Passive radon system

A passive pipe works because warm air rises. Building Radon Out explains that warm air rises and will leak from openings in the upper portion of the house when temperatures are higher indoors than outdoors; this condition, known as stack effect, causes unconditioned replacement air to enter the lower portion of the house. The same force works inside the pipe: if the pipe is routed through warm space, such as an interior wall or the furnace flue chase, following local fire codes, the stack effect can create a natural draft in the pipe. Because this method requires no mechanical devices, it is called a passive soil depressurization system.

Building Radon Out also says sealing and caulking the rest of the building envelope reduces stack effect in the home, which lowers the suction the house puts on the soil. Every elbow costs draft: it says the vent pipe should be installed in a vertical run, with the least number of elbows which could restrict air flow, and that the additional elbows and horizontal pipe length will restrict air flow through the pipe if the system is activated.

EPA's radon-resistant construction page says the techniques may vary for different house foundations and building site requirements, but names the five basic features that builders should include to prevent radon from entering a home. All of the techniques and materials are commonly used in home construction, and no special skills or materials are required when adding radon-resistant features as a new home is being built.

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1. 1Cracks in solid floors
2. 2Construction joints
3. 3Cracks in walls
4. 4Gaps in suspended floors
5. 5Gaps around service pipes
6. 6Cavities inside walls
7. 7The water supply

Building Radon Out adds that in many parts of the country the gravel, plastic sheeting, and sealing and caulking are already employed for moisture reduction, and in these cases simply adding the vent pipe and junction box is extremely cost-effective for reducing radon. On pipe size it says that although some builders have used 3-inch pipe, field results have indicated that passive systems tend to function better with 4-inch pipe, which will also allow for a quieter system if the system is activated.

A passive system goes in while the foundation is built. EPA's Indoor airPLUS bulletin sets out best practices for a slab-on-grade home in five steps; the detail in brackets is from Building Radon Out.

1. 1

   Pick the pipe location

   A ventilation pipe of at least 3 inches in diameter, in a vertical run through a warm part of the house and exhausted through the roof, at least 1 foot above the roof and 10 feet away from any openings in the building. (Building Radon Out: a minimum of 12 inches above the surface of the roof.)

2. 2

   Lay the collection pipe

   A minimum 3-inch-diameter perforated pipe in a gravel trench, or a collection mat on top of the gravel, around the foundation perimeter, in a loop connected to either side of a vertical "T".

3. 3

   Cover, cap and label

   Place the polyethylene vapor barrier around the "T", cover its open top and label the pipe as part of the radon system before the concrete is placed. After curing, seal the perimeter of the "T" to the concrete. (Building Radon Out: label the stub so it is not mistaken for a sewer line.)

4. 4

   Run the vertical pipe

   Connect it to the "T", avoid 90-degree angles and use sweeps where turns are needed, and label the pipe on each floor so it is clear it is not part of the sewer system. Insulate it where it passes through an unconditioned attic.

5. 5

   Out through the roof

   Flash the pipe properly and fit a screened cap so debris and nesting animals stay out. (Building Radon Out: rain caps can reduce radon flow, and in most areas they are not needed.)

6. 6

   Wire for a future fan

   Building Radon Out: an unswitched electrical junction box in the attic or garage within 6 feet of the vent pipe. EPA's buyer's guide adds a separate junction box in the living space to power the vent fan alarm.

Plan the fan's place now. Building Radon Out lists the criteria for a future fan: it cannot be inside the living space of the house or in the crawlspace beneath the home; fans are most often located in attics or garages (unless there is living space above the garage); and fans require a 30-inch vertical run of pipe for installation. For the owner's side of the same project, see how to install a radon mitigation system in new construction and radon-resistant new construction.

A crawl space has no slab, so the plastic does the gravel's job. EPA's Home Buyer's and Seller's Guide says the gas-permeable layer is used only in homes with basement and slab-on-grade foundations; it is not used in homes with crawlspace foundations. Building Radon Out says crawlspaces are best treated by covering the entire crawlspace floor with plastic sheeting, laying a perforated collection pipe beneath the plastic sheeting, and connecting the pipe to the radon vent.

Whether a passive system is required depends on where you build. EPA's Citizen's Guide says building codes in your state or local area may require these radon-resistant construction features, and Building Radon Out tells builders: if your building code includes provisions for the radon features, follow your code requirements; if you don't already know what is required in your area, check with your local code official.

EPA's Home Buyer's and Seller's Guide gives a buyer the question to ask: if you're having a house built, ask your builder if they're using a recognized approach (International Residential Code, Appendix F, ASTM E 1465-08, and ANSI/AARST RRNC 2.0 as examples). EPA's Citizen's Guide recommends building new homes with radon-resistant features in high radon potential (Zone 1) areas, and Building Radon Out notes NAHB also recommends using the passive system in Zone 1. You can look up a county's predicted zone in the radon reports; a zone is a prediction for an area, not a reading of any house, and EPA's zone map says homes with elevated levels of radon have been found in all three zones.

So a passive system helps, and a fan helps more. EPA's Consumer's Guide says passive subslab suction is generally not as effective in reducing high radon levels as active subslab suction. Building Radon Out says that in most cases the passive system alone is enough to keep radon levels below 4 pCi/L, but that occasionally the homeowner will want or need to activate the system by adding a fan. EPA's Home Buyer's and Seller's Guide adds that radon-resistant techniques may also help to lower moisture levels and those of other soil gases.

Yes. A passive system narrows the ways radon can get in; it does not tell you the level in the finished house. EPA's Citizen's Guide says that even if built radon-resistant, every new home should be tested for radon after occupancy, and the Home Buyer's and Seller's Guide says as soon as possible after occupancy. The Indoor airPLUS bulletin explains why: the amount of radon that will accumulate in a home can't be determined until the home is built.

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Test	How long it runs	What it is for
Short-term test	Stays in the home from 2 to 90 days, depending on the device, and for a minimum of 48 hours.	A faster screening result. Because radon levels vary from day to day and season to season, it is less likely than a long-term test to tell you the year-round average.
Long-term test	Stays in the home for more than 90 days.	It is more likely than a short-term test to tell you the home's year-round average radon level.
Continuous monitor	Logs readings for the whole test, run as a short-term or a long-term test under the same durations in EPA guidance.	Logs a graph over time, so you can see trends and spot anomalies rather than a single number.

The test follows the same rules as any home: the lowest level that could be used regularly and a minimum of 48 hours. EPA recommends fixing a home when the radon level is 4 pCi/L or higher. EPA recommends considering a fix when the level is between 2 and 4 pCi/L. See how to test for radon, radon test kits and radon testing for new homes.

High radon with a passive system is what the junction box is for. EPA's Home Buyer's and Seller's Guide says that if you have a test result of 4 pCi/L or more, a vent fan can easily be added to the passive system to make it an active system and further reduce radon levels. EPA's Citizen's Guide says that if radon levels are still in excess of 4 pCi/L, the passive system should be activated by having a qualified mitigator install a vent fan, and the Indoor airPLUS bulletin says a credentialed and/or licensed contractor, depending on state requirements.

1. 1

   Test after move-in

   Run a valid test on the lowest level that could be used regularly.

2. 2

   Read the result

   EPA's page for buyers of newly built homes: if your home tests at 4.0 pCi/L or more, activate the system by installing an in-line fan.

3. 3

   Call a qualified mitigator

   Consult one or both of the national radon proficiency programs or your state radon contact for a list of qualified radon service professionals. See mitigation professionals.

4. 4

   Add the fan and the alarm

   The fan goes in the attic or garage on the junction box; EPA says an alarm is installed along with the vent fan to indicate when the vent fan is not operating properly.

5. 5

   Retest

   The Indoor airPLUS bulletin: EPA recommends re-testing your home after activation, and then every two years following or any time that major renovations or alterations are made to the home.

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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.

Average cost to activate a passive radon system

Radon411 does not quote a figure for activation. EPA's Citizen's Guide says to consult a qualified mitigator to estimate the cost of upgrading to an active system by adding a vent fan, and that the cost of fixing is much less if a passive system was installed during construction. Once the fan is in, the system is owned like any active system: see radon fans and living with a radon system.

The direction is the same everywhere: it is cheaper to build the features in than to fix a house later. EPA's radon-resistant construction page says the cost to the builder of including these features is typically less than the cost to mitigate the home after construction, and that if a home is tested after the buyer moves in and an elevated level of radon is discovered, the owner's cost of fixing the problem can be much more. CDC says it is almost always cheaper and easier to build these features into new homes than to add them later. Building Radon Out is the one source that puts numbers on it.

The $350 - $500 and $800 and $2500 figures are EPA's 2001 numbers; prices have changed since, and they are shown as EPA printed them. EPA notes that radon-resistant construction is part of or included in three labeling programs: EPA's Indoor AirPlus, the U.S. Green Building Council's LEED for Homes, and the National Association of Home Builders. Its radon-resistant construction page adds that radon-resistant features can be an important selling point for health-conscious home-buyers.

Look for the labels and the wiring, then ask. EPA's construction page says the vent pipe should be labeled "Radon System," and Building Radon Out recommends that the radon vent system be labeled in a conspicuous location on each floor level, so occupants and future occupants will know that it is part of a radon vent system.