Radon

Back when we started construction of the foundation, someone asked me if we were going to include a radon mitigation system.  My response was something along the line of, “No.  We don’t need one.  It’s a Passive House and will be so well sealed no radon will be able to creep into the structure through the basement foundation.”  So much for uninformed confidence.

Flash forward to last month, when I came across a blog post by Paul Honig, who lives in a similar Passive House in Connecticut.  Surprisingly (at least to me) he wrote about his own discovery that his house had tested high in radon, and required the installation of a mitigation system.

In case you are unfamiliar with them, these mitigation systems are incredibly simple. Generally, a four to six inch hole is drilled through the basement slab.  Some stone and/or dirt is removed.  A PVC pipe is inserted.  The pipe is either run up and out through the rim joist (below the first floor) and then up to the roof, or all the way up through the attic to the roof.  A special fan is installed on the pipe, either outside the house or inside the attic.  The fan then runs 24/7, sucking air from under the slab, and thereby depressuring the sub-slab area and moving the radon outside. From what I’ve read, these systems generally cost around $1,000, give or take.

A homeowner can test for radon several different ways.  He or she can purchase a short term test on the web or at stores like Home Depot or Lowes.  They generally come with two vials.  The homeowner is then instructed on where to place them and how long to leave the caps off.  When the necessary amount of time has passed, the caps are replaced and they’re sent to the testing facility.  A week or so later, the results are viewable online.

Paul used a continuous electronic monitor called the Safety Siren Pro Series3 Radon Gas Detector, which sells for $130 through Amazon.com.  It’s very simple to use.  Just plug it in, wait 48 hours, and it starts providing a short and long term radon level reading, updated each hour.  The long term reading is an average of the hourly short term readings.

My curiosity was piqued enough to make the purchase.  Living is such a tight house, I had no desire to take a chance with radon just to save $130.  It proved to be a wise investment, as it reported a radon level of 6 pCi/L.  This is 150% above the remediation limit of 4 pCi/L.

I decided to check the accuracy of the Safety Siren by using a short term test that I purchased from Home Depot (that test cost me $15 plus a $30 lab fee).  The lab results showed one vial reporting a level of 4.7 pCi/L and the other reporting a level of 7.2 pCi/L.  The lab interpreted this to be an average reading of 6 pCi/L, the same as the Safety Siren.

I had almost zero enthusiasm for installing a traditional radon mitigation system.  Given the amount of insulation in the attic and the fact that the house has two stories, it would have been both difficult and messy to run a 4″ PVC pipe up through the roof.  Additionally, the first floor pent roof and the porch roof almost complete surround the house.  Therefore, there is very limited space to run an exterior pipe up the wall, and that space is near the front of the house, which would be less than appealing.  And finally, I have no desire to drill a 4″ hole through the basement slab and vapor seal.  Fortunately, after thinking about the issue for a while I came up with a possible alternative.

Instead of using wood to form the footers for our house, we used a product manufactured by Certainteed, called Form-a-Drain. Form-a-Drain footer forms are hollow, plastic, and have hundreds (or thousands) of small slots on both sides to allow water to drain away from the foundation.  Before the concrete is poured, a short section of PVC pipe is installed to connect the inner and outer forms.  Then another 4″ pipe is run to daylight to complete the drainage path.  Although I didn’t know it at the time, Certainteed bills the system as a “three-in-one concrete footing form system, foundation drainage system and sub-slab perimeter radon reduction system.”   Here are a couple of photos of the installation:

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The drain pipe on our house exits the ground on a slope about 30 feet from the southwest corner of the building. The idea I came up with was to install a Fernco rubber 4″ elbow on the end of the pipe, run a two-foot section of PVC up from that, install a radon fan on the top of that pipe, and cap the horizontal outlet.  My initial thinking was that no measurable water actually exited the drain, so I suspected that a cap wouldn’t cause a problem.  I was wrong.

During rain and melting snow, a fair amount of water did build up at the end of the drain pipe; somewhere between a half-gallon and a gallon per day.  In one sense, that complicated the installation of my radon mitigation system.  But on the other hand, I took it as a positive sign that the system was working as designed.  So I had to come up with a way to allow water to drain from the pipe while maintaining the system pressure being developed by the fan.

After doing some research, I concluded that there were two possible solutions to this problem.  The simplest would be to drill a few weep holes in the end cap; enough to let the water trickle out, but not so much that it would cause a critical drop in air pressure.  The other solution, which I chose, was to install a waterless “J-Trap” on the tee instead of a cap.  The product I found was the Hepvo Waterless Value, which sells for about $23.  It’s an incredibly simple device that works like a J-Trap in that it allows water to drain, while preventing sewer gas from entering the house.  But it does this without actually holding any water in a trap.  That’s important at our house because any sitting water would freeze in the winter.

For the fan, I chose to use the Energy Star-rated RadonAway RP-140, which can be found for less than $130 on the Web.  At 15-21 watts, it has, by far, the lowest draw of any fan I found.  It also has lowest airflow, maxing out at 135 CFM.  But everything I read indicated that it was more than sufficient to handle the problem.  Installation was incredibly simple; a Fernco union attached it to the lower pipe, another Fernco on top connected it to two PVC elbows (to keep rain water from entering the system.  For testing purposes, I ran an extension cord to one of our outdoor outlets, figuring that if the system works, I’ll run a buried line to it this summer.

And work it did.  It took a couple of days, but the radon level is now at 1.0 pCi/L, well below the 4 pCi/L limit.  The only things left to do are install the underground electric supply and disguise the fan and pipe, which should be much simpler than the alternative. Here are a couple of photos taken before I replaced the end cap with the Hepvo waterless J-Trap:

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