Radon Mitigation

Background

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 in the US each year 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.

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, beginning January 1, 2019, this individual must be licensed by the Minnesota Department of Health Radon Licensing Program.

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 or successor ANSI-AARST Standard).

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

New Construction

All new multifamily type buildings without underground parking shall provide a Passive sub-slab depressurization system. For the purpose of system design, the subfloor preparation, vent pipe, electric outlet and other requirements under the Minnesota State Building Code for Single Family new construction and other applicable residential structures shall apply to new multifamily construction with the following amendments:
  • Vertical Vent Pipes with electric outlet, meeting the following requirements:

    • An electric outlet shall 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 shall be converted to an Active system by:

    • Adding a fan which 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 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.

  • Where to Test. In summary, ANSI/AARST MAMF 2017 requires:
    • "...a measurement in each ground contact apartment, dwelling and those rooms that are used as office space."
    • "On upper floors, conduct a measurement in at least one apartment on each floor, include measurements in at least 10 percent of the dwellings on each of the higher floors."

Substantial Rehab

All multifamily Substantial Rehab projects must provide, at a minimum, a Passive sub-slab depressurization system, which meets the requirements defined under the Minnesota State Building Code for Single Family new construction and other applicable residential structures with the following amendments:
  • Vertical Pipe installation must be provided per 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.
    • Or, a Performance approach, which involves a custom analysis and design by a Radon Contractor/ Mitigation Service Provider as described earlier in accordance to 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 or successor ANSI-AARST Standard.
  • All ground-connected dwelling units and at least 10 percent 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.

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, again at post construction
  • Testing protocols must be as per the ANSI/AARST MAMF 2017 or successor ANSI-AARST Standard
  • Exception: Testing may not be required based upon program funding, limited scope or other reason determined by Minnesota Housing.
Radon mitigation is required for:
  • Regardless of testing strategy, if testing results finds Radon levels to be 4 pC/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” below)
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).

Projects with Underground Garages (no other ground contact space)

Radon testing is not required for any buildings (new, substantial rehab, or moderate rehab) with underground garage designed and vented to meet applicable Minnesota codes and regulations. Underground garages vented as such do not require any other source of Radon control.

Resources