Mitigation, Aftermarket Drain Tile & Additions - American Radon Mitigation

Mitigation, Aftermarket Drain Tile & Additions

Aftermarket drain tile and additions can complicate the radon mitigation process. Let’s look at how we mitigated this 1967 Edina home with aftermarket drain tile, multiple additions, and a radon level of 8 pCi/L. 



The first addition was in the back corner of the house. The homeowner told us that there was drain tile in this addition. However, there wasn’t a sump basket, so we guessed that the drain tile routed to the sump pump on the other side of the wall on the right.

First addition

We pulled the carpet back and drilled a half-inch test hole through the slab. We drilled these test holes throughout the basement to use micromanometers to measure the amount of suction that the system generated throughout the house. Creating a vacuum under the entire house is the best way to lower radon levels effectively.

Test Holes

There was aftermarket drain tile in the finished portion of the basement. You can see that the slab was two different colors. The new, lighter concrete indicated where the drain tile was located. We added two test holes and sealed the cracks that we could find.

Drain Tile Added

Along that same wall, we placed another test hole. Again, the concrete there was all original. The drain tile covered about two-thirds of the basement, ending somewhere between the two corners of the carpet that we pulled up.

Drain tile covered about two thirds of the basement

There was a small bathroom separating the main area of the basement from an office by the front of the house. There was no drain tile in the office. We added a test hole there as well.

No drain tile in the office


Past the office was the unfinished portion of the basement and the second addition. The picture below shows the old corner of the house. The two doorways are where they went through the block wall to create this addition. They do have drain tile along an exterior wall in this addition.

Second Addition

This area of the house had waffle board, a plastic drain tile product that ran against the foundation wall and sat on top of the footing. They poured the slab up to the waffle board, which created an air gap between the block or the poured foundation and the concrete floor. Water that ran down the wall could get into that gap, into the drain tile system, and over to the sump basket. That gap behind the wall was a soil gas entry point, which allowed radon inside the home. The air leak would result in a massive energy penalty if we tried to depressurize the drain tile system. It would also likely create back-drafting issues where it would pull a lot of conditioned air into the radon system and exhaust it outside.

Waffle Board Used

We labeled the sump in the addition to make it easy for somebody to replace it. We put a test hole on the sump, where we had the weakest suction.

Test hole on the sump

Looking at the concrete, we saw that the aftermarket drain tile ran along the old wall of the house and stopped before the addition.

Aftermarket drain tile


There was another sump in the original part of the house where we used sump suction. We find sump suction gives us the most energy efficiency in houses with aftermarket drain tile.

Sump Suction

There was a 4-inch perforated pipe below the slab and no waffle board. It was just concrete poured up to the block wall.


When installing drain tile, they jackhammer the floor and drill a hole in each block core where they’ll insert a small section of hose, usually about a foot long and a half-inch in diameter, called a weep hose.  Any water inside the hollow block can drain from the block into that weep hose and into the drain tile system. When we depressurize the drain tile system, we also depressurize that weep hose and block wall. If the top of the block or any penetrations are not sealed, the system will pull conditioned air from the house. If that happens, it’s likely to backdraft a natural draft water heater. We sealed as much as we could. However, in the finished areas of the basement, we did not cut open drywall to seal.

Seal top of block wall



We used a damper to adjust the amount of air the system pulled from this suction point.

Damper to adjust air in the system


We still did not have adequate suction in the office at the front of the house. Therefore, we placed another suction point near the plumbing to take advantage of the settling that occurred. This suction point allowed us to reach the front corner of the house.

Additional Suction Point

This second suction point only moved about 9 CMF, so we didn’t need a 4-inch pipe here, but it was easier than going with a smaller pipe and bringing it back up. Once we installed the fan, it pulled about 110 CFM from the drain tile. We also had about 75 feet of 4-inch pipe. Using a 3-inch pipe would have added friction loss, and we would have needed a much bigger fan.

We knew we would have weak suction in the second addition, but the shop vac that we use to simulate fan suction during diagnostic testing isn’t as strong as an actual radon fan, so we weren’t sure how weak the suction would be. So we added a tee with a cap so that we could tie in another suction point if we determined it was necessary. After installing the fan, we had -2.6 Pa in one part of the addition. In the other part, we had -1.6 Pa. On the sump in the addition, we had -0.1 Pa.

Because it was summer, there was not much stack effect. We did a max depressurization test where we turned on all the bath fans, which helped simulate what the house might do in the winter. When we turned on all those fans with just two suction points, the pressure in the sump in the addition went positive, which demonstrated that we’d likely lose suction in that portion of the house during the winter.


We decided to add a suction point in that second addition and tie it into the tee we mentioned earlier. This third suction point nearly doubled our pressure field extension in the addition without a significant energy penalty.

Additional Suction Point

Third Suction Point



We pitched all the pipes to drain to the suction point. When we use tees like the one below, we face them so that the air can flow smoothly up and through. To prevent water from accumulating by the sharp edge in the pipe, we use a Sawzall to nip a bit of that bottom part out. You could also get a tee that sweeps smoothly in both directions, but they are significantly more expensive.

Pitched Pipes

Prevent water accumulation


The pipe went up through a closet on the first floor from the basement. We mounted the manometer and alarm on the pipe in the first floor closet because we thought the homeowner would spend more time on the main floor than in the basement.

Manometer and Alarm

The pipe ran up through a second closet on the second floor and then exhausted out through the roof.

Running pipe through two closets on a two-story house can be challenging. So to help us figure out where to drill, we used Magnespot, a tool that uses a transmitter and receiver to help you see where you’re drilling. (As an Amazon Associate, we earn from qualifying purchases)

Magnespot transmitter to help drill

We also used a stud finder to ensure that we wouldn’t hit floor joists. We had to adjust for some blocking. Then, we drilled a half-inch hole and used the Milwaukee cable camera to get a 360-degree look below the floor to ensure we wouldn’t cut through plumbing or electrical. (As an Amazon Associate, we earn from qualifying purchases)


Now that we have shown you the process of radon mitigation with aftermarket drain tile and additions, let’s share the results.

The system achieved full pressure field extension. EcoTrackers (Use our code AmericanRadon at checkout for a 5% discount! We earn from qualifying purchases) scattered throughout the basement showed radon levels ranging from 0 pCi/L to 1 pCi/L.

The fan consumed 48 watts, moving about 110 CFM. We estimated about 70 of that came from the house. The operating cost was about $330 a year.

If you’re interested in getting your radon levels as low as possible, contact us for a free estimate.