Radon Mitigation Design for New Schools

A radon mitigation design for a new school is an engineered soil gas control package drawn to ANSI/AARST CC-1000-2018, the consensus standard that sets prescriptive minimum requirements for the construction of any building intended for human occupancy other than one- and two-family dwellings, and that names educational occupancies in its scope. It is a design deliverable for the permit set, not an installation bid: sub-slab collection plenums, a continuous soil gas barrier, vent pipe routing and sizing, and the provisions that let a passive system convert to active without opening a finished slab.

Schools are the occupancy where that work pays back fastest, because control built into a slab costs a fraction of coring an occupied elementary school over a summer break. The EPA recommends testing all schools for radon and reports that thousands of classrooms nationwide have elevated levels. Radon is the leading cause of lung cancer among non-smokers, and CC-1000 places educational occupancies in the same scope as multifamily and commercial construction.

New construction and existing buildings answer to different standards, and naming the wrong one on the cover sheet costs a plan review cycle.

• A new school is designed to CC-1000-2018. The EPA lists it as a radon standard of practice under its full title, Soil Gas Control Systems in New Construction of Multifamily, School, Commercial and Mixed-Use Buildings, at Rev. 5/23.
• An existing school is mitigated to SGM-MFLB-2023. In 2023 AARST consolidated the mitigation standards for multifamily buildings and for schools and other large buildings, RMS-MF and RMS-LB, into a single publication, SGM-MFLB-2023. The measurement standards MAMF and MALB merged the same way, into MA-MFLB-2023.

Both can apply on one site. A district adding a wing to an occupied building designs the addition to CC-1000 and mitigates the existing structure to SGM-MFLB-2023. If the two are drawn as one scope against one standard, the reviewer sends it back.

The package is the document set the contractor builds from and the plans examiner stamps. For a school it covers the whole footprint, including the areas people assume are exempt: mechanical rooms, below-grade tunnels, and crawl spaces under stage or gym floors. A complete package specifies:

• The sub-slab collection layout, with the gas-permeable layer, every suction point, and the plenum boundaries created by interior footings and slab breaks.
• A continuous soil gas barrier, with the membrane type, the lap dimensions, and the sealing detail at every pipe penetration, footing, and construction joint.
• Vent pipe routing and sizing from each plenum through conditioned space to a discharge above the roofline, clear of operable windows and outdoor air intakes.
• Passive and active provisions on the same sheets: the fan location, the accessible service space, the electrical rough-in, and the labeling.
• Code references and a certified radon professional's review, so the credential the compliance chain expects is already inside the deliverable.

This is where a school diverges hardest from an apartment building. Section 4.3 of CC-1000 caps how much plenum area a single vent pipe may serve, and the caps are smaller than most people expect. In the basic configuration a 3 inch pipe serves 2,500 square feet, a 4 inch pipe 4,500 square feet, and a 6 inch pipe 10,000 square feet. Section 4.4 adds that no less than 90 percent of any 4,500 square foot slab or membrane expanse has to be vented by inlets joined to a vent system.

Run that against a 60,000 square foot single-story school and the arithmetic is immediate. It is not one system. It is a set of plenums bounded by interior footings, each sized to the table, some joined to a shared trunk and some standing alone. Getting the count wrong at design stage is what produces the classic retrofit: a passive stack that cannot hold a pressure field under a gym slab.

The standard also rewards verification. If plenum inspections are conducted per Sections 5.10.2 and 6.5, the same pipe sizes carry 3,500, 6,200, and 14,000 square feet. Add a virtually airtight barrier such as a spray-applied membrane and the allowances rise again, to 4,000, 7,100, and 16,000 square feet. Designing the inspections in, rather than hoping for them, can remove entire systems from a large school.

Every CC-1000 school design starts passive and is engineered to go active without rework. A passive stack uses the same physics that pulls radon in. Because indoor air pressure sits below soil pressure, the building acts like a vacuum drawing soil gas through floor-wall joints, expansion joints, and pipe penetrations. Warm air rising in a properly sized stack reverses enough of that draw to vent the plenum with no fan and no power.

The penalty clause in Section 4.3.4 is the reason the active provisions are not optional. If the barrier is not built continuous, or the gas-permeable layer and soil gas inlets do not meet Sections 5.5 and 5.7, the allowable plenum area drops to 1,250, 2,250, and 5,000 square feet by pipe size, and to zero square feet for any passive design. A field defect on a school slab can therefore invalidate a passive scheme outright. If the fan position, service access, and circuit were drawn from the start, that becomes a one-line field change instead of a redesign.

Occupancy testing settles the final configuration. EPA's action level is 4 pCi/L, and because there is no known safe level of exposure it recommends considering a fix below that number as well. Test the ground-contact rooms, and where results sit high, energize the fans at the positions the drawings already located.

The design is drawn from the actual building, so it starts with the plans. Send a vector PDF architectural set exported from CAD or Revit. The foundation geometry sets the plenum boundaries, the plenums size the ducts against Table 4.3, the stacks route to compliant discharge points, and the barrier and sealing details are specified at every penetration. A certified radon professional reviews and signs the result, and the package drops into the permit set as a standalone, code-referenced document.

If a new school, addition, or district facility is in design, start with the school building-type page for what the package covers and how the standard applies, or read the CC-1000-2018 standard breakdown first. Send the plans and a fixed quote comes back before any work begins, with no retainer and no bundled installation contract.