Radon-resistant new construction: the five features and how to activate them

There are five basic features. The techniques can vary with the foundation and the building site, but the elements are the same:

Two more pieces belong on the electrical side: a separate junction box in the living space to power the fan alarm, and an alarm installed with the fan to show when it is not working properly.

With no fan, the pipe relies on the house itself. A passive system is a vertical vent pipe rising from a sub-slab collection pipe or mat, through the conditioned space and out the roof, where the natural stack effect pulls soil gases up and out. An active system adds an in-line fan in the vertical pipe to pull the gases out.

The features are adapted to the foundation. The gas-permeable layer is used only under basement and slab-on-grade foundations, not crawl spaces. In a crawl space, the plastic sheeting, with its seams sealed, goes directly over the crawl space floor. A house with more than one foundation type should have each segment treated separately with the techniques that fit it.

1. 1

   Pick the route

   A vertical run through a warm part of the house, out through the roof. Routing the pipe up an outside wall reduces the natural stack effect and the system's effectiveness.

2. 2

   Size it

   Passive systems tend to work better with 4-inch pipe than 3-inch.

3. 3

   Lay the collection

   On a slab, a perforated pipe of at least 3 inches in a gravel trench or a collection mat, looped so soil gas enters from both sides and connected to a vertical T.

4. 4

   Cover and label before the pour

   Place the polyethylene around the T, cap the open top and label the pipe as part of the radon system before the concrete goes in; seal around the T after curing.

5. 5

   Run the pipe up

   Avoid 90-degree angles in the vertical run, using sweeps for turns, and label the pipe on each floor so it is not mistaken for the sewer system.

6. 6

   Through the attic and roof

   Insulate the pipe through an unconditioned attic to control condensation, flash it properly, and fit a screened cap.

7. 7

   Place the exhaust

   At least 1 foot above the roof, protected from snow drifts, and 10 feet from any openings so soil gas does not re-enter.

Several codes and standards describe radon-resistant construction, and building codes in your state or local area may require the features. The main ones:

When you talk to a builder, ask whether they use a recognized approach, such as the International Residential Code Appendix F, ASTM E 1465-08 or the ANSI/AARST standards. More on the codes is in the passive radon system guide.

The guidance centers on Zone 1, the counties the national zone map rates highest potential. EPA recommends that all homes built in Zone 1 have radon reduction systems, and the National Association of Home Builders also recommends the passive system there. The Indoor airPLUS label requires radon-resistant construction in Zone 1 and recommends it in Zones 2 and 3.

An EPA radon zone describes predicted potential across a whole county. It is not intended to determine whether any individual home should be tested, and homes with elevated levels occur in all three zones. EPA recommends testing every home regardless of zone, and testing is the only way to know the radon level in a specific building. Local levels may differ from the county map, and how much radon a home will collect cannot be known until it is built. Check your county's zone on the radon map.

The 2001 figures are old. Today the cost to a builder can vary widely and is typically less than the cost to mitigate the home after construction, and it is almost always less expensive to build the features in than to fix an existing home. Current mitigation figures are on radon mitigation cost.

Yes, with a test to confirm. The passive system reduces radon by about 50 percent on average and, in most cases, to levels below the action level, and virtually all homes with an active system are below 4 pCi/L. The techniques, installed properly and completely, can help reduce indoor radon, and installing them at construction makes it easier and cheaper to go further if the passive system does not get below 4 pCi/L.

There are side benefits too. The features can reduce moisture and other soil gases, and they can make a home more energy efficient.

The features do not replace a test. Every new home should be tested after occupancy, even if built radon-resistant, and if radon is still above 4 pCi/L the passive system should be activated by a qualified mitigator installing a vent fan. EPA recommends fixing a home when the radon level is 4 pCi/L or higher.

1. 1

   Test the house

   A short-term or long-term test on the lowest lived-in level; see new home radon testing.

2. 2

   If it tests at 4 pCi/L or more, activate

   Have a credentialed or licensed contractor install and switch on an in-line fan in the vent pipe, using the attic junction box.

3. 3

   Add the alarm

   An alarm installed with the fan shows when it is not working properly.

4. 4

   Retest

   Retest after activation, then every two years and after major renovations.

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1. Day of installation

   The system goes in

   Keep the fan running at all times: it must run continuously for the system to work correctly.

2. No sooner than 24 hours

   Earliest post-mitigation test

   Test no sooner than 24 hours after your system is in operation with the fan on, if it has one.

3. Within 30 days

   Post-mitigation test done

   A two- to seven-day measurement is recommended, and EPA recommends an independent follow-up radon measurement as well as any test the contractor runs.

4. At least every two years

   Retest

   Retest your home at least every two years to be sure radon levels remain low.

Test conditions: Windows and doors must be closed 12 hours before and during the test, except for normal entry and exit. Not drawn to scale.

After a remodel. After you remodel, retest in the lowest lived-in area to make sure the construction did not reduce the effectiveness of the radon reduction system.

Do not rely on it. Soil testing is not recommended for deciding whether to build radon-resistant: it cannot rule out a radon problem in the house you build, because site preparation can open new pathways and the house itself creates a vacuum that cannot be predicted. It also costs more than it seems, a single soil test ranging from $70 to $150 with at least 4 to 8 tests needed for one site, against the cost of simply installing the passive system.

Ask whether radon-resistant features were used and whether the home has been tested; check whether the home is in a high radon area; and if the features are not standard, ask the builder to include them, using the published model standards and architectural drawings to explain the techniques.

If the home is already built without the features and tests high, it can still be fixed with a standard system; see radon mitigation. For buyers generally, see buying a house with radon.