Radon Pathways

Radon can enter your home via a number of entry points or pathways:

A – Cracks in concrete slabs
B – Spaces behind brick veneer walls that rest on uncapped hollow-block foundations
C – Pores and cracks in concrete blocks
D – Floor-wall joints
E – Exposed soil, as in a sump or crawl space
F – Weeping (drain) tile, if drained to an open sump
G – Mortar joints
H – Loose fitting pipe penetrations
I – Open tops of block walls
J – Building materials: brick, concrete, rock
K – Well water

In general, whenever air enters a home from the underlying soil, some radon will likely come with it

Foundations

Any home can have a radon problem, no matter what type of foundation it has.

If you have a basement: A basement provides a large surface area in contact with soil material. Radon can enter through cracks in the concrete, or through floor-to-wall joints or control joints. Since many Illinois homes use their basements as living space, exposure to radon can be further increased.

But radon can enter a home regardless of whether or not there is a basement.

Slab-On-Grade: Slabs built on grade can have many openings that allow radon to enter, just as in a basement.

Crawl Space: Homes with crawl spaces can also have elevated radon levels. The vacuum effect can draw radon gas from a crawl space into the home.

Manufactured Homes: Unless these buildings are placed on supports without skirting around them, interior air pressure vacuums can cause radon to enter manufactured homes, as well.

Radon and Your Home’s Air Pressure

Illinois homes commonly operate under a negative air pressure, especially during the heating season. What this means is, the air pressure inside your home is typically lower that the surrounding air and soil. This creates a vacuum that pulls soil gases, such as radon, into the home via pathways. Even if the ground around the house is frozen or soaked by rain, the gravel and disturbed ground underneath the house remains warm and permeable, attracting radon gas from the surrounding soil.

Other factors also contribute to air pressure changes in a home, including:

  • Stack Effect: As warm air rises to the upper portions of a home, it is displaced by cooler, denser outside air. Some of that displaced air comes from the soil.
  • Down Wind Draft Effect: Strong winds can create a vacuum as they flow over the top and around the home.
  • Vacuum Effect: Combustion appliances like furnaces, hot water heaters and fireplaces, as well as exhuast fans and vents, can remove a considerable amount of air from a home. When air is exhausted, outside air enters the home to replace it. Some of this replacement air comes from the underlying soil.

 What Happens After Radon Gets Into the Home?

Radon levels are often highest at the entry point – typically in the lower part of a building. As radon gas moves upward, diffusion, natural air movements and mechanical equipment (such as a forced-air ventilation system) distribute the radon through the home. Radon gas becomes more diluted in the upper levels of the home because there is more fresh air for it to mix with.

Greater dilution and less house vacuum effect occur when the house is more open to the outdoors, as during the non-heating season. This generally results in lower indoor radon levels in the summer compared to the winter.