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How to Install Radon Mitigation

In this how-to video, This Old House host Kevin O'Connor discovers an effective method of clearing radon from a home.

What Is Radon?

An odorless gas, radon is the result of the nuclear decay of naturally occurring uranium in the earth. Radon is a radioactive gas and known to be a carcinogen. It’s not a problem everywhere, but the bedrock in some regions produces enough radon for it to concentrate on basements enough to raise the risk of lung cancer.

Steps for Installing Radon Mitigation

Radon test kits are readily available online and in-home centers. Beyond a certain level, the EPA recommends a fan-powered suction system to evacuate radon from the house.

Step 1: Make a hole

Using a rotary hammer, drill a hole in the basement slab large enough to receive a 3-inch plastic pipe. Kevin uses a vacuum to control the concrete dust.

Step 2: Dig out under the slab

A drill-powered auger is used to dig a small pit below the slab. If the layer below is granular, such as gravel, only a small pit is needed. If the soil is dense, a larger pit is needed to increase the area the fan will pull from. Dig this by first loosening the soil under the slab then vacuuming it out.

Step 3: Run pipe from cellar to attic

Find a path to run a 3-inch PVC pipe through the house and into the attic. Glue the joints together, support the pipe where needed with straps, and make sure the horizontal runs pitch back to drain condensation.

Step 4: Place and seal pipe

Run the bottom piece of pipe several inches into the sub-slab pit. Place the backer rod between the outside of the pipe and the slab, then seal the joint using hydraulic cement.

Step 5: Run the pipe to a fan

In the attic, the pipe runs to an in-line fan that runs 24/7. You’ll probably need to add an outlet to plug in the fan. Insulation around the pipe helps minimize condensation inside pipes run in unheated attics. The pipe exits the attic through the roof. That penetration is flashed to keep out water using a standard plumbing boot.

Step 6: Install a manometer

With the fan running, a simple gauge installed in the pipe in the basement lets the homeowner verify that the system is working.

Step 7: Test the system

Small holes drilled in a couple of locations in the basement are used to test the suction. Smoke from a smoke-pencil sucked into the holes verify the system’s effectiveness. The holes will be plugged with hydraulic cement after the test.

Consider Hiring a Pro

Although the work seems straightforward, it requires knowledge of several different trades from plumbing to electrical to roofing. In many states, radon mitigation requires a license. After all the work is done, the house will be re-tested for radon. If the levels are still high, additional pipes may be drilled into the slab and connected to the same fan.


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