How Does Radon Get Into Your Home? (The Science Made Simple)

Most homeowners who learn about radon for the first time ask the same question: if it comes from the ground, how does it end up inside my house? The answer has everything to do with the way homes are built and the way air moves through them. Understanding how radon enters is also the first step toward understanding how it can be stopped.

Your Home Acts Like a Vacuum

The key to understanding radon entry is air pressure. The air inside your home is almost always at a slightly lower pressure than the air in the soil beneath and around your foundation. This pressure difference — even when it is very small — creates a constant gentle suction effect. Your home is essentially drawing air upward from the ground below it.

That air carries radon with it.

This is not a flaw in how your home was built. It is simply physics. Warm air rises and escapes through the upper levels of a home, creating negative pressure at the lower levels that draws outside air — and soil air — inward to replace it. This effect is strongest in basements and on the lowest floors, which is why radon concentrations are typically highest closest to the ground.

The Entry Points Radon Uses

Radon is a gas, which means it can move through openings that would stop water or insects. Even a structurally sound foundation has pathways radon can exploit. The most common entry points include:

Foundation cracks and gaps. Concrete is not perfectly solid over time. As homes settle and go through seasonal freeze-thaw cycles — something Michigan homes experience intensely — small cracks develop in basement floors and walls. These cracks do not need to be large or visible to allow radon entry. Even hairline cracks are sufficient.

Construction joints. Where the floor meets the wall in a poured concrete basement, there is a joint where two separate pours of concrete meet. This joint is rarely perfectly sealed and is one of the most common radon entry points in basement construction.

Pipe and utility penetrations. Every home has pipes, wires, and conduits passing through the foundation — water lines, drain pipes, electrical conduits, gas lines. The gaps around these penetrations, even when they appear sealed, are frequent radon pathways.

Sump pits and floor drains. Sump pits are particularly significant entry points because they are open cavities in the floor connected directly to the soil and groundwater below. Without a sealed cover, a sump pit is essentially an open channel between the ground and the air in your basement. Floor drains present a similar issue.

Block foundation walls. Homes built with concrete block rather than poured concrete have hollow cores inside the blocks. Radon can travel up through those hollow cores and enter the living space through openings at the top of the wall.

Crawlspaces. Homes built over crawlspaces rather than full basements are not immune. Exposed soil in a crawlspace is in direct contact with the home's air, and radon rising from that soil moves directly into the space beneath the living areas above.

Once Inside, Where Does It Go?

Once radon enters through any of these pathways, it mixes with the air in your home. In a well-ventilated space, it would dilute relatively quickly. But most homes — and particularly Michigan homes during the long heating season — are not well ventilated. Radon accumulates in the lower levels of the home first and then gradually migrates upward through the house.

This is why finished basements used as living spaces carry particular exposure risk, and why even upper floors in a home with high basement radon levels are not entirely insulated from the problem. Radon does not stay neatly contained where it enters — it becomes part of the air throughout the home.

Why Sealing Alone Is Not Enough

A natural first instinct when learning about radon entry points is to think that sealing cracks and gaps would solve the problem. It is a reasonable thought, but sealing alone is rarely an effective long-term solution.

The challenge is that the pressure differential driving radon into your home does not go away when you seal one crack — the gas simply finds or creates another pathway. Foundations develop new cracks over time. Sealants degrade. The physics driving the air movement are constant and ongoing. Sealing can be a useful supplementary step, but it is not a substitute for a properly installed mitigation system that addresses the underlying pressure dynamic directly.

Understanding how radon enters is ultimately what makes modern mitigation so effective. Rather than trying to block every possible entry point — an endless task — a mitigation system changes the pressure relationship between your home and the soil beneath it, removing radon before it ever gets a chance to enter. That approach works with the physics rather than against it.

The Takeaway

Your home's construction is not the problem — it is simply the environment radon navigates. Every home built on soil has potential entry points, and in a high-risk region like West Michigan, the geology beneath those homes is actively producing radon gas. Knowing how it gets in is the foundation for knowing how to address it.

If you have questions about radon entry, testing, or what a mitigation system involves, All Michigan Mitigation is here to help. We serve homeowners throughout West Michigan and specialize exclusively in radon testing and mitigation.

Visit us at allmichiganmitigation.com to get started.

All Michigan Mitigation is a West Michigan radon testing and mitigation company dedicated exclusively to helping homeowners understand and eliminate radon risk in their homes.