Skip to content
RADON411
$5

County radon report

Get it
Owning and renting5 min read

How do you install a radon system in new construction?

By Radon411 Editorial TeamUpdated How we research

Short answer

In new construction, radon-resistant features go in with the foundation: a gravel layer under the slab, plastic sheeting over it, sealed cracks and openings, a vent pipe from the gravel to the roof, and an attic junction box. The pipe works passively, and a fan is added if a test after move-in shows radon is still high.

Next step: check the rules where you rent or let. Radon rules for rentals by state

The gravel layer, a 4-inch layer of clean, coarse gravel or an alternative such as a perforated pipe or collection mat, lets soil gases move freely under the house. Heavy-duty plastic sheeting on top keeps soil gas out and keeps the concrete from clogging the gravel. Openings, cracks and crevices in the foundation are sealed with polyurethane caulk.

A 3-inch or 4-inch PVC vent pipe runs from the gravel layer up through the house and out the roof, labeled as a radon system, and an attic junction box is ready for a vent fan. A plumber or a certified radon professional can install the pipe.

These features usually cost less to include during construction than fixing the home later. Every new home should still be tested after occupancy; if radon is still high, a qualified mitigator adds a fan to activate the system.

What to do next: if you are building, ask your builder about radon-resistant features before the foundation work begins. If you are buying a new home, ask whether it has them, and test after moving in.

The five radon-resistant features

In new construction, the radon system goes in with the foundation. Builders can construct new homes that are resistant to radon entry, and no special skills or materials are required. Five basic features do the work.

The five basic radon-resistant features
FeatureWhat it isWhat it does
Gas-permeable layerA 4-inch layer of clean, coarse gravel below the slab; a perforated pipe or collection mat where gravel is impracticalLets soil gases, radon included, move freely under the house
Plastic sheetingHeavy-duty 6 mil polyethylene or a vapor retarder on top of the gravelHelps keep soil gas out, and keeps concrete from clogging the gravel
Sealing and caulkingPolyurethane caulk in openings, cracks and crevices in the floor and walls, including the slab perimeter crackKeeps radon and other soil gases from entering
Vent pipeA 3-inch or 4-inch solid PVC Schedule 40 pipe from the gravel layer through the house and roof, labeled as a radon systemVents radon and other soil gases safely outside above the house
Junction boxAn electrical outlet in the atticReady for a vent fan if testing shows one is needed

Passive first, active if needed

Built this way, the system starts out passive. Passive subslab suction works like the active kind but relies on natural pressure differences and air currents instead of a fan to draw radon up from below the home.

Cross-section of a house with a sub-slab depressurization system: soil gas drawn from beneath the slab into a suction point, up a vent pipe, through a fan outside the living space and out above the roofline.
Read this figure as text
Sub-slab depressurization system in a house cross-sectionGround levelLiving spaceBasement12345
  1. Soil gas drawn from beneath the slab
  2. Suction point through the slab
  3. Vent pipe
  4. Fan, outside the living space
  5. Discharge above the roofline
The same pipe, with a fan added, becomes an active sub-slab system.

If a test after move-in shows radon is still high, the passive system should be activated by having a qualified mitigator install a vent fan on the existing pipe. An alarm goes in with the fan to show when it is not operating properly. The cost is much less when the passive system was installed during construction.

Building it in, step by step

  1. Before the slab

    Lay the gas-permeable layer: 4 inches of clean, coarse gravel, or a perforated pipe or collection mat.

  2. Cover it

    Place heavy-duty plastic sheeting or a vapor retarder over the gravel before the concrete is poured.

  3. Stub up the pipe

    Set the vent pipe in the gravel layer when the slab is poured, then run it up through the house and out the roof. A plumber or a certified radon professional can do this.

  4. Seal

    Caulk openings, cracks and crevices in the foundation floor and walls, including the slab perimeter crack.

  5. Wire for later

    Put an electrical junction box in the attic for a future vent fan.

Why build it in now

Including these features during construction usually costs the builder less than fixing the home later. If a home is tested after the buyer moves in and an elevated level is found, the owner's cost of fixing it can be much more. Radon-resistant techniques may also help lower moisture and other soil gases.

Building in against fixing later
FactorBuilt in during constructionAdded after move-in
Gravel layer and sheetingGo in before the slabNot in place
CostUsually lessCan be much more
Upgrading to activeAdd a fan to the existing pipeA system must be added

Building codes in your state or local area may require these features. See radon-resistant new construction.

Test after you move in

Radon-resistant construction does not replace a test. Every new home should be tested after occupancy, even if it was built radon-resistant, in the lowest lived-in level. If the level is still high, activate the system with a fan and test again.

Timeline after a radon mitigation system is installed: the fan runs continuously, test no sooner than 24 hours and within 30 days, then retest at least every two years.
Read this figure as text

  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.

Testing after a system is installed or activated: the first check, then regular retests.

See testing a new home for radon.

Questions about radon systems in new construction

What are radon-resistant construction techniques?

A gas-permeable layer under the slab, plastic sheeting over it, sealing and caulking, a vent pipe to the roof, and an attic junction box for a future fan.

Does a new home need a radon test?

Yes. Every new home should be tested after occupancy, even if it was built radon-resistant.

Is a passive radon system enough?

Sometimes. If a test shows radon is still high, a qualified mitigator adds a vent fan to make it active.

Who installs the radon pipe in a new house?

A plumber or a certified radon professional can install the vent pipe.

Can I ask my builder to add radon features?

Yes. A new home buyer may ask the builder about these features, and if they are not provided, ask the builder to include them.

Are radon-resistant features required by code?

Building codes in your state or local area may require them. Check with your builder or local building department.

Owning and renting

Related guides

Living with a home over the years: retests, a system to look after, and new builds.

Everything in Owning and rentingOther guide topics
  • 20 min read

    Radon system

    Living with a radon mitigation system, from the manometer to maintenance and retesting.

    Read the guide
  • 19 min read

    Passive radon system

    How radon-resistant construction works, whether it is enough, and how to make it active.

    Read the guide
  • Overview page

    Testing a new home for radon

    Why a new home still needs a radon test, when to test after move-in, and what to do if the result is elevated.

    Open the page