Radon Mitigation

Revised: February 11, 2022

Background

Per the Minnesota Department of Health, Indoor Air Unit, radon is a colorless, odorless radioactive gas that seeps up from the earth. When inhaled, it gives off radioactive particles that can damage the cells that line the lung. Long term exposure to radon can lead to lung cancer. In fact, more than 21,000 lung cancer deaths are caused by radon, making it a serious health concern for Minnesotans.

In Minnesota, more than two in five homes have radon levels that pose a significant health risk, and nearly 80 percent of Minnesota counties are rated high radon zones. Some factors that further contribute to Minnesota's high radon levels include:

  • Minnesota's geology produces an ongoing supply of radon.

  • Minnesota's climate affects how our homes are built and operate.

Requirements

All multifamily projects receiving funding from Minnesota Housing must meet requirements as described herein.

Testing

All radon testing/measurement must be provided by an individual certified by the National Radon Proficiency Program (NRPP) or the National Radon Safety Board (NRSB). In addition, this individual must be licensed by the Minnesota Department of Health Radon Licensing Program and approved to conduct radon work in multifamily buildings.

Testing protocols must be as per the American National Standards Institute – American Association of Radon Scientist and Technologist (ANSI-AARST) Standard: “Protocol for Conducting Radon and Radon Decay Product Measurements in Multifamily Buildings” (ANSI/AARST MAMF 2017 with January 2021 Revisions or successor ANSI-AARST Standard).

Testing must be documented with radon report submitted to Minnesota Housing at the project phases noted below.  All radon reports must include the results of any testing performed, the details of any mitigation deemed necessary, and the timing to complete any such mitigation.

Post-mitigation Reporting

A certificate of completion must be submitted to Minnesota Housing and appended to the radon report once radon testing and/or mitigation are completed.

Resident Notification

Residents must be informed of forthcoming testing in the manner described in the ANSI-AARST MAMF.

Residents must be informed both prior to and after mitigation activities. In the case of new construction, incoming residents must be informed of radon mitigation activities.

Regardless of project tupe, an exterior radon mitigation system is not allowed.

Refinancing (Refi) With or Without Rehabilitation

Testing must be performed no earlier than one (1) year prior to submitting an application for funding to Minnesota Housing regardless of whether or not the refi includes rehabilitation. In addition, testing is required regardless of whether or not an underground garage is present.

If the refi does not include rehabilitation and testing results find radon levels to be 4 picocuries of radon per liters of air (pCi/L) or greater, an active radon mitigation system must be installed to fix the building prior to closing.  If test results are within 2-4 pCi/L, an active mitigation system is not required but is strongly encouraged.  When required, the following procedures must be used for the active radon mitigation system:

  • Consult with a radon contractor or mitigation service provider as described earlier to identify and design a radon control system; and/or
  • Consult with the Minnesota Department of Health, Indoor Environments & Radiation Section, indoor Air Unit (refer to the Radon Technical Assistance in the "Resources and Links" section below)

If the refi does include rehabilitation and testing results find levels to be 4pCi/L or greater, a mitigation system must be installed to fix the building prior to loan closing or it must be included in the rehabilitation scope of work per the Substantial Rehab or Moderate Rehab mitigation requirements below.  If test results are within 2-4 pCi/L, an active mitigation system is not required but is strongly encouraged.

New Construction without an Underground Parking Garage

All new multifamily type buildings without underground parking garage must provide a passive sub-slab depressurization system. For system design, the subfloor preparation, vent pipe, electric outlet and other requirements under the Minnesota State Building Code 1303.2400-1303.2403 for all new residential structures must apply to new multifamily construction with the following amendments:
  • Vertical vent pipes with electric outlet, meeting the following requirements:

    • An electric outlet must be provided at the top/attic location of each vertical vent pipe to allow conversion to an active system.

    • Provide at least one 4” diameter (in lieu of 3”) vertical vent pipe per 3,000 square feet of building foot print

    • Townhome Buildings

      • At townhome buildings without a continuous gas-permeable material below the concrete slab between dwelling units, at least one 4” diameter vertical vent pipe per dwelling unit must be provided. 

      • If the gas-permeable material below the concrete slab is connected and continuous at townhome buildings, one 4” diameter vertical vent pipe per 3,000 square feet of building footprint must be provided. Horizontal sleeves (4” in diameter at 10’-0” on center) through foundations and footings are allowed as part of a connected and continuous gas-permeable material and radon control system. 

  • All ground-connected dwelling units and at least 10% of randomly selected dwelling units on upper level floors (at least one per each floor) must be tested when the project is complete (prior to initial occupancy). If testing finds radon levels to be 4 pC/l or greater, the passive system must be converted to an active system by:

    • Adding a fan that remains in full operation continuously and is approved by manufacturer for radon use.

    • In apartment buildings with common area, the continuously operating fan must be tied to a common area's power source.

    • In rental townhome buildings (without common space), the continuously operating fan(s) must be tied to a common power source (meter) or tied to a unit meter with a sub-meter to allow power cost to be prorated among all units with the building.

