. It is recommended to use natural ventilation or heat recovery ventilation.

Install a mitigation system

A radon mitigation system removes radon gas from the soil before it enters a house. It creates negative pressure under the basement to collect the gas and vent it outside the house. Charcoal-based filtration systems are available to remove radon from water. However, these systems are costly and are recommended to be used only if the above methods do not work.

Charles John

A novice DIYer who learns about home ventilation. I am a mechanical engineer and have a basic knowledge of HVAC systems but I learn continuously to make myself the best blogger in that space.

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