Controlling Radon Gas

In Existing Homes:

After testing for radon and if the level exceeds 4.0 picocuries, the next step is to begin mitigation. You should look for a ‘certified mitigation contractor’. They will have completed the EPA required training and testing. In a nutshell mitigation for an existing home includes the following:

  • Cover all exposed earth with a 6 mil poly and seal all edges.
  • Caulk all cracks and openings in the floor slab.
  • Put a 3” pipe in the earth, thru the floor slab, or in a sump.
  • Install the pipe inside or outside the house.
  • Extend the pipe a 12” above the surface of the roof.
  • Pipe must terminate minimum of 10’ from a window
  •  Pipe must terminate 10’ from another home.
  • Re-test and verify a level of 4.0 picocuries or less.

In New MN Homes:

There is no preliminary testing. The state requires either a passive or active system that consists of the following construction requirements:

Below the floor slab a minimum of 4” of gas –permeable aggregate or sand.

  • Cover the sand or aggregate with a minimum 6 mil poly overlapped a minimum of 12”.
  • All penetrations thru or joints in the slab must be caulked.
  • Hollow core blocks must have at finished grade a solid course of blocks.
  • Exterior walls of foundation must be dampproofed below grade.
  • Ducts below the slab must be continuous or sealed.
  • A plumbing tee inserted below the floor slab and poly.
  • A minimum 3” pipe extended thru the building and marked as radon pipe.
  • Pipe must terminate 12” above the roof and a minimum of 10’ from a window or another house.
  • A fan (active) is optional.  No fan (passive) or radon testing is required.

Radon gas is real…this hazard should be taken seriously.

Doug Hastings
MN Home Inspector, Minneapolis & St. Paul
ASHI Certified Inspector, ACI
Kaplan University, Home Inspection Lead Instructor

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