Radon Mitigation with Sub-Slab Hazards - American Radon Mitigation

Radon Mitigation with Sub-Slab Hazards

Radon mitigation requires drilling into the slab, so what do we do when we encounter sub-slab hazards? Read on to see how we mitigated this home in New Brighton, Minnesota, with copper boiler lines beneath the slab. 


Before we get started, let’s review some radon mitigation basics. Radon is a radioactive gas released from the decay of uranium in rocks and soil. It can rise from the ground and collect in your home. Radon is the second leading cause of lung cancer in the United States behind smoking. Testing is the only way to tell if your home has elevated radon levels. Learn more about testing here.

Installing a radon mitigation system is the best way to lower radon levels. A mitigation system works by creating a vacuum under the home. The system sucks up the radon-laden air beneath the home and exhausts it out through the roof. Therefore, to create the most effective system possible, we need to create a vacuum under every area of the home. To ensure we are creating a proper vacuum, we perform pressure field extension testing. We drill small, half-inch holes in various places throughout the customer’s basement and seal in tubes that run back to micromanometers, devices that tell us how much negative pressure or suction we are creating in each test hole.



Now that we’ve covered some basics let’s look at how we mitigated this 1966 home with an initial radon level of 6.6 pCi/L.

The house had baseboard heat, so there were copper lines that ran beneath the slab back to the boiler.

Baseboard Heat

To locate the boiler lines below the slab, we reached out to Radar Guys with Definitive GPR.  They used a transmitter to locate the lines and a sewer camera to find the plumbing.


We put our first suction point about three inches from the copper boiler lines.

First Suction Point

The pipe ran up from that first suction point through the chase. So we had to maintain an inch of clearance from the double-wall B vent. We also had a single wall B vent a little lower down. We’re supposed to stay six inches away from the double-wall B vent, so we used a piece of thermal shielding metal to allow us to put the pipe where we wanted it.

We also wanted to make sure that the boiler remained accessible for future maintenance, so we used rubber couplers to make a section of the pipe removable. Then, when someone needs to access the boiler, they can simply loosen the rubber couplers, undo the clamps holding the pipe in place, and pull out that section. We wrote instructions directly on the pipe.

Access to the boiler

The pipe ran up through the chase, so it wasn’t visible in the closet above. We placed the radon fan in the attic and exhausted the pipe through the roof at the back of the house so that it would not be seen from the street.


Unfortunately, our first suction point did not create adequate suction in each of our test holes. Our next step was to get next to plumbing to take advantage of any settling. We had a couple of options. First, we could come across the ceiling in the next room, drop it down, and have the customer soffit the pipe in later. Our other option was to stitch from our first suction point, under the wall, into the next room. The customer opted for stitching. They were planning to remodel their house so we could pull the carpet up without worrying about it. We cored two five-inch holes through the slab and dug a tunnel to our main suction point on the other side of the wall to the left and a tunnel to the settling by the plumbing to the right. That helped us reach one of our five test holes.



For our second suction point, we teed off our main riser. 

Second Suction Point

We ran the pipe through floor joists, through a closet above the drywall, dropped below the floor joist in that closet, and ran across the wall to another closet on the opposite side of the room.
Radon pipe ran through floor joists

  The customer will soffit the pipe in later when they remodel.

Radon Pipe

Inside this third closet, we dropped down to our second suction point. You can see the tape marking the boiler lines below. Radar Guys also helped us locate the footing. We stitched under the footing over to the living room.

Marked boiler lines


In the living room, we pulled up the carpet and cored five stitching holes over to the walkout, where we typically find some settling. We were also able to get close to plumbing.

Stitching by walkout


In the laundry room, we had to cut out the back of the sink cabinet to seal a massive air leak. Initially, the sheetrock along the back of the cabinet ran all the way down, and they poured the slab up to it, leaving a half-inch gap. That gap pulled in a lot of conditioned air from the house and didn’t allow us to reach very far, especially in the walkout corner. Upon the customer’s approval, we cut out the back of the cabinet and the sheetrock so we could foam the gap.

Sealing air leak


Finally, we put our radon fan in the garage attic. We used a FanTech Rn4EC dialed into 7, which gave us the pressure field extension that we wanted. We ended up at 83 watts and 60 CFM. Figuring 25 of that was coming from the house as conditioned air loss, we estimated our operating costs would be about $184 a year. 


When we started the fan, levels were at about 3.8 pCi/L. After running the fan for a while, we saw levels drop to 0.35 pCi/L.

Radon Mitigation Results

At American Radon Mitigation, our goal is to create quality systems that lower radon levels as much as possible. Contact us to learn more about testing options or get a free quote for a mitigation system.