  • Where to Test. Per ANSI/AARST MAMF 2017 with January 2021 Revisions requires:
    • Conduct a measurement in each ground contact dwelling unit and those rooms that are used as office space.
    • Conduct a measurement in at least 10% of randomly selected dwelling units on upper level floors with at least one measurement per each floor
  • If test results are within 2-4 pCi/L, an active mitigation system is not required but is strongly encouraged.

New Construction with an Underground Parking Garage

New multifamily buildings with an underground parking garage are not required to provide a passive sub-slab depressurization system; however, a post-construction test must be provided per ANSI/AARST MAMF 2017 with January 2021 Revisions:
  • Conduct a measurement in each ground contact dwelling unit and those rooms that are used as office space.
  • Conduct a measurement in at least 10% of randomly selected dwelling units on upper level floors with at least one measurement per each floor
If testing results finds radon leves to be 4 pCi/L or greater, an active radon mitigation system must be installed using one or both of the following procedures:
  • Consult with a radon contractor or mitigation service provider as described earlier to identify and design a radon control system; and/or
  • Consult with the Minnesota Department of Health, Indoor Environments & Radiation Section, Indoor Air Unit (refer to the Radon Technical Assistance in the "Resources and Links" section below)
If test results are within 2-4 pCi/L, an active mitigation system is not required but is strongly encouraged.
 
Exception: Unless required by federal funding or other funding source(s), new construction projects with an underground parking garage funded prior to April 2022, are not required to provide post-construction radon testing.

Substantial Rehabilitation (Rehab)

See Chapter 3 of the Multifamily Rental Housing Design/Construction Standards for definition of Substantial Rehab.

All multifamily Substantial Rehab projects must provide, at a minimum, a passive sub-slab depressurization system, which meets the requirements under the Minnesota State Building Code 1303.2400-1303.2403 for all new residential structures with the following amendments:
  • Vertical Pipe installation must be provided by a MDH licensed radon mitigation professional per either of the following Prescriptive or Performance approaches:
    • A Prescriptive approach must include:
      • At least one 4” diameter (in lieu of 3”) vertical vent pipe per 3,000 square feet of building foot print; or,
      • At least one 4” diameter vertical vent pipe per dwelling unit (at townhomes).
      • At each vertical pipe location, the pipe must extend 1” below the concrete slab into a suction pit (void area), that is a minimum 3’ in diameter and 1’ deep.
    • A performance approach, which involves a custom analysis and design by a radon contractor/ mitigation service provider certified by the NRPP or the NRSB. In addition, this individual must be licensed by the Minnesota Department of Health Radon Licensing Program.  The system shall meet the requirements of  ANSI/AARST “Radon Mitigation Standards for Multifamily Buildings” (ANSI/AARST RMS-MF 2018 or successor standard).
  • Testing protocols must be as per the ANSI/AARST MAMF 2017 with January, 2021 Revisions or successor ANSI-AARST Standard.
  • All ground-connected dwelling units and at least 10% of randomly selected dwelling units on upper level floors (at least one per each floor) must be tested when the project is complete (prior to initial occupancy). If testing finds radon levels to be 4 pC/l or greater, the passive system must be converted to an active system by:
    • Adding a fan, which remains in full operation continuously and is approved by the manufacturer for Radon use.
    • In apartment buildings with common area, the continuously operating fan must be tied to a common area power source.
    • In rental townhome (without common space) buildings, the continuously operating fan(s) must be tied to a common power source (meter) or tied to a unit meter with a sub-meter to allow power cost to be prorated among all units with the building.
  • If test results are within 2-4 pCi/L, an active mitigation system is not required but is strongly encouraged.

Moderate Rehabilitation (Rehab)

See Chapter 3 of the Multifamily Rental Housing Design/Construction Standards for definition of Moderate Rehab.

Radon testing is required for:

  • Projects with work scopes that do not influence radon concentrations in buildings:

    • During the preconstruction phase (prior to loan commitment/ loan closing)
  • Projects with work scopes that will, or are likely to, increase building depressurization and/or reduce amount of fresh air ventilation:
    • During the preconstruction phase (prior to loan commitments/ loan closing) and
    • At post construction
  • Testing protocols must be as per the ANSI/AARST MAMF 2017 with January 2021 Revisions or successor ANSI-AARST Standard
  • Exception: Testing may not be required based upon program funding, limited scope or other reason determined by Minnesota Housing's sole discretion.
Radon mitigation is required for:
  • Regardless of testing strategy, if testing results finds radon levels to be 4 pCi/L or greater, an active radon mitigation system must be installed to fix the building as part of the work scope during construction, post construction, or sooner, with following procedures:
    • Consult with a radon contractor or mitigation service provider as described earlier to identify and design a radon control system; and/ or
    • Consult with the Minnesota Department of Health, Indoor Environments & Radiation Section, Indoor Air Unit (see Radon Technical Assistance in the “Resources and Links” section below)

If test results are within 2-4 pCi/L, an active mitigation system is not required but is strongly encouraged.

All radon mitigation systems must be installed in accordance with ANSI/AARST “Radon Mitigation Standards for Multifamily Buildings” (ANSI/AARST RMS-MF 2018 or successor standard).

Resources