The materials used to construct a foundation can often be used as an effective barrier to the entry of radon-laden soil gas. Below-grade walls may be constructed of poured concrete, masonry, or other materials such as pressure treated wood or stone. Poured concrete and masonry block are the most common materials in new construction.
In residential buildings, the foundation walls and floor made of poured concrete are generally constructed to a compressive strength of 2,500 to 3,000 psi. A poured concrete wall is a good barrier to radon transport. The major points of radon entry are the cracks, joints and other penetrations. It is these openings in the walls that allow soil gas to enter the building.
Residential foundation walls built of concrete masonry (concrete block) may have open cores, filled cores or cores closed at the top course. Masonry walls are frequently coated with an exterior layer of cementitious material, referred to as "parging," for water control. This coating is usually covered at the bottom of the wall to make a good exterior seal at the joint between the footing and the block wall, thus preventing the entry of radon into the house. Research indicates that homes with concrete-block foundation walls typically have twice the radon level as homes with poured-concrete foundations.
Waterproofing and damp-proofing are effective methods of sealing the joints and thus preventing the entry of radon. The most common damp-proofing treatment for residential foundation walls is an exterior parge coat of bituminous asphalt. The parge coat is used for concrete masonry walls but is not necessary for poured concrete.
The following are some of the damp-proofing/waterproofing systems suitable for radon barriers.
|Coal tar polyurethane|
|Membrane waterproofing systems|
Types of membranes available:
|High-strength bubble-pack with aluminum foil.|
|Aluminum foil over a core of glass scrim webbing.|