In a small number of homes, the building materials (e.g. stone, gravel, stone etc.) can give off radon, although building materials rarely cause radon problems by themselves

How Radon gets into your home: 

1. Cracks in concrete slabs.

2. Spaces behind brick veneer walls that rest on uncapped hollow-block foundation.

3. Pores & cracks in concrete blocks.

4. Floor-wall joints.

5. Exposed soil, as in a sump.

6. Weeping (drain) tile, if drained to open sump.

7. Mortar joints.

8. Loose fitting pipe penetrations.

9. Open tops of block walls.

10. Building materials (e.g. stone, gravel, stone etc.).

11. Water (from some wells